Tilapia is a cornerstone of Philippine aquaculture, ranking third in production volume among cultured fishery species, with Nile tilapia the dominant species. But Nile tilapia is a freshwater fish, and limited freshwater availability constrains expansion. To overcome this, UPV crossbred saline-tolerant O. spilurus males with fast-growing O. niloticus females, producing the UPV SpiN hybrid, which inherits salinity tolerance from one parent and rapid growth from the other. The hybrid is now cultured at the UPV multi-species hatchery for research and potential commercial production, particularly in coastal areas affected by seawater intrusion and climate change.

Monosex culture is standard practice in tilapia farming because uncontrolled reproduction leads to overstocking, disease, competition, and growth regression. All-male production is usually preferred commercially, since males grow faster and larger and command higher market prices, and sex reversal with androgens is widely used for that purpose. But broodstock operations need females: fry quality and quantity depend heavily on maternal size, gonadosomatic index, and fecundity, and breeding schemes typically use two to four, or even up to seven, females per male. A reliable supply of female breeders is therefore essential, and estrogen hormones such as 17β-estradiol (E2), chosen for its natural origin and ease of metabolism and excretion, can generate it.

The team tested two administration methods. In the first, swim-up fry after yolk-sac absorption received E2 through dietary supplementation at 0, 50, 100, or 200 mg per kg of feed for 28 days, with hormone dissolved in ethanol, sprayed onto commercial fry feed, and evaporated in a fume hood for at least 72 hours before use. In the second, larvae still carrying yolk sacs were immersed in E2 solutions at 0, 50, 100, 200, or 400 µg per liter for five days, until the yolk sac was fully absorbed. After treatment, all fish were reared without hormones in freshwater, then gradually acclimated to 10–20 ppt salinity until they reached 100–150 g for sex sorting.

Survival was remarkably high in both batches. Dietary supplementation produced survival rates of 99.17 to 100 percent, with no significant differences among treatments, showing that even the highest E2 dose did not harm the fry. Immersion survival ranged from 85.56 to 100 percent during the five-day exposure and from 83.33 to 98.89 percent afterward, again with no significant differences. The feminization outcomes, however, diverged sharply between the two methods.

Feeding E2 dramatically shifted sex ratios. The untreated control produced only 49.44 percent phenotypic females, while all hormone-treated groups produced far more: 97.94 percent at 50 mg per kg, 97.28 percent at 100 mg per kg, and 93.97 percent at 200 mg per kg, all significantly higher than the control. Feminization efficiency, calculated as the proportion of genetically male (XY) individuals that appeared as phenotypic females, peaked at 95.24 percent with 100 mg per kg and 94.74 percent with 50 mg per kg. The highest dose of 200 mg per kg offered no additional benefit, yielding 88.71 percent, a plateau consistent with findings in other species such as O. mossambicus, O. niloticus, wels catfish, and banana shrimp, where excess hormone can even cause intersex development, morphological anomalies, or reduced survival.

Immersion, by contrast, largely failed. Although survival remained high, phenotypic female ratios in treated groups did not differ significantly from the control, and only the 100 µg per liter group showed any feminization, at a low efficiency of 16.67 percent. The authors attribute this to the short exposure duration, the early developmental stage, and physiological limitations in hormone uptake at the yolk-sac stage. Previous studies that succeeded with immersion used longer exposures, such as 15 days in catfish, or varied efficiencies depending on embryo age and exposure length, suggesting that UPV SpiN larvae need more sustained contact with the hormone than five days allows.

A key strength of the study is its molecular confirmation of sex reversal. Rather than relying solely on external anatomy, which can be ambiguous, the researchers used PCR with the Marker-5 primer set targeting the amhy sex-determining gene on linkage group 23, amplifying a 1422 bp fragment from the X chromosome and a 982 bp fragment from the Y chromosome. Phenotypic females carrying XY genotypes were classified as sex-reversed genetic males, providing robust evidence that the hormone genuinely converted males rather than merely shifting natural sex ratios. To match each DNA sample to the correct individual without costly PIT tags or dye marks, the team devised a low-cost identification system: selectively excising the first six dorsal fin spines in distinct patterns, generating up to 63 unique codes. The excised spines heal naturally within weeks, but since DNA extraction and analysis finish within days, the temporary mark is sufficient.

