The economic logic is straightforward. In many farmed species, sex determines how fast an animal grows and how much it is worth at harvest. Male Nile tilapia grow up to 40 percent larger than females, which is why all-male tilapia populations dominate commercial production. Male yellow catfish and giant freshwater prawns also outgrow their female counterparts, while in half-smooth tongue sole the relationship is reversed, with females reaching four times the size of males. Monosex culture exploits these differences by preventing premature maturation, eliminating uncontrolled breeding in grow-out ponds, reducing size variation, and improving feed conversion. Sterility offers a complementary benefit: energy that would otherwise be spent on gonads and spawning is redirected into somatic growth, and escaped fish cannot breed with wild relatives, protecting biodiversity from genetic introgression.

Conventional methods have delivered these advantages for decades, but each carries trade-offs. Hormonal sex reversal, typically using 17α-methyltestosterone or estradiol-17β administered through treated feed or immersion during the labile window of sex differentiation, is effective but raises concerns about hormone residues, worker safety, and consumer perception. Chromosome-set manipulation, including gynogenesis and androgenesis, can generate single-sex or clonal lines but demands specialized expertise. Triploidy, induced by thermal or pressure shocks to render Atlantic salmon, rainbow trout, and grass carp functionally sterile, remains the workhorse of reproductive containment. Yet triploid fish often pay a welfare price: studies have linked the extra chromosome set to cataracts, skeletal deformities, reduced aerobic capacity, lower survival, and growth that can fall to 75 to 90 percent of diploid levels. YY supermale technology in tilapia, in which sex-reversed females are crossed to produce males carrying two Y chromosomes, has proven commercially successful but depends on long breeding cycles and, in many strains, hormone treatment.

Genome editing changes the calculus. CRISPR/Cas systems use Cas proteins as molecular scissors guided by RNA to cut DNA at chosen sequences, and newer variants expand the toolkit considerably. Cas12a makes staggered cuts, Cas13 targets RNA, and catalytically dead Cas9 can regulate genes without cutting at all. Base editors convert single nucleotides without double-strand breaks, and prime editing enables versatile small modifications with fewer unintended insertions and deletions. In fish, these tools can target the genes that govern sex determination and germ cell survival. Disrupting male pathway genes such as dmrt1, amh, amhr2, gsdf, or the crustacean androgenic gland gene iag can push development toward all-female populations, while knocking out female pathway genes such as cyp19a1a, foxl2, or cyp17a1 can masculinize genetic females and yield all-male cohorts. Targeting dnd, a gene essential for primordial germ cell survival, produces fish that develop normally but carry no germ cells at all.

The proof-of-concept results are striking. In common carp, CRISPR knockout of cyp17a1 converted XX females into neomales with 60 to 85 percent penetrance, and all-female cohorts produced from these neomales grew 10 to 20 percent faster than mixed-sex controls. In Nile tilapia, dmrt1 knockout converted 70 to 100 percent of XY genetic males into neofemales, which were then used to generate YY supermales with 18 to 30 percent efficiency; their all-male offspring outweighed mixed-sex siblings by 10 to 30 percent. In the ridgetail white prawn, iag knockout caused male-to-neo-female sex reversal, although larval survival dropped by 20 to 50 percent, underscoring that crustacean editing remains experimental. Crucially, gene editing serves mainly to create founder broodstock; large-scale monosex production then proceeds through ordinary breeding, meaning the fish that reach dinner plates can be free of foreign DNA, a distinction that matters for regulators classifying such edits as SDN-1-type changes rather than transgenic GMOs.

Sterility engineering follows a similar logic but pairs editing with germ cell transplantation. Knocking out dnd ablates endogenous germ cells while leaving the somatic gonad intact, creating sterile recipients that act as living bioreactors. Donor spermatogonia or oogonia, harvested from elite or edited lines and optionally cryopreserved, are transplanted into these recipients, where they colonize the gonads and produce eggs or sperm carrying exclusively the donor genome. In rainbow trout, homozygous dnd knockouts supported donor germ cell colonization rates of 30 to 70 percent, with fertility restored in more than 60 to 90 percent of colonized recipients and donor-derived gamete production reaching 80 to 100 percent of wild-type levels, while the edited recipients themselves grew within 5 percent of normal fish. Germ cell-less mackerel hybrids have produced viable donor-derived offspring, and in Atlantic salmon, gonadal cell suspensions transplanted into triploid hatchlings generated functional donor-derived ovaries and sperm. Edited sterile salmon showed growth, stress response, and sea lice resistance equivalent to fertile diploids, outperforming triploids, which suffer higher deformity rates of 10 to 40 percent and greater environmental sensitivity.

Despite these advances, no genome-edited monosex or sterile fish line has yet achieved routine commercial production, and the review identifies five interlocking bottlenecks. First, the master sex-determining gene remains unknown in more than 80 percent of farmed fish species, making target selection speculative. Second, editing efficiency varies enormously, from under 1 percent to as much as 90 percent depending on species, target, and delivery method, with F0 mosaicism frequently exceeding 40 to 70 percent and forcing multi-generational breeding to stabilize edits, a slow process in salmon that take three to four years per generation. Third, delivery is a throughput bottleneck: manual embryo microinjection handles roughly 3,000 eggs per technician per day with post-injection survival often below 70 percent, inadequate for high-fecundity species like tilapia that produce 1,000 to 2,000 eggs per female. Fourth, germ cell transplantation success is highly species-dependent, exceeding 70 percent colonization in rainbow trout but falling below 20 percent in many marine teleosts. Fifth, regulation is fragmented: the European Union treats edited fish as GMOs regardless of whether foreign DNA is present, the United States applies a risk-based FDA framework for heritable genomic alterations, and China has begun distinguishing gene-edited plants from conventional GMOs while rules for edited animals remain unsettled.

The authors argue that overcoming these barriers requires convergence across disciplines rather than incremental biology. Machine learning models trained on comparative genomics, chromatin accessibility data, and single-cell gonad atlases could predict sex and fertility genes in non-model species, although such multi-omics resources remain scarce for most farmed taxa. Robotic microinjection arms, microfluidic embryo arrays, and electroporation of CRISPR ribonucleoproteins could scale editing beyond 50,000 embryos per day. AI-based imaging and behavior tracking could identify monosex or sterile candidates non-invasively, reducing culling. Global cryobanks of spermatogonia and oogonia paired with cloud-based genetic metadata could enable germplasm-on-demand, shipping elite donor cells to hatcheries with locally adapted sterile surrogates. On the policy side, the review advocates product-based regulation that judges the final trait, such as sterility or monosex status, rather than the editing process, citing Argentina, Brazil, and Japan as pioneers of this approach. Environmental validation is also essential, since temperature, hypoxia, and stocking density can shift sex differentiation and alter the performance of both triploid and edited stocks.

The review also confronts the ethical dimensions head-on. Off-target mutations, mosaicism, and developmental abnormalities can occur during protocol optimization, and heritable germline modifications raise questions about long-term consequences and human intervention in reproduction. Induced sterility itself has welfare implications that deserve study, and public scepticism toward gene-edited seafood persists even where the environmental credentials exceed those of hormone-based methods. The authors call for rigorous welfare assessment, transparent labelling, third-party environmental risk evaluation, and farmer and consumer co-design of deployment models. Their proposed two-tier platform separates genetic innovation, confined to breeding centers where stable edited lines are created and validated, from large-scale gamete production at hatcheries using sterile surrogate broodstock, decoupling genome editing from commercial seed supply while maintaining reproductive containment. The ultimate measure of success, they conclude, will not be editing efficiency or colonization rates but whether these tools deliver safe, affordable, environmentally sound seafood without compromising biodiversity or equity. If biological precision can be aligned with social responsibility, genome-edited monosex and sterile fish could become foundational to a climate-adaptive, circular aquaculture economy, much as hybrid seed systems transformed terrestrial agriculture.

Subject of Research: CRISPR-based genome editing and germ cell transplantation for producing monosex and sterile fish in sustainable aquaculture

Article Title: Engineering monosex and sterile fish for food production: from conventional methods to CRISPR-based precision

Article References: Min, Y., Sun, F., Wong, J., Lee, M., & Yue, G. H. (2026). Engineering monosex and sterile fish for food production: from conventional methods to CRISPR-based precision. Advanced Biotechnology, 4(3), Article 30. https://doi.org/10.1007/s44307-026-00128-5

Image Credits: AI Generated

DOI: 10.1007/s44307-026-00128-5

Keywords: aquaculture, CRISPR, genome editing, monosex fish, sterile fish, germ cell transplantation, surrogate broodstock, triploidy, Nile tilapia, Atlantic salmon, reproductive biocontainment, sustainable seafood