The context for the research is a global aquaculture system under strain. Fish provide the primary source of animal protein for many of the world’s poorest people, and demand has surged from roughly forty million tons in 2000 to more than ninety million tons by 2011, driven by population growth. That pressure has contributed to declining aquatic biodiversity in natural waters, pushing production toward farming. Fish farming itself is growing at about seven percent annually worldwide, and in Guinea’s forest region, rice-fish farming systems centered on species such as the African catfish Clarias gariepinus, Heterobranchus isopterus, and Nile tilapia have expanded considerably over the past decade. Yet the sector’s contribution remains limited by a critical bottleneck: the larval and fry rearing phase, where carnivorous young catfish require live prey or costly exogenous feed that rural producers often cannot access year-round.

The research team set out to answer a deceptively simple question: which organic fertilizer produces the most nutritious bloodworms? In September 2023, at an experimental site at the University of N’Zerekore, the researchers installed twenty-four rectangular ponds, each roughly one cubic meter, exposed to open air. Each pond received twenty-five cubic decimeters of a sand and gravel substrate, forty liters of borehole water, and an immediate application of fertilizer at a dose of 140 grams per cubic decimeter of substrate. Four fertilizers were tested: cow dung, rabbit droppings, poultry droppings, and pig manure. Three days after fertilization, the ponds were seeded with phytoplankton-rich pond water filtered through a 100-micrometer sieve to exclude unwanted macroinvertebrates, and three days later the ponds received an initial stocking of Chironomus sp larvae at a density of ten individuals per cubic decimeter of substrate. Mosquito netting covered the ponds to keep predators out.

The results on production density were striking. Rabbit droppings yielded the highest density of Chironomidae at approximately 2,797 individuals per cubic decimeter, followed by cow dung at 2,657, pig dung at 2,473, and poultry droppings at 2,432 individuals per cubic decimeter. Estimated biomass followed a slightly different ranking, with cow dung producing 835.12 milligrams per cubic decimeter and rabbit droppings 786.91, compared with 774.18 for poultry droppings and 723.69 for pig dung, differences the authors report as highly significant. The researchers attribute the elevated densities to the mono-specific nature of their cultures, which outperformed the multi-specific production systems described in earlier studies. Physicochemical monitoring with a multiparameter probe revealed that temperature and pH remained stable across treatments, while conductivity, total dissolved solids, and salinity were elevated in the rabbit and poultry manure ponds, likely reflecting the rich organic matter content of those fertilizers.

Nutritional analysis, however, is where the study delivers its most consequential findings. Using freeze-drying, Kjeldahl protein determination, incineration for ash content, and HPLC-based vitamin assays performed at an ISO 17025-accredited laboratory in Benin, the team quantified the bromatological profile of larvae from each fertilizer treatment. Chironomidae raised on poultry droppings contained the most crude protein at 26.80 percent, followed by rabbit droppings at 22.98 percent, pig manure at 20.48 percent, and cow dung at 17.57 percent. A correspondence factor analysis, whose two axes explained nearly 99.90 percent of the variance, cleanly separated the treatments: rabbit, poultry, and pig manure larvae clustered with protein, vitamins, organic matter, and dry matter, while cow dung larvae associated with ash, or mineral content. The larvae also carried measurable fat-soluble vitamins A, D, and E, ranging from 0.21 to 0.52 micrograms per 100 grams, and water-soluble vitamins B1 and B2 between 0.26 and 0.6 micrograms per 100 grams.

With the nutritional profiles in hand, the researchers turned to the ultimate test: feeding trials with African catfish fry. Catfish larvae were first raised on zooplankton for thirteen days post-hatching to reach fry size, starting the experiment at an average weight of just 3.06 milligrams. Fifteen circular above-ground ponds each received 150 fry, which were fed four times daily, at eight in the morning, noon, four in the afternoon, and eight in the evening, for twenty-one days. At each feeding session, one cubic decimeter of substrate was harvested from the production ponds and the live Chironomidae were collected with a 350-micrometer sieve. A control group received Coppens, a commercial imported feed. Growth and survival were monitored through control fishing every three days, with daily counts of mortalities and standard zootechnical calculations including daily weight gain, specific growth rate, survival rate, and a production index.

The survival outcomes were remarkable in their consistency. Fry fed Chironomidae from cow dung survived at 94 percent, rabbit droppings at 92 percent, poultry droppings at 95 percent, and pig dung at 95 percent, statistically indistinguishable from the 95 percent survival of the Coppens-fed control group. Final mean weights ranged from about 10.06 to 10.29 milligrams across all live-feed treatments, with the commercial feed group reaching 12.65 milligrams. The commercial diet did produce the highest daily weight gain and specific growth rate, with significant differences among treatments, and the authors attribute this edge to the superior protein content of the formulated feed. Nevertheless, specific growth rates in the live-feed groups, between roughly 25.50 and 26.90, exceeded those reported in comparable earlier studies, which the researchers link to the sheer abundance of Chironomidae available to the fry.

The implications extend well beyond the laboratory. The authors argue that Chironomidae produced from rabbit and poultry droppings, with protein contents between 22 and 26 percent plus their complement of fat- and water-soluble vitamins, can substitute for imported feed at the first feeding stage of catfish fry. This matters because the vitamins measured in the larvae fall within ranges previously associated with healthy growth in species such as grass carp, and vitamins A, D, E, and the B complex act as metabolic catalysts that support growth, immune function, and ultimately human health in consumers. For rural producers in Guinea and across West Africa, the practical message is that the raw materials for high-quality fry feed, essentially livestock manure and shallow ponds, are already on the farm, eliminating dependence on foreign currency, import logistics, and unpredictable supply chains that currently constrain the sector.

The study also carries broader ecological and economic resonance. By coupling organic fertilization with the natural productivity of pond ecosystems, the approach mirrors traditional aquaculture principles while adding modern analytical rigor: precise dosing, mono-specific larval culture, and full bromatological characterization. The researchers caution that protein values in their larvae were lower than those reported in some prior work, likely due to differences in culture media and larval age, and that the commercial feed retains an advantage in absolute growth rates. Yet the near-identical survival between live-feed and control groups addresses the most vulnerable stage of the production cycle, where losses are typically greatest. As fish demand continues to climb and wild fisheries face mounting pressure, low-tech innovations like manure-fertilized bloodworm ponds may prove that the future of sustainable aquaculture lies not only in high-tech feed mills but also in the small, wriggling insects that fish have been eating all along.

Subject of Research: Organic fertilizer-based production of Chironomidae larvae as live feed for Clarias gariepinus fry aquaculture

Article Title: Bromatological value of Chironomidae produced from organic fertilizers and their effects on the growth of Clarias gariepinus fry in the Guinean forest region

Article References: Adande, R., Djidohokpin, G., Djissou, A., Bilivogui, P., & Jean-Claude, M. (2025). Bromatological value of Chironomidae produced from organic fertilizers and their effects on the growth of Clarias gariepinus fry in the Guinean forest region. Blue Biotechnology, 2(1), Article 14. https://doi.org/10.1186/s44315-025-00024-y

Image Credits: AI Generated

DOI: 10.1186/s44315-025-00024-y

Keywords: aquaculture, Chironomidae, bloodworms, Clarias gariepinus, organic fertilizers, fish fry, live feed, Guinea, protein content, vitamins, sustainable fish farming, benthic macroinvertebrates