For decades, ecologists have understood food webs through the lens of elemental ratios. Ecological stoichiometry, built on the famous Redfield ratio, treats carbon, nitrogen, and phosphorus as the fundamental currencies of life, tracking how these elements flow from algae to zooplankton to fish. Roy and Mraz acknowledge that this framework works reasonably well up to the level of primary producers. Plants, fungi, and protists genuinely do grow on free forms of elements, and the more nitrogen or phosphorus is fertilized into their environment, the more they grow. But the moment you move above the producers, the logic breaks down, and this is where the authors believe ecology has gone astray.

Animals, unlike plants, do not grow on free elemental nitrogen or phosphorus. They require biomolecules: proteins, lipids, carbohydrates, phospholipids, and specific amino acids. The evidence for this disconnect is striking. In fish, a meta-analysis of diet manipulation studies and field surveys found that the mean effect of dietary nitrogen-to-phosphorus ratios on excretion ratios was not significantly different from zero. This led researchers to hypothesize that future work must consider not just the ratios of nutrients in the diet but the molecular forms in which they are delivered. Roy and Mraz take this hypothesis to its logical conclusion: total nitrogen in seston or algae may be essentially meaningless for a zooplankter or a fish. What matters is the nitrogen bound in essential amino acids such as lysine and methionine, the carbon carried in digestible non-protein fractions like starch, and the phosphorus packaged in phospholipids rather than in apatite or phytate forms.

The authors illustrate this with concrete examples from fish nutrition. Supply the same amount of nitrogen to fish mainly through non-essential amino acids, and growth is modest; supply it through essential amino acids, and growth improves markedly. Deliver carbon through a high-protein diet versus non-protein energy fractions on an isoenergetic basis, and the non-protein route yields better growth. Phosphorus storage in fish remains low whenever key biomolecular packages are in short supply, regardless of how much total phosphorus the diet contains. These interactions, well documented in animal nutrition literature, are systematically overlooked in food web ecology, where carbon, nitrogen, and phosphorus are mathematically treated as if every atom were equivalent.

Why does this matter so much for animals? The answer lies in evolutionary physiology. Consumers above the primary producers have lost roughly half of their amino acid synthesis capabilities, including the ability to make essential amino acids. Unlike plants, animals cannot use photonic energy to synthesize biomass from absorbed elements; they must first catabolize energy-rich molecules to fuel the synthesis and storage of new matter. Their bodies are governed by homeostatic control, meaning they cannot simply mirror the elemental composition of their food. The fates of carbon, nitrogen, and phosphorus inside an animal, whether retained in biomass or excreted back into the environment, are dictated by a handful of key biomolecules whose required proportions shift relative to the energy available from non-key molecules.

This is where the rings of power concept acquires its practical teeth. When surplus energy comes from dietary non-key biomolecules such as starch, glycogen, saturated fats, or non-essential amino acids, the animal’s requirement for expensive key biomolecules drops, and more dietary nitrogen and phosphorus remain locked in body tissue. When energy from non-key biomolecules is inadequate, the animal is forced to burn its own key biomolecules for fuel, destroying them and releasing their nitrogen and phosphorus back into the water. In the authors’ framing, sufficient rings of power abolish the nutrient-energy transfer barriers between food and body and suppress nutrient leakage from consumers. When the rings are missing, ecosystems degrade into a soup of free nutrients: primary productivity overshoots, secondary and tertiary productivity stall, and the chain of trophic transfer efficiency breaks down entirely.

The concept has immediate relevance for one of the most stubborn water quality problems on the planet. Nutrients from human settlements, agricultural runoff, and farming accumulate in standing water bodies like the drain of a shower sink, driving harmful algal blooms and hypoxic dead zones. Roy and Mraz point out that specific rings of power, such as the amino acid lysine, saturated fatty acids, and the carbohydrate starch, go missing from pond plankton over the vegetative season or are absent throughout it. Their absence impedes the assimilation of nutrients into the bodies of aquatic consumers, leaving nitrogen and phosphorus freely available in the water column. Fish excretion alone can support a significant proportion of lake primary productivity, so the nutritional state of fish stocks directly modulates how much phosphorus recycles versus how much stays locked in biomass.

The proposed solution is audacious: design stoichiometrically corrective seasonal feeds spiked with the rings of power and deploy them in hypertrophic inland water bodies to convert pollution into harvestable biomass. In spring and autumn, digestible non-protein energy feeds would tip the balance; in summer, feeds balanced in essential amino acids and non-protein energy would sustain it. Well-fed fish with high metabolic satiety and gut fullness would graze less actively on zooplankton, allowing the planktonic food web to keep carbon, nitrogen, and phosphorus sequestered. Fish would additionally absorb orthophosphate directly from the water through their integuments, adding a second pathway for nutrient removal. Periodic stocking and harvesting of fish stocks would then physically crop the anthropogenic nutrients out of the ecosystem, transforming eutrophic ponds from points of pollution into regenerative solutions.

This approach deliberately exploits what the authors call a natural flaw. Natural food webs help digest nutrients, but metabolic assimilation is poorly constrained by stoichiometric errors and consumer homeostasis when diets are imbalanced. In nature, this is a deliberate error that keeps primary productivity running on the free nutrients leaked by consumers. Animal nutritionists have spent decades correcting precisely these flaws in commercial production systems, achieving far higher nutrient use efficiencies in poultry, pigs, and fish than were possible in the past. Roy and Mraz argue that this expertise, honed by commercial interest and physiological understanding, is exactly what ecology has been missing, and they call for the establishment of nutritional ecology as a formal field within educational and research organizations, with animal nutritionists trained and tasked to work on ecological applications.

The rings of power concept is, at this stage, a conceptual framework rather than a proven remedy, and the authors are candid about its speculative nature. Yet it arrives at a moment when conventional remediation, chemical treatments, and algae- or microbe-based biotechnologies struggle against the sheer scale of global eutrophication. If even a fraction of the framework holds under field testing, the implications ripple outward: pond aquaculture could become a nutrient-capture industry, fishponds across temperate Europe could double as water purification infrastructure, and the stubborn boundary between the science of what animals eat and the science of how ecosystems work might finally be bridged. Sometimes, the authors suggest, the most powerful tool for saving an ecosystem is not a new chemical or a new organism, but a better understanding of the molecular packages in which nature’s elements already travel.

Subject of Research: Biomolecular control of nutrient cycling in aquatic food webs and regenerative aquaculture

Article Title: The Rings of Power: managing nutrient cycles in aquatic food webs above and beyond primary producers

Article References: Roy, K., & Mraz, J. (2026). The Rings of Power: managing nutrient cycles in aquatic food webs above and beyond primary producers. Web Ecology, 26(1), 27-33. https://doi.org/10.5194/we-26-27-2026

Image Credits: AI Generated

DOI: 10.5194/we-26-27-2026

Keywords: nutrient cycles, aquatic food webs, ecological stoichiometry, eutrophication, fish nutrition, essential amino acids, phosphorus, nitrogen, zooplankton, aquaculture, biomolecules, water quality

Researchers at Gorgan University of Agricultural Sciences and Natural Resources in Iran, led by Delara Sepehrfar, fed goldfish (Carassius auratus) diets supplemented with pomegranate peel powder, or PPP, at inclusion levels of 1, 2, and 4 percent for 70 days. A control group received the basal commercial diet without any supplementation. The team distributed 240 goldfish, each weighing roughly 17 grams at the start, across twelve tanks with three replicate tanks per treatment. Water quality was tightly controlled throughout the trial, with temperature held at 25 degrees Celsius, dissolved oxygen above 6 milligrams per litre, and pH between 7.5 and 8.0. The work was approved by the university’s ethics committee and conducted in accordance with the ARRIVE guidelines for animal research.

