Recent advances in hormonal induction of sex-reversal in fish

Abstract

A neuroendocrine peptide can induce sex-reversal in pro-togynous labrid teleosts, similar to androgenic and antiestrogenic steroids. Culture water containing metabolites of 17a-methyltestosterone (MT), when recirculated, are more potent to induce sex-reversal than dietary supplemented MT; human estrogens present in sewage water, or other pollutants derail the normal course of sex differentiation. Steroid administration by immersion is 200-1,000 times cheaper than dietary supplementation; discrete immersion for 2-8 hours per day for 1-3 weeks after hatching induces maximal sex-reversal in salmonids like coho salmon, Oncorhynchus kisutch, while others like chinook salmon, O. tshawytscha, require dietary supplementation. Studies on uptake, disposition in the organs, and elimination of unlabeled or labeled steroids have indicated that the androgen is absorbed within one hour after intake, and selectively retained it in gall bladder, pyloric caeca and liver at higher concentrations for a longer time; however, 90-95% of the steroid is eliminated within 1-2 weeks. Estimated residual steroid of < 5 ng/g fish is too low to be a hazard to human health. Steroid delivered through water can be absorbed and retained by egg yolk of salmonids and is gradually released into the developing embryos. Temperature and autosomal gene(s) alter the process of sex differentiation in hormonally sex-reversing fish. Suboptimal treatment of steroids results in the production of hermaphroditic and intersex individuals. Hormonally sex-reversed fish also suffers from low survival and functional deficiences. The Indian scenario on the use of hormones for monosex aquaculture is described.