Sex reversal of female rainbow trout by immersion in 17alpha-methyltestosterone

Authors: Weber, Gregory - Greg; Leeds, Timothy - Tim

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/23/2020
Publication Date: 5/25/2020
Citation: Weber, G.M., Leeds, T.D. 2020. Sex reversal of female rainbow trout by immersion in 17alpha-methyltestosterone. Aquaculture. 528:735535. https://doi.org/10.1016/j.aquaculture.2020.735535.
DOI: https://doi.org/10.1016/j.aquaculture.2020.735535

Interpretive Summary: The rainbow trout industry raises all-female rainbow trout. This is accomplished by treating females with a steroid during the early life stage to produce neomales that develop testes instead of ovaries. The standard industry practice is to feed the steroid to the fish for the first 60 days of feeding. The use of sperm from these neomales to fertilize eggs results in all-female offspring. This study describes an alternative immersion-based method to administer the steroid to young females. The immersion method was found to be equally effective at converting females to neomales compared to the feeding method. Additional benefits of the immersion method include easy and effective capture of unused steroid before release to the environment, and a greater ability to collect sperm from neomales non-lethally. The immersion method is better for the environment, better for the fish, and easier to execute by the farmer.

Technical Abstract: The use of oral administration of 17alpha-methyltestosterone (17MT) at 3 mg 17MT/kg of feed for 60 days following the onset of feeding to sex reverse female rainbow trout (Oncorhynchus mykiss) to produce XX males is well established. The treatment has shown to consistently result in nearly 100% of the treated animals being males. A primary drawback to this protocol is a high proportion of males are non-functional and therefore the males must be euthanized to harvest sperm from the testes. A second drawback to the protocol is the difficulty in preventing the steroid from reaching the environment when used as a feed additive. A technique for using immersion to administer 17MT for sex reversal was developed to address these issues. Immersion of female rainbow trout in 17MT at 400 ug/L for 2 h at one week post hatching, and weekly for five weeks starting at the onset of first feeding, for a total of seven immersions, resulted in nearly 100% sex reversal to male and about half the males being functional. The technique should increase efficiency of hatchery operations by allowing greater flexibility inherent in functional males, reduce the accidental harvesting of immature males, and simplify the capture of the steroid