Before the feeding trial began, the researchers chemically characterised the pomegranate peel powder using high-performance liquid chromatography. The analysis revealed a remarkably rich bioactive profile: a total phenolic content of 187 milligrams of gallic acid equivalents per gram, along with measurable quantities of punicalagin alpha at 24.8 milligrams per 100 grams and ellagic acid at 6.7 milligrams per 100 grams. These compounds are the chemical workhorses behind the peel’s reputation as a potent antioxidant, capable of scavenging free radicals and modulating endogenous defence pathways in living tissue.

The results, published on 9 October 2026, point to a striking dose-dependent pattern, with the strongest effects concentrated at the 4 percent inclusion level. Fish fed the highest dose of PPP showed a significant increase in total white blood cell counts, rising from 10.53 to 14.16 thousand cells per microlitre compared with controls. Serum lysozyme activity, a key marker of innate antibacterial defence, climbed from 32.85 to 51.62 units per millilitre, while total immunoglobulin concentration increased from 22.02 to 35.09 milligrams per decilitre. Notably, the differential leukocyte counts remained unchanged, suggesting that PPP stimulates overall leukocyte production rather than selectively expanding particular immune cell populations.

The antioxidant findings were equally compelling. Malondialdehyde, or MDA, a well-established marker of lipid peroxidation and oxidative damage, dropped by roughly half in the 4 percent PPP group, falling from 8.42 to 4.18 nanomoles per millilitre. At the same time, the activities of the enzymatic antioxidants superoxide dismutase and catalase rose significantly, and levels of reduced glutathione, the cell’s principal non-enzymatic antioxidant, more than doubled. Together, these shifts indicate that dietary PPP bolsters both arms of the antioxidant defence system, protecting cellular membranes, proteins, and nucleic acids from reactive oxygen species generated during normal metabolism and stress.

Serum biochemistry told a complementary story. Total protein and albumin concentrations increased markedly in the highest-dose group, while the activities of the liver enzymes aspartate aminotransferase and alkaline phosphatase declined, patterns consistent with improved hepatic function and protein synthesis. Cholesterol, triglycerides, and glucose all showed downward trends, although these did not reach statistical significance. Interestingly, alanine aminotransferase fell significantly at the 2 percent dose but returned toward control levels at 4 percent, a non-linear response the authors suggest could reflect complex dose-dependent effects of polyphenols on hepatic metabolism.

Perhaps the most eye-catching results concerned reproduction. After the feeding period, broodstock were injected with human chorionic gonadotropin to synchronise gamete maturation. Males fed 4 percent PPP produced sperm at significantly higher concentrations, with greater spermatohematocrit, longer motility duration, and a higher percentage of motile cells than controls. Females on the same diet produced larger eggs with more yolk space, achieved a fertilisation rate of 93.16 percent versus 88.26 percent in controls, and showed a gonadosomatic index of 5.33 percent compared with 3.36 percent. Relative fecundity jumped from roughly 1,237 to 2,066 oocytes per gram of body weight, and gonad weight more than doubled. The authors propose that the antioxidant protection afforded by PPP may safeguard gametes from oxidative damage, while certain phenolics such as ellagic and syringic acids may interact with endocrine pathways involved in vitellogenin synthesis and oocyte maturation.

Not every parameter responded. Mucosal immune markers measured in skin mucus, including lysozyme, alkaline phosphatase, and total immunoglobulin, showed positive numerical trends but no statistically significant differences among treatments. The authors suggest that the 70-day feeding period may have been too short, that inter-individual variability in mucosal responses was high, or that polyphenol metabolites simply do not reach mucosal surfaces in sufficient concentrations. Red blood cell counts, haematocrit, and haemoglobin were also unaffected, which the researchers interpret as evidence that PPP does not disrupt erythropoiesis at the tested doses.

The team is careful to frame these findings as preliminary and hypothesis-generating rather than definitive. The experimental diets were not formulated to be isonitrogenous or isoenergetic, meaning that adding PPP altered the overall protein, fat, and fibre content of the feed, so some metabolic changes could reflect altered nutrition rather than PPP bioactivity alone. The commercial basal diet may also have contained undisclosed additives that could interact with the supplement. All broodstock received HCG injections, so the reproductive gains might partly reflect enhanced responsiveness to the hormone rather than direct effects on reproductive physiology. Only three replicate tanks per treatment limited statistical power, no disease challenge test was performed, and no positive control such as vitamin E or beta-glucan was included for comparison.

Despite these caveats, the consistency of the responses across immune, antioxidant, metabolic, and reproductive endpoints lends weight to the idea that pomegranate peel could serve as a sustainable, multi-functional feed ingredient. Because the peel is an abundant, low-cost by-product that would otherwise be discarded, its use aligns with circular economy principles and could reduce reliance on synthetic additives at a time when antimicrobial resistance and environmental contamination have made the aquaculture industry eager for phytogenic alternatives. The authors call for confirmatory trials using semi-purified, nutritionally standardised diets, wider dose ranges, molecular measurements of cytokines and reproductive hormones, and pathogen challenge studies. If those trials bear out the preliminary signals, the humble pomegranate peel, currently destined for the landfill, may find a second life boosting the health and fertility of farmed fish around the world.

Subject of Research: Effects of dietary pomegranate peel powder supplementation on immunity, antioxidant status, and reproduction in goldfish

Article Title: Preliminary evaluation of dietary pomegranate (Punica granatum) peel powder effects on systemic immunity, antioxidant status, and reproductive performance in goldfish (Carassius auratus)

Article References: Sepehrfar, D., Sudagar, M., Siahkalroodi, S. Y., & Jafarnodeh, A. (2026). Preliminary evaluation of dietary pomegranate (Punica granatum) peel powder effects on systemic immunity, antioxidant status, and reproductive performance in goldfish (Carassius auratus). Discover Animals, 3(1), Article 102. https://doi.org/10.1007/s44338-026-00262-3

Image Credits: AI Generated

DOI: 10.1007/s44338-026-00262-3

Keywords: pomegranate peel, goldfish, aquaculture, immunity, antioxidant, oxidative stress, reproductive performance, phytogenic feed additive, polyphenols, Carassius auratus, functional feed, fish nutrition

Grass carp were an obvious choice for the investigation. As the most heavily farmed freshwater fish globally by production volume, the species carries enormous economic weight, and its herbivorous feeding habit made the team suspect it would be well suited to exploiting macroalgae as a feed ingredient. The researchers, led by Xingxing An and Qingyun Yan of Sun Yat-sen University’s Southern Marine Science and Engineering Guangdong Laboratory in Zhuhai, together with collaborators from industry and Hunan Agricultural University, designed a controlled feeding trial to test whether three chemically distinct seaweeds would produce different microbial and metabolic outcomes.

The experimental design was straightforward but rigorous. Young grass carp weighing roughly 91 grams were randomly assigned to one of four iso-nitrogenous and iso-lipidic diets: a control feed, or feeds supplemented with 5 percent powder of Sargassum hemiphyllum, Asparagopsis taxiformis, or Gracilaria lemaneiformis. The fish were reared for 52 days in a recirculating aquaculture system at 25 to 28 degrees Celsius, fed to apparent satiation twice daily, with no mortality recorded across the entire experiment. At the end of the trial, the team measured growth indices, collected serum and liver samples for immune and antioxidant assays, and aseptically sampled intestinal contents and feces for microbiome and metabolome analysis.

The physiological results immediately singled out one seaweed. Fish receiving the Sargassum diet showed significantly greater body weight, viscerosomatic index, and hepatosomatic index than controls, along with a marked boost in hepatic superoxide dismutase activity, a key antioxidant enzyme. The Asparagopsis group gained significantly in body length and viscerosomatic index, while the Gracilaria group produced more modest changes. Taken together, Sargassum hemiphyllum delivered the most comprehensive benefits for growth and antioxidant defense, hinting that its characteristic sulfated polysaccharides—compounds previously associated with immunomodulatory and anti-inflammatory activity—might be driving a distinctive microbial response.

Sequencing of the 16S rRNA gene from intestinal samples revealed a dramatic restructuring of the gut community. In control fish, the phylum Spirochaetota dominated at nearly 38 percent of the community, with the genus Brevinema as the standout member. In all three macroalgae groups, Spirochaetota collapsed to less than 0.03 percent, while Pseudomonadota surged—reaching over 61 percent in the Asparagopsis group. To pinpoint which genera truly distinguished the dietary groups, the researchers applied a Random Forest machine-learning classifier combined with differential abundance testing. One genus rose above all others: Shewanella, whose relative abundance increased significantly in the Sargassum group compared with controls. Other notable players included Vibrio, Bacteroides, and Butyricicoccus, the latter significantly enriched in the Gracilaria group.

To understand what these shifts meant functionally, the team turned to shotgun metagenomics, generating more than 392 gigabases of sequence data from fecal samples. From this they reconstructed 150 high-quality metagenome-assembled genomes, or MAGs—essentially draft genomes of the community’s constituent organisms. Functional annotation showed that Pseudomonadota carried the most comprehensive amino acid metabolic network, including a serine and threonine degradation pathway absent from other taxa. Crucially, one Shewanella MAG, designated C3_bin52, harbored 2,488 KEGG orthologs, with more than 10 percent of them tied to amino acid metabolism, including complete biosynthetic pathways for essential and branched-chain amino acids. Genes for branched-chain amino acid transferase (ilvE) and tryptophan synthesis (trpA, trpB) were identified within its repertoire.

The metabolomics data provided the physiological confirmation. Using ultra-high-performance liquid chromatography coupled to high-resolution mass spectrometry, the researchers profiled 947 metabolites in fecal samples and found clear separation between dietary groups. The Sargassum group stood out with 21 up-regulated metabolites, dominated by essential amino acids such as L-valine and L-threonine, the branched-chain amino acid leucine, and derivatives including 5-hydroxy-L-tryptophan and trans-cinnamic acid—a compound with documented antimicrobial activity against fish pathogens. Pathway enrichment confirmed that the Sargassum diet preferentially activated protein digestion and absorption and amino acid biosynthesis, whereas Asparagopsis skewed toward tyrosine and thyroid hormone pathways and Gracilaria toward nucleotide metabolism.

The statistical integration of all three data layers converged on Shewanella as the central hub. Spearman correlation analysis identified 78 significant microbiome-metabolite associations, and Shewanella displayed the highest connectivity, correlating positively with 22 metabolites, including L-valine and the aromatic amino acid derivative 2-hydroxycinnamic acid. A partial least squares path model, with a goodness-of-fit of 0.554, showed that Shewanella abundance was positively and significantly associated with amino acid metabolism (coefficient 0.655), which in turn correlated positively with growth performance (coefficient 0.596). In other words, the data support a causal-style chain: seaweed polysaccharides and free amino acids feed a microbial niche, Shewanella fills it, and its metabolic output enriches the host’s amino acid pool.

The biological plausibility of this axis is reinforced by what is already known about the genus. Shewanella species are metabolically versatile aquatic bacteria capable of dual pyruvate and lactate fermentation, degradation of complex polysaccharides such as alginate via thermostable lyases, and even biosynthesis of health-promoting omega-3 polyunsaturated fatty acids. Probiotic strains of Shewanella putrefaciens have previously been shown to improve growth and disease resistance in farmed fish. In fish-derived strains, roughly 8 percent of coding sequences are devoted to amino acid transport and metabolism—an extraordinary genomic commitment that aligns neatly with the metabolite patterns observed in the carp.

Beyond its mechanistic interest, the study carries practical weight for a rapidly growing industry under pressure to find sustainable alternatives to fishmeal and other conventional feed ingredients. Macroalgae cultivation requires no freshwater, arable land, or fertilizer, making seaweed-supplemented feeds an attractive sustainability proposition. The finding that different seaweeds steer the gut microbiome toward different functional outcomes—Sargassum toward amino acid metabolism and growth, Asparagopsis toward tyrosine pathways and suppression of the opportunistic pathogen Acinetobacter, Gracilaria toward butyrate-producing taxa and nucleotide metabolism—suggests that feed formulators could in principle select macroalgal species to elicit targeted microbial and metabolic effects. The authors caution that the specific functional roles of individual Shewanella species still require direct experimental validation, for example through isolation and gnotobiotic challenge studies. Even so, the work establishes a compelling diet-microbiome-metabolite framework for herbivorous aquaculture species and positions a once-obscure marine bacterium as a potential keystone of fish nutrition—one that farmers may one day cultivate deliberately, simply by choosing the right seaweed.

Subject of Research: Macroalgae supplementation modulates the gut microbiome and amino acid metabolism in grass carp

Article Title: Dietary macroalgae enhances amino acid metabolism via intestinal Shewanella in grass carp (Ctenopharyngodon idella)

Article References: An, X., Niu, S., Al, M. A., Su, E., Chen, L., He, H., Wang, Y., Zhang, S., Yang, Y., Wang, S., Wen, Z., Xu, B., Ming, Y., Zhu, W., Zhao, Z., Wu, K., Yang, Y., Xie, W., He, Z., & Yan, Q. (2025). Dietary macroalgae enhances amino acid metabolism via intestinal Shewanella in grass carp (Ctenopharyngodon idella). Advanced Biotechnology, 3(4), Article 36. https://doi.org/10.1007/s44307-025-00090-8

Image Credits: AI Generated

DOI: 10.1007/s44307-025-00090-8

Keywords: grass carp, macroalgae, gut microbiome, Shewanella, amino acid metabolism, aquaculture, metagenomics, metabolomics, Sargassum hemiphyllum, feed additives, metagenome-assembled genomes, fish nutrition

Biofloc technology, commonly abbreviated as BFT, is essentially a recirculating system built around microbes rather than mechanical filtration. The tanks hold a dense, suspended community of microalgae, autotrophic and heterotrophic bacteria, fungi, ciliates, protozoans, and small zooplankton such as rotifers, copepods, and nematodes, all maintained with minimal or zero water exchange. The central trick is the manipulation of the carbon-to-nitrogen ratio. Fish excrete nitrogenous waste, chiefly ammonia, which is toxic at even modest concentrations. By adding an external carbon source such as molasses, sugar, glucose, wheat flour, or regional agricultural by-products, farmers push the ratio high enough that heterotrophic bacteria dominate. These bacteria assimilate inorganic nitrogen directly into their own cell biomass, converting a pollutant into living feed. The resulting aggregates, the flocs themselves, remain suspended in the water column and are grazed by the cultured animals.

The nutritional payoff is substantial. According to the review, biofloc typically contains 12 to 50 percent protein, 0.5 to 41 percent lipids, 14 to 59 percent carbohydrates, and 3 to 61 percent ash on a dry-weight basis, with the exact profile depending on the carbon source, salinity, and species cultured. Marine bioflocs are especially rich in essential amino acids including valine, lysine, leucine, phenylalanine, and threonine, although they can be deficient in vitamin C, arginine, methionine, and cysteine. Beyond macronutrients, flocs deliver bioactive compounds such as essential fatty acids, carotenoids, chlorophylls, free amino acids, and trace minerals, which support cell membrane integrity, antioxidant defenses, reproduction, and immune function. Researchers cited in the review note that biofloc is a valuable protein source not only for tilapia and prawns but also for mussels, and studies have shown that shrimp raised in biofloc systems accumulate more nitrogen in their biomass than those in conventional cultures.

The consequences for feed economics are significant, because feed is the single largest cost in most aquaculture operations. By recycling organic waste into in-situ microbial protein, BFT reduces dependence on expensive commercial feeds, and the review reports lower feed conversion ratios and higher protein efficiency ratios across numerous trials. In one experiment on Nile tilapia, daily addition of molasses as a fresh carbon source increased growth rates and productivity while cutting costs by 15 percent and raising profitability by 25 percent. Feeding strategy matters too: tilapia fed twice daily under biofloc conditions achieved 100 percent survivability and production of 11.27 kilograms per cubic meter, while reducing labor costs. Because the system also slashes water exchange, it conserves two of aquaculture’s scarcest resources, water and land, making high-density culture feasible for small-scale and resource-limited farmers.

Getting the carbon-to-nitrogen ratio right, however, is a delicate balancing act, and much of the recent literature reviewed by the authors focuses on finding species-specific optima. In stinging catfish, researchers tested ratios of 12, 15, 18, and 21 and found that a ratio of 15 produced the highest protein content and lowest moisture in the fish, with no significant differences in lipid and ash among the higher treatments. In common carp, sugarcane molasses raised the ratio and stimulated bioflocculation and heterotrophic bacterial growth, with a ratio of 19:1 improving water quality and growth, but pushing to 23:1 worsened feed conversion, protein efficiency, and feed intake. Ratios above 20:1 led to accumulation of dissolved salts and settled biomass that destabilized the system. In common carp fed at ratios of 10:1, 15:1, and 20:1, the highest ratio proved optimal for physiological and immune responses as well as growth, underscoring that the ideal value shifts with species, carbon source, and culture conditions.

Water quality dynamics explain why these thresholds matter. As carbon input rises, heterotrophic bacteria proliferate, and the resulting bacterial biomass, aggregated organic matter, and floc particles drive total suspended solids upward. Mineralization of that organic matter releases dissolved ions, raising total dissolved solids as well. Meanwhile, pH, total ammonia nitrogen, and nitrite nitrogen tend to fall as the ratio increases, because bacteria assimilate the nitrogen before it becomes toxic. In trials with Nile tilapia in cement ponds, both sugarcane molasses and wheat flour significantly lowered pH, unionized ammonia, and nitrite compared with controls, while nitrate and suspended solids climbed. Elevated nitrogenous compounds can inhibit nitrification and degrade water quality, so operators must monitor solids and be prepared to remove excess floc, often through settling basins or filtration.

One of the most striking findings synthesized in the review is the immune boost that biofloc microbes appear to provide. Specific microorganisms in the floc community function as natural probiotics, and fish and shellfish raised in these systems show significantly higher phagocytosis rates, nitroblue tetrazolium and myeloperoxidase activity, alternative complement pathway activity, total immunoglobulin levels, lysozyme activity, and antioxidant enzymes such as superoxide dismutase and catalase compared with animals in conventional systems. The practical result is greater resistance to major pathogens including Aeromonas hydrophila, Vibrio harveyi, Streptococcus agalactiae, and Edwardsiella tarda. Hematological studies reinforce the picture: genetically improved farmed tilapia in biofloc systems showed elevated serum glutathione peroxidase and lysozyme activity, common carp given cane molasses showed markedly reduced stress, and tilapia reared with zero water exchange displayed increased red blood cell counts and hemoglobin alongside reduced cortisol, liver enzymes, and urea, indicating improved welfare and homeostasis.

The microbial ecology underpinning these benefits is complex and still being mapped. Floc-forming microbes secrete extracellular polymeric substances that glue particles together and stabilize the aggregates, while nitrifying bacteria handle chemoautotrophic oxidation of ammonia, and grazers such as rotifers and protozoans recycle nutrients and enrich the floc as a food source. Systems are typically classified as green water biofloc, exposed to natural light and driven by both algal and bacterial processes, or brown water biofloc, run in closed environments where bacteria alone regulate water chemistry. Community composition shifts with the carbon source, salinity, and cultured species, and phytoplankton contribute by absorbing excess nutrients and producing dissolved oxygen. Managing this living suspension, rather than sterilizing it, is the fundamental philosophical shift that distinguishes biofloc from conventional intensive culture.

The technology is not without drawbacks, and the review is candid about them. Continuous, vigorous aeration is required to satisfy the biological oxygen demand of both animals and microbes, driving up energy consumption and operational costs. High water temperatures can favor pathogenic microbial growth, and accumulated organic load degrades water quality if solids management lapses. Consumer acceptance of fish raised in microbial floc also remains an open question that the authors say must be addressed ethically and transparently. Current applications concentrate on herbivorous, detritivorous, and bottom-dwelling species such as tilapia and shrimp; extending the approach to carnivorous fish will require redesigned carbon dosing and system architecture. The authors recommend optimizing biofloc concentrations, compartmentalizing system components for better control, and investing in farmer training and financial support to widen adoption.

Even with those caveats, the trajectory is clear. Biofloc technology aligns economic self-interest with environmental stewardship, turning the aquaculture industry’s most stubborn waste problem into a protein asset while cutting water use, land requirements, and antibiotic dependence. For policymakers and investors seeking responsible aquaculture growth, and for smallholder farmers in water-scarce regions who cannot afford conventional recirculating systems, the review positions biofloc as a practical bridge between rising global fish demand and the ecological limits of the planet, provided that research continues to refine carbon management, microbial community control, and species-specific system design.

Subject of Research: Biofloc technology for sustainable aquaculture: nutrition, water quality, and system efficiency

Article Title: The role of biofloc technology in sustainable aquaculture: nutritional insights and system efficiency

Article References: Yadav, N. K., Paul, S., Patel, A. B., Mahanand, S. S., Biswas, P., Choudhury, T. G., Baidya, S., & Meena, D. K. (2025). The role of biofloc technology in sustainable aquaculture: nutritional insights and system efficiency. Blue Biotechnology, 2(1), Article 7. https://doi.org/10.1186/s44315-025-00025-x

Image Credits: AI Generated

DOI: 10.1186/s44315-025-00025-x

Keywords: biofloc technology, aquaculture, sustainability, carbon-nitrogen ratio, water quality, fish nutrition, tilapia, shrimp farming, microbial protein, feed conversion ratio, fish immunity, wastewater recycling

The appeal of nanomaterials lies in physics rather than chemistry alone. When matter is reduced to dimensions below roughly 100 nanometers, quantum effects and an enormous surface-area-to-volume ratio transform its behavior, dramatically enhancing electrical, magnetic, optical, and catalytic properties compared with the same material in bulk form. In water treatment, this translates into far greater capacity to capture and degrade contaminants. Aquaculture effluent is a complicated cocktail: total suspended solids, fecal matter and uneaten feed, phosphorus and nitrogen, ammonia, therapeutic drugs, and antifouling chemicals. The review identifies four principal classes of nanomaterials for tackling this burden: metal-containing nanoparticles, carbonaceous nanomaterials such as carbon nanotubes, zeolites, and dendrimers, each exploiting distinct mechanisms of adsorption, reduction, or catalytic oxidation.

Silver nanoparticles have emerged as the most intensively studied disinfection agents. Their antimicrobial power stems from a multi-pronged attack: the particles adhere to bacterial cell walls, penetrate them, and alter permeability, while silver ions interact with sulfur- and phosphorus-containing cellular components, inactivate enzymes by binding thiol groups, disrupt DNA replication, and trigger the release of reactive oxygen species. Laboratory studies cited in the review found that nanosilver at just 1 milligram per liter can suppress roughly 80 percent of a microbial population. Crucially, the authors caution against dosing water directly, since silver can bioaccumulate in cultured fish destined for human consumption. A safer strategy, they suggest, is coating filtration equipment with silver nanoparticles, allowing disinfection without exposing the animals themselves to the metal.

Nano zero-valent iron particles represent a second workhorse of nanoscale water remediation. These tiny iron particles act as powerful reducing agents, transferring electrons from their surfaces to pollutants and converting them into less harmful forms. Their redox activity, combined with adsorption and precipitation, has been harnessed to remove halogenated organic compounds, dyes, phenols, heavy metals, phosphates, and nitrates. One striking example is the treatment of hexavalent chromium, a highly carcinogenic contaminant: the iron nanoparticles reduce it to chromium(III), which precipitates as a far more stable hydroxide. Researchers have also documented effective lead removal using stabilized zero-valent iron, though concerns about the persistence of these particles in treated systems have driven efforts to immobilize them within porous support materials.

Zinc and iron oxide nanoparticles round out the water-treatment toolkit. Zinc oxide nanoparticles combine strong photocatalytic and oxidative capabilities with low cost and environmental compatibility, and their performance can be boosted by doping with metal ions, semiconductors, or reduced graphene oxide. Comparative studies found that zero-valent zinc outperformed iron, aluminum, and nickel nanoparticles in degrading octachlorodibenzo-p-dioxin, one of the most notorious persistent organic pollutants. Magnetic iron oxides, including magnetite, maghemite, and hematite, serve as efficient sorbents for heavy metals; magnetite nanosorbents have shown a maximum adsorption capacity of 36 milligrams of lead per gram of material, and their superparamagnetism allows easy recovery from treated water. Titanium dioxide, meanwhile, acts as a broad-spectrum photocatalyst, generating reactive oxygen species under even low ultraviolet light to destroy gram-positive and gram-negative bacteria, fungi, and viruses. In China, a sintered ceramic nanomaterial called Nano-863, prized for its light absorption and heat resistance, is already being used commercially to improve water quality for shrimp farming and to curb algal blooms.

Beyond water quality, the review highlights a less obvious frontier: fish reproduction. Captive fish often suffer reproductive dysfunction, and conventional hormonal therapies to induce spawning are undermined by the short half-life of gonadotropin-releasing hormone, which is rapidly degraded by enzymes in the pituitary, kidney, and liver. Repeated injections work but stress the animals. Nanoparticle carriers offer an elegant workaround. In common carp, researchers conjugated the hormone LHRH to chitosan nanoparticles and chitosan-gold nanoparticles, achieving sustained hormone release and fertilization rates of 87 percent and 83 percent respectively, compared with 74 percent in controls. In walking catfish, chitosan nanoparticles loaded with pheromones kept serum hormone levels elevated far longer than injections. Oral delivery of GnRHa via chitosan nanoparticles in goldfish, fed every three days over 40 days, prolonged hormone elevation and significantly increased egg diameter, while PLGA nanoparticles loaded with aromatase inhibitors have been used to produce monosex populations of tilapia and guppies.

Feeding efficiency is another target. Aquafeed is perishable, and its water-soluble components leach into ponds, driving pollution and nutrient loss while inflating costs. Nanotechnology addresses this by encapsulating active ingredients, protecting them until they reach the fish’s intestine. Nanoparticle-enriched feeds have demonstrably improved growth, survival, feed conversion ratio, specific growth rate, weight gain, blood parameters, and immune responses. Selenium nanoparticles enhanced growth and larval development in Nile tilapia, Asian sea bass, and gilthead sea bream at species-specific doses; iron nanoparticles upregulated growth-related genes in goldfish and improved muscle protein in catfish; and chitosan nanoparticles boosted immunity and survival in tilapia, common carp, and giant tiger prawns.

Disease management may be where nanotechnology delivers its most consequential impact. Antibiotic resistance is now documented throughout aquaculture, with tetracycline-, streptomycin-, and erythromycin-resistant Aeromonas hydrophila isolated from tilapia farms, alongside resistant strains of Staphylococcus aureus, Vibrio, Yersinia ruckeri, and Edwardsiella. Nanoparticles offer an alternative: engineered antibacterial surfaces, nanosensors that detect pathogens in water, and nano-encapsulated medicines delivered through feed. Diagnostic applications are already proving their worth. Magnetic nanoparticles coated with antibodies change color from red to blue when they bind viral antigens, enabling rapid detection of nervous necrosis virus in groupers, while unmodified gold nanoparticles have been used in similar colorimetric assays for spring viremia of carp and koi herpesvirus. Electrical nanosensors can now detect a single virus particle, and wireless tracking nanosensors permit individual fish health monitoring through data analysis.

Nanovaccines tackle the central dilemma of fish immunization: oral vaccines are destroyed by gastric digestion, while injections stress the animals. Polymer and lipid nanoparticles shield antigens from degradation in the gastrointestinal tract and deliver them intact to provoke mucosal, humoral, and cellular immunity. Challenge trials with nanovaccines against Listonella anguillarum succeeded in Asian carp and rainbow trout, chitosan-based oral nanovaccines protected tilapia against columnaris disease, and chitosan-coated membrane vesicles strengthened immunity against Piscirickettsia salmonis in zebrafish. Biosensors extend this precision medicine approach to physiology itself: enzyme-based immunosensors measure cortisol in fish blood to quantify stress, ranking stressors from air exposure to nitrite, while wireless implantable sensors transmit real-time blood glucose readings from swimming fish to receivers on shore.

The review is candid about the risks. Because of their minute size, nanoparticles readily cross cell membranes, and their chemical reactivity generates reactive oxygen species and free radicals that can cause inflammation, protein damage, and DNA deterioration. Silver nanoparticles smaller than 10 nanometers inflicted significantly more kidney and gill damage in rainbow trout than particles exceeding 35 nanometers, copper nanoparticles harmed liver, brain, and gill function in Mozambique tilapia, and zero-valent iron proved more toxic to embryonic medaka than to adults, underscoring the heightened vulnerability of early life stages. Nano waste, the authors warn, constitutes a novel form of pollution requiring careful tracking through food chains. Regulatory frameworks, including World Health Organization guidelines on manufactured nanomaterials, remain a work in progress, and the authors call for sustained investment, public-private partnerships, and technology transfer to developing nations. With emerging tools such as multi-omics toxicology and personalized fish health assessment on the horizon, they conclude that responsible integration of nanotechnology could help aquaculture meet global protein demands without compromising the ecosystems on which it depends.

Subject of Research: Applications of nanotechnology in sustainable aquaculture and fish health management

Article Title: Interventions of nanotechnology-based applications as a novel tool for sustainable aquaculture and fish medicines

Article References: Riyaz, R., Iqbal, G., Gargotra, P., & Ganie, P. A. (2025). Interventions of nanotechnology-based applications as a novel tool for sustainable aquaculture and fish medicines. Blue Biotechnology, 2(1), Article 12. https://doi.org/10.1186/s44315-025-00034-w

Image Credits: AI Generated

DOI: 10.1186/s44315-025-00034-w

Keywords: nanotechnology, aquaculture, nanoparticles, water treatment, fish health, nanovaccines, nanosensors, antibiotic resistance, fish nutrition, nanotoxicology, sustainability, chitosan

The core premise of nutrigenomics is deceptively simple. Nutrients do not merely fuel a fish; they act as chemical signals that switch genes on and off, reshaping metabolism, immunity, and growth at the molecular level. The field emerged in the late 1990s at the intersection of nutritional science and genomics, and it has since migrated from human medicine into livestock and, more recently, into aquaculture. Farmed fish are an especially attractive target because their diets are entirely controlled by producers. If researchers can identify which genes respond to which dietary ingredients, they can in principle design feeds that maximize feed conversion efficiency, strengthen disease resistance, and even alter the nutritional profile of the fillet that reaches the consumer’s plate. The retracted review argued that this approach could transform aquaculture into a precision discipline, where rations are tailored to the genome of each species rather than formulated by trial and error.

The technological engine behind this vision is a battery of omics tools. Whole genome sequencing has supplied reference assemblies for major farmed species, while RNA sequencing, or transcriptomics, allows scientists to measure which genes are active in fish fed different diets, exposing the molecular fingerprints of each ration. Proteomics extends the analysis to the proteins those genes produce, and metabolomics captures the biochemical end products of metabolism, closing the loop between gene and physiology. Perhaps the most disruptive entry is CRISPR gene editing, which enables researchers to deliberately disable or modify genes suspected of governing feed efficiency, fatty acid synthesis, or stress tolerance, then observe the consequences. The review highlighted these tools as the foundation for identifying the genetic pathways that control how fish digest proteins, metabolize lipids, and mount immune responses, turning what was once an opaque black box into an experimentally tractable system.

Among the nutritional pathways receiving the most attention, lipid metabolism stands out. Lipids are a principal energy source for many fish, and the genes governing fatty acid synthesis, elongation, and desaturation determine whether a farmed fish can build health-promoting omega-3 fatty acids such as EPA and DHA from plant-based feed ingredients. The review cited work on hybrid grouper showing that high-lipid diets cause hepatic fat accumulation and that bile acids modulate this process. Carbohydrate metabolism presents a parallel puzzle: carnivorous fish express low levels of amylase and glucokinase and therefore handle starch poorly. A single-nuclei RNA sequencing study of largemouth bass fed high-carbohydrate diets revealed disturbed hepatic energy metabolism and activation of oxidative stress and liver fibrosis pathways, while whole genome resequencing combined with RNA sequencing linked genes such as fabp6, lpcat2, pla2g1b, and pentose phosphate pathway genes to growth performance under carbohydrate-rich, thermally fluctuating conditions.

Species-specific findings form the empirical backbone of the field. In Atlantic salmon, research has concentrated on lipid metabolism and immune function, including the identification of genes involved in omega-3 biosynthesis and pathogen resistance. One frequently cited study replaced fish oil with vegetable oil in salmon diets and used liver transcriptomics to track the consequences: genes for fatty acid biosynthesis, inflammation, and oxidative stress, including fasn, cox2, and pparα, shifted expression, signaling a fundamental rewiring of lipid handling. Tilapia has served as a model for testing plant-based alternative feeds on nutrient utilization and growth, while catfish studies have uncovered nutrigenomic pathways tied to hypoxia tolerance and feed efficiency, informing breeding programs for hardier strains. Carp, with their natural talent for carbohydrate metabolism, are being studied as candidates for sustainable plant-based feeding, a trait that could ease pressure on wild-capture fisheries that supply fishmeal.

The larval stage of farmed fish has emerged as a particularly sensitive window where nutrition leaves lasting genomic marks. Larvae are typically reared on live feeds such as rotifers and artemia, enriched with phospholipids, fatty acids, and micronutrients that support growth, survival, and disease resistance. Researchers formulating a microdiet of 22 percent lipid and 52 percent protein for pike silverside larvae found differential gene expression and overexpression of apoptotic, DNA damage repair, and oxidative stress genes, which correlated with suboptimal growth and survival, prompting a recommendation to reduce lipid content. De novo transcriptomic sequencing of tropical gar embryos and larvae identified nutrigenomic markers spanning cell cycle, digestion, muscle development, and behavioral genes. In Atlantic cod larvae, RNA sequencing and qPCR revealed that fast-moving copepod prey stimulated swimming activity, boosting glycolysis and oxidative phosphorylation in muscle cells but also elevating reactive oxygen species, a burden that prey nutritional quality must counterbalance. Adding alpha lipoic acid to pike silverside microdiets improved larval survival and feed efficiency by modulating mitochondrial biogenesis and DNA repair.

Beyond growth, nutrigenomics is being deployed to armor fish against disease through diet rather than drugs. Functional feeds enriched with probiotics, prebiotics, or plant-derived bioactive compounds have been shown to reshape the expression of immune-related genes. In rainbow trout, dietary supplementation with the probiotic Lactobacillus rhamnosus upregulated genes governing gut barrier function, including mucins and tight junction proteins, alongside immune genes such as cytokines and toll-like receptors. In Pacific white shrimp, vitamin C supplementation upregulated antioxidant defenses, including sod and cat, and immune genes including toll-like receptors and penaeidins, increasing resistance to the pathogenic bacterium Vibrio parahaemolyticus. Selenium studies in rainbow trout demonstrated that organic selenomethionine significantly upregulated antioxidant genes such as gpx1 and sod2, reducing markers of oxidative stress, while laminarin, a bioactive polysaccharide from brown algae, altered immune gene expression in abalone. Microalgal diets rich in Isochrysis galbana upregulated energy metabolism genes in Pacific oysters, and vitamin C-enriched diets in tilapia boosted SOD and CAT expression while dialing down the stress marker HSP70.

The human-health dimension of this research extends to biofortification and contaminant control. Because omega-3 fatty acids reduce cardiovascular risk and support cognitive function, researchers are pursuing fish strains genetically optimized for EPA and DHA production, including transgenic strategies that stimulate desaturase gene expression. Nutrigenomic approaches may also identify genes governing the metabolism and detoxification of heavy metals and pesticides, opening a route to fish lines that accumulate fewer contaminants and meet stricter food safety standards. The review even sketched a vision of regionally tailored products, fish engineered or selectively bred to carry more selenium or vitamin A precursors, addressing specific nutrient deficiencies in particular populations. By contrast, plant protein substitution is not without molecular cost: in zebrafish fed soybean meal, transcriptomics revealed altered lipid homeostasis through genes such as ppara, fabp2, mttp, and cyp7a1, along with mild intestinal inflammation marked by elevated pro-inflammatory cytokines.

The retraction of this particular review does not settle any of these scientific questions, but it does underscore the scrutiny that fast-moving fields attract, and it coincides with a candid discussion of the field’s unresolved problems. The review itself acknowledged that RNA sequencing and CRISPR remain expensive, that bioinformatics capacity is a bottleneck for many aquaculture facilities, and that genetically modified fish raise public acceptance concerns, biodiversity risks, and ecological hazards if transgenic animals escape and interbreed with wild populations. Looking forward, it pointed to artificial intelligence and machine learning for predicting gene-nutrient interactions and optimizing feed formulas, multi-omics integration for holistic views of fish biology, and cross-sector partnerships to build affordable technologies and responsible regulatory frameworks. Readers should consult the publisher’s retraction notice before relying on any claim from the withdrawn article, but the underlying research program it surveyed, from copepod-fed cod larvae to CRISPR-edited salmon, continues to advance in the peer-reviewed literature, carrying the promise of seafood that is healthier for people and gentler on the planet.

Subject of Research: Fish nutrigenomics and its application to sustainable aquaculture nutrition

Article Title: RETRACTED ARTICLE: Fish nutrigenomics: unravelling the genetic code for sustainable aquaculture and improved nutritional benefits

Article References: Iqbal, G., Wani, M. N., Piyushbhai, M. K., Dar, S. A., & Sharma, A. (2025). RETRACTED ARTICLE: Fish nutrigenomics: unravelling the genetic code for sustainable aquaculture and improved nutritional benefits. Blue Biotechnology, 2(1), Article 19. https://doi.org/10.1186/s44315-025-00043-9

Image Credits: AI Generated

DOI: 10.1186/s44315-025-00043-9

Keywords: nutrigenomics, aquaculture, fish nutrition, genomics, CRISPR, RNA sequencing, omega-3 fatty acids, feed efficiency, disease resistance, transcriptomics, sustainable food, retraction

The research, led by Kedar Nath Mohanta of the ICAR-Central Institute of Fisheries Education in Mumbai, together with colleagues at the ICAR-Central Institute of Freshwater Aquaculture and the ICAR-Central Inland Fisheries Research Institute, set out to answer a deceptively simple question: how much protein, lipid, and carbohydrate should go into the feed of pengba fingerlings? The stakes are high because feed is the single largest expense in fish farming, often accounting for more than half of variable costs in traditional systems and up to 60 percent in feed-intensive operations. Getting macronutrient levels wrong means wasting money and, worse, polluting water with excess nitrogen while producing slower-growing fish. Getting them right means faster growth, cleaner water, and better economics for a species whose captive propagation could ease pressure on wild populations.

The team ran three experiments in sequence, each building on the last. In the first, 90-day trial, fingerlings with an average body weight of 0.83 grams were stocked into flow-through fiberglass tanks at 15 fish per tank, with water flowing at 0.5 liters per minute. Nine semi-purified diets were tested in a 3-by-3 factorial design combining three protein levels, 30, 35, and 40 percent, with three lipid levels, 6, 8, and 10 percent. The fish were fed to apparent satiation twice daily, unconsumed feed and waste were siphoned off every morning, and biomass was measured every fortnight. Water quality stayed firmly within ideal rearing ranges throughout, with temperatures of roughly 28 to 30 degrees Celsius, dissolved oxygen between 7.87 and 8.65 milligrams per liter, and total ammonia below 0.07 milligrams per liter.

The result was a clear winner. Fingerlings fed the diet containing 35 percent protein and 8 percent lipid showed significantly higher weight gain and specific growth rate, along with a significantly lower feed conversion ratio, than any other combination. Survival was uniformly high, with no mortality recorded across treatments, which the researchers note confirms the diets themselves, not disease or handling stress, drove the differences in growth. Statistical analysis revealed a notable interaction between protein and lipid: raising lipid from 6 to 8 percent improved performance at every protein level, but pushing it to 10 percent offered no further benefit. Across the board, 35 percent protein emerged as the sweet spot, and second-order polynomial regression sharpened the estimate further, placing the optimal protein requirement between 35.49 and 35.83 percent and the optimal lipid requirement between 8.37 and 8.43 percent.

Why does more protein not simply mean more growth? The explanation lies in energy metabolism. Protein is the costliest macronutrient in aquafeed and should ideally be reserved for building tissue, repairing muscle, and synthesizing enzymes rather than being burned for fuel. When dietary protein exceeds what a fish needs for growth, it is catabolized as an energy source, an inefficient and polluting outcome that also increases nitrogenous waste. Lipids help solve this problem through the protein-sparing effect: fat provides roughly 9 kilocalories per gram, more than double the energy of protein or carbohydrate, so adequate dietary lipid allows the fish to oxidize fat for energy and preserve amino acids for growth. But the effect has a ceiling. Beyond 8 percent lipid in this species, excess fat begins to interfere with digestion, disrupt fatty acid synthesis, and suppress feed intake, ultimately slowing growth, a pattern previously documented in common carp, catla, and the Australian short-fin eel.

With protein and lipid optimized, the second experiment turned to carbohydrate, the cheapest energy source in any fish diet. Six semi-purified diets were formulated with carbohydrate levels ranging from 20 to 45 percent, while protein and lipid were held at the newly determined optima of 35 and 8 percent. Slightly larger fingerlings, averaging 1.60 grams, were reared in 70-liter flow-through tanks for 60 days. Once again the regression curves told a coherent story: fish receiving 40 percent carbohydrate achieved significantly superior weight gain, specific growth rate, and feed conversion, with polynomial analysis bracketing the optimum between 39.61 and 40.23 percent. This finding positions pengba among the carbohydrate-efficient omnivorous carps, a group that includes common carp, tilapia, and mullet, species known to convert starch into energy at levels their carnivorous counterparts cannot tolerate. Every carbohydrate calorie that displaces dietary protein improves both the economics of the feed and the quality of the water, since less protein catabolized means less nitrogen excreted into culture systems.

The third experiment moved from purified ingredients to the practical question that matters most to farmers: which plant protein sources should go into a real-world feed? Five iso-nitrogenous, iso-lipidic, and iso-caloric diets, each containing 35 percent protein, 8 percent lipid, and 4.0 kilocalories per gram of gross energy, were built around different oil cakes as primary protein sources. Diet D-1 used soybean meal, D-2 groundnut oil cake, D-3 mustard oil cake, D-4 sesame oil cake, and D-5 mahua oil cake, a non-conventional ingredient pressed from the seeds of Bassia latifolia, a tree abundant across rural India. Vegetable oil adjusted lipid levels where needed, and de-oiled rice bran supplied the carbohydrate backbone. The 90-day trial used 0.42-gram fingerlings stocked in cement tanks and fed twice daily at 5 percent of body weight.

Mahua oil cake emerged as the unexpected champion. Fish fed the D-5 diet, which combined mahua oil cake with soybean and groundnut oil cakes, recorded significantly higher weight gain and protein efficiency ratio and a lower feed conversion ratio than any alternative. The result aligns with earlier work showing that mahua oil cake, especially in fermented form, enhances growth and immune function in rohu fingerlings, boosting phagocytic activity and digestive enzyme performance. Its favorable showing here is commercially significant because mahua is cheaper and more locally available than imported fish meal, which typically contains 60 to 72 percent protein and dominates high-quality aquafeeds. Soybean meal, with 44 to 48 percent protein and a reasonably balanced amino acid profile, remains a workhorse ingredient but requires processing to neutralize anti-nutritional factors. Blending several oil cakes appears to balance amino acid profiles while keeping costs down.

The authors are careful to frame these numbers as a foundation rather than a finish line. Future studies, they write, should probe the physiological and metabolic responses of pengba by measuring digestive enzyme activities, metabolic profiles, and stress biomarkers, and should extend into molecular territory, examining the expression of genes governing nutrient metabolism, growth regulation, and stress adaptation. Such mechanistic work would explain why the fish performs best on a diet that is, by terrestrial livestock standards, carbohydrate-heavy. It would also help nutritionists fine-tune feeds across life stages, since fingerling requirements rarely match those of broodstock or market-size fish.

For now, the practical implications are immediate and encouraging. A feed containing roughly 35 percent protein, 8 percent lipid, and 40 percent carbohydrate, built on a mahua-soybean-groundnut oil cake blend, gives hatcheries and grow-out farmers a validated, cost-effective starting formulation for pengba. Because the species is endangered, expanding its culture does double duty: it supplies a premium product to a hungry market while reducing fishing pressure on the wild population in Loktak Lake and beyond. Captive breeding of pengba has been feasible for years thanks to induced spawning with hormones; what has been missing is a scientific basis for feeding the fish efficiently at scale. With this study, that gap has been closed, and one of India’s most culturally cherished carps now has a dietary prescription backed by rigorous, replicated data.

Subject of Research: Optimization of dietary macronutrient requirements and plant-based protein ingredients for rearing endangered pengba carp (Osteobrama belangeri) fingerlings

Article Title: Optimization of macro-nutrient requirements and different protein-based ingredients for pengba, Osteobrama belangeri (Valenciennes, 1844) fingerlings

Article References: Mohanta, K. N., Khalasi, Y., Prakash, P., Kumari, R., Chandan, N. K., & Meena, D. K. (2025). Optimization of macro-nutrient requirements and different protein-based ingredients for pengba, Osteobrama belangeri (Valenciennes, 1844) fingerlings. Blue Biotechnology, 2(1), Article 27. https://doi.org/10.1186/s44315-025-00042-w

Image Credits: AI Generated

DOI: 10.1186/s44315-025-00042-w

Keywords: pengba, Osteobrama belangeri, aquaculture, fish nutrition, macronutrient requirements, feed formulation, protein requirement, lipid, carbohydrate, mahua oil cake, endangered species, carp farming

Compensatory growth is the accelerated phase of growth that follows a period of food deprivation when adequate nutrition is restored. During re-feeding, fish commonly exhibit hyperphagia, an elevated appetite, along with improved feed conversion efficiency and enhanced nutrient utilization, allowing them to partially or fully recover the growth lost during starvation. The magnitude of this recovery depends on the species, the severity and duration of restriction, environmental conditions, and the structure of the feeding regime itself. While the phenomenon has been documented extensively in laboratory settings across carp, tilapia, seabream, sturgeon, and crustaceans, field data from real pond ecosystems, where plankton and other natural food organisms contribute meaningfully to fish nutrition, have remained scarce. The new study, published in Blue Biotechnology, addresses that gap directly by testing cyclic restriction protocols across an entire ten-month production cycle under commercial-style pond conditions.

The experimental design was deliberately rigorous. Twelve earthen ponds of 0.04 hectares each were prepared according to the standard pre-stocking protocols of ICAR-CIFA, including drying, liming, and fertilization, and stocked with rohu fingerlings at 7,500 fish per hectare with three replicate ponds per treatment. Fertilization followed a uniform fifteen-day schedule using urea, single superphosphate, and composted cow dung to sustain natural food production identically across all ponds, ensuring that any differences among treatments could be attributed to the feeding regime rather than variations in pond productivity. Fish received a sinking pelleted diet formulated from groundnut oil cake, sesame oil cake, and rice bran, delivering 25.63 percent crude protein, 7.26 percent ether extract, and a digestible energy of 17.08 megajoules per kilogram, and were fed at 1.5 to 3.0 percent of body weight depending on size, with monthly sampling to adjust rations.

Three cyclic restriction schedules were tested against a continuously fed control over the ten-month trial. The T-1 protocol combined two months of feeding, one month of starvation, one month of re-feeding, a further month of starvation, and five months of re-feeding. T-2 extended the first starvation to two months and shortened the final re-feeding to four months, while T-3 stretched the initial deprivation to three months with only three months of re-feeding at the end. The outcomes diverged sharply. T-1 fish reached a final weight of 662.61 grams and a production of 5,494 kilograms per hectare, statistically indistinguishable from the control and actually representing approximately 4.6 percent greater weight gain and about nine percent higher fish production relative to the control, despite the lower feed input. In contrast, T-2 and T-3 achieved only partial compensation of 81.88 percent and 76.28 percent respectively, with significantly reduced final weights and yields.

Survival ranged from 83.55 to 92.11 percent and did not differ significantly among treatments, indicating that even the harshest restriction schedule remained within the physiological tolerance of the species. Apparent feed conversion ratio and protein efficiency ratio likewise showed no significant differences, though the highest specific growth rate was recorded in the moderate restriction group. Perhaps most striking were the nutrient retention results: protein productive value and lipid productive value were both significantly higher in all restricted feeding groups than in the control, signaling that restricted fish converted dietary protein and lipid into body tissue with markedly greater efficiency during re-feeding. Effect sizes for the key growth variables were enormous, with partial eta-squared values between 0.94 and 0.99, meaning the feeding regime accounted for nearly all of the variance in growth outcomes, a statistical signal the authors describe as biologically as well as statistically meaningful.

The digestive physiology data illuminate the mechanism behind the recovery surge. Protease and lipase activities in the intestinal tissue were significantly higher in the control and T-1 groups than in the longer-restriction treatments, with effect sizes exceeding 0.90. Elevated protease activity in T-1 suggests that moderate deprivation primes the digestive system for accelerated protein digestion once food returns, a well-documented adaptive response in fish recovering from fasting. Conversely, the suppression of both enzymes in T-2 and T-3 reflects the down-regulation of gastrointestinal function during prolonged starvation, when limited substrate availability forces the gut into a metabolically conservative state that cannot be instantly reversed when feeding resumes, ultimately constraining the speed and completeness of growth recovery.

Blood chemistry added a stress dimension to the picture. Haemoglobin concentrations did not differ significantly among groups, indicating that none of the feeding regimes compromised the fish’s oxygen-carrying capacity or hematological health. Blood glucose, however, told a sharper story. Levels were significantly lower in the control and T-1 fish than in T-2 and T-3, and elevated glucose is widely recognized as a physiological stress marker in fish, reflecting enhanced gluconeogenesis and the mobilization of endogenous energy reserves during extended fasting. The authors argue that blood glucose therefore serves as a sensitive indicator of nutritional stress severity under cyclic feeding regimes, and the lower glucose values in the moderate restriction group point to better metabolic adaptation and homeostatic stability.

Carcass composition shifted in revealing ways. Dry matter and crude protein were highest in the T-2 group, and crude lipid rose in all restricted treatments, with the greatest accumulation in the longest-restricted fish. This pattern is consistent with the physiology of recovery: during starvation, fish burn stored glycogen, lipid, and eventually protein to maintain essential metabolism, and during re-feeding, anabolic pathways sweep nutrients into tissue storage with unusual efficiency. Yet the increased protein and lipid deposition in T-2 and T-3 did not translate into superior production, a finding the researchers emphasize as a caution against reading improved nutrient retention alone as evidence of successful feeding management. Tissue deposition, however efficient, cannot compensate for the somatic growth lost to prolonged deprivation.

The practical implications extend well beyond the experimental ponds. Because rohu is cultured extensively in composite carp farming systems across India and beyond, a feeding schedule that maintains full productivity while trimming supplemental feed by roughly nine percent carries substantial economic weight in an industry where feed costs dominate budgets. The savings compound further when reduced feeding labor and lower nutrient loading into pond water are considered. The authors note that their apparent feed conversion ratios excluded the nutrient contribution of plankton, which was assumed equivalent across uniformly fertilized ponds, and they recommend validation in composite culture, integrated multi-trophic aquaculture, recirculating systems, and biofloc-based setups. Broader digestive enzyme profiling and gut morphology studies would also strengthen the mechanistic picture. Still, the core message is clear: in fertilized pond aquaculture, the strategy that wins is not maximum feeding but precisely timed feeding, letting a fish’s own compensatory biology do a measurable share of the work.

Subject of Research: The effects of cyclic feed restriction and re-feeding on compensatory growth, nutrient utilization, digestive enzyme activity, and physiology of Labeo rohita cultured in fertilized ponds.

Article Title: Effects of feed restriction and refeeding on compensatory growth of Labeo rohita in fertilized ponds

Article References: Mohanta, K. N., Khalasi, Y., Prakash, P., Kumari, R., & Chandan, N. K. (2026). Effects of feed restriction and refeeding on compensatory growth of Labeo rohita in fertilized ponds. Blue Biotechnology, 3(1), Article 12. https://doi.org/10.1186/s44315-026-00063-z

Image Credits: AI Generated

DOI: 10.1186/s44315-026-00063-z

Keywords: compensatory growth, Labeo rohita, feed restriction, aquaculture, pond culture, carp, nutrient utilization, digestive enzymes, refeeding, fish nutrition, feed conversion ratio, Blue Biotechnology