The practical implications extend beyond broodstock supply. Identifying and selecting sex-reversed XY females is a critical step in producing YY supermales, which can generate all-male progeny without continued hormone treatment, integrating feminization protocols with sustainable monosex culture. All-female broodstock can also increase fry output, addressing the gradual decline in tilapia supply observed in recent years. Given the hybrid’s saline tolerance, the protocol is particularly valuable for aquaculture in regions affected by seawater rise and salinity intrusion driven by climate change.

The authors caution that further work is needed before the protocol reaches commercial maturity. Comprehensive evaluations of growth and reproductive performance in sex-reversed XY females compared with normal XX females are required to ensure their suitability for long-term breeding programs in saline-affected areas. Still, the study demonstrates that a 28-day dietary treatment with 50–100 mg per kg of E2 is an effective, reliable, and survival-safe method for feminizing UPV SpiN, offering hatcheries a straightforward strategy to build all-female stocks for sustainable tilapia breeding.

Subject of Research: Hormonal feminization of the saline-tolerant UPV SpiN tilapia hybrid using 17β-estradiol

Article Title: Feminization of a saline-tolerant tilapia hybrid, UPV SpiN ( Oreochromis spilurus × O. niloticus ) ( Actinopterygii , Cichliformes , Cichlidae ) using 17β-Estradiol: Effects of dose and administration method

Article References: Dinaga, C. J. P., Genciana, A. B. N., Failaman, A. A., Fontanilla, M. A. G., Estrada, R. A., Mameloco, E. J. G., Ferriols, V. M. E. N., Traifalgar, R. F. M., & Lumayno, S. D. P. (2025). Feminization of a saline-tolerant tilapia hybrid, UPV SpiN (Oreochromis spilurus × O. niloticus) (Actinopterygii, Cichliformes, Cichlidae) using 17β-Estradiol: Effects of dose and administration method. Acta Ichthyologica et Piscatoria, 55, 227-235. https://doi.org/10.3897/aiep.55.161420

Image Credits: AI Generated

DOI: 10.3897/aiep.55.161420

Keywords: tilapia, aquaculture, 17β-estradiol, feminization, sex reversal, UPV SpiN hybrid, broodstock, PCR genotyping, saline tolerance, Philippines, monosex culture, hatchery

The research, led by Xinxin Zhang, Yangen Fan, and Jian Hou together with colleagues at Shandong Agricultural University and partner institutions in China’s Shandong Province, addresses a persistent gap in the molecular toolkit of tea science. While whole chloroplast genome sequencing can reveal detailed evolutionary relationships, the cost and technical demands of such approaches put them beyond the reach of many breeding stations, germplasm repositories, and certification laboratories, particularly in the developing regions where tea cultivation is most economically important. What has been needed, the authors argue, is a practical, routine, and affordable means of maternal lineage analysis that ordinary laboratories can adopt without specialized equipment.

To build that tool, the team began at the source: they sequenced eighteen representative tea chloroplast genomes and scoured them for insertion/deletion polymorphisms, the small stretches of DNA that have been lost or gained as different lineages diverged over evolutionary time. These InDel variations are attractive markers for several reasons. They are typically bi-allelic, which makes scoring unambiguous, and when the length differences are large enough, they produce DNA fragments of visibly distinct sizes that can be separated on a simple gel, eliminating the need for expensive capillary sequencing or fluorescent genotyping platforms.

From the genome-wide survey, the researchers developed twenty-five polymorphic markers, each showing fragment length variation of more than four base pairs, a threshold chosen to guarantee that alleles could be reliably distinguished by electrophoresis. The result is a marker panel that converts the rich information content of complete chloroplast genomes into a workflow that any competent molecular biology laboratory can execute. Because chloroplast DNA in most flowering plants, including tea, is inherited maternally, these markers act as a signature of the seed parent, allowing researchers to trace the maternal ancestry of any accession directly.

The power of the panel was demonstrated in a phylogenetic analysis of one hundred tea accessions. The tree reconstructed from the InDel markers closely matched the relationships inferred from whole chloroplast genome sequences, a finding that validates the marker set as a faithful, low-cost proxy for the far more expensive gold-standard approach. For germplasm managers who need to organize collections, identify duplicates, and understand the family structure of their material, this correspondence means they can now obtain chloroplast-level resolution without generating a single full genome sequence.

Recognizing that even twenty-five markers may be more than some applications require, the team then turned to computational optimization. Using the software Core Hunter 3, which is designed to select maximally diverse core subsets from larger marker collections, they distilled the panel down to a fifteen-marker core. A Mantel test, a statistical procedure that compares distance matrices, confirmed that the reduced set remained highly representative of the full panel, with a correlation coefficient of 0.94. In practical terms, this means that laboratories screening large numbers of samples for routine authentication can halve their genotyping costs while sacrificing almost no discriminating power.

The study’s authenticity test provides a vivid illustration of why such a tool matters. Seven seedlings, all labeled as the famous Chinese cultivar Longjing 43 but sourced from different suppliers, were fingerprinted with the marker system. Only two of the seven matched the reference fingerprint of the genuine cultivar. The remaining five did not. For a tea industry in which elite clonal cultivars command premium prices and mislabeling can propagate quietly through nurseries for years, the implications are striking: a substantial fraction of planting material sold under a prestigious name may not be what it claims to be.

Cultivar misidentification is more than a commercial nuisance. Breeding programs depend on accurate pedigree records, and when the maternal parent of a stock is wrong, decades of crossing and selection decisions can rest on false assumptions. Conservation efforts face a parallel problem: germplasm banks that cannot reliably distinguish accessions may hold redundant duplicates while missing genuinely unique diversity. By providing a maternal-lineage marker system that is both reliable and affordable, the new panel equips the tea community to audit its collections, verify nursery stock, and reconstruct the maternal history of the varieties that define regional tea cultures, from Longjing in Zhejiang to the expanding plantations of Shandong.

What sets this work apart, the authors emphasize, is that the entire workflow has been standardized and documented in a form that is transferable to other species. The logic of the approach, sequencing a small number of representative chloroplast genomes, mining the InDel variation, and filtering for length polymorphisms amenable to gel-based genotyping, does not depend on anything unique to tea. Other orphan crops, medicinal plants, and tree species that lack well-developed molecular marker resources could follow the same recipe to build their own panels, potentially closing the genetic identification gap across a wide swath of globally important plant genetic resources.

The tea plant, Camellia sinensis, is among the most economically significant non-food beverage crops on Earth, supporting millions of smallholder farmers and an industry worth tens of billions of dollars annually. As climate pressures and market demands push breeders to develop new cultivars at a faster pace, the infrastructure for verifying genetic identity becomes ever more critical. This study delivers what its authors describe as the first systematic chloroplast InDel marker panel for tea: twenty-five markers for reliable maternal genetic analysis, a fifteen-marker core subset for cost-effective large-scale authentication, and a demonstration that both can be run on equipment found in modest laboratories worldwide. For a crop whose history spans millennia and whose future depends on disciplined genetic management, the ability to read maternal lineages for the price of a gel may prove to be one of the more quietly transformative contributions to tea science in recent years.

Subject of Research: Development of a cost-effective chloroplast InDel marker panel for tea germplasm discrimination and maternal lineage tracing

Article Title: A cost-effective chloroplast InDel marker panel for tea germplasm discrimination and maternal lineage tracing

Article References: Zhang, X., Fan, Y., Hou, J., Yuan, Q., Wang, H., Wang, Z., Li, Y., Xiang, Q., Huang, Y., Lv, Y., Xu, L., He, Z., Zhang, L., & Ren, L. (2026). A cost-effective chloroplast InDel marker panel for tea germplasm discrimination and maternal lineage tracing. Plant Methods. https://doi.org/10.1186/s13007-026-01595-6

Image Credits: AI Generated

DOI: 10.1186/s13007-026-01595-6

Keywords: tea, Camellia sinensis, chloroplast, InDel markers, germplasm authentication, genetic markers, maternal lineage, molecular breeding, Longjing 43, Core Hunter, PCR genotyping, plant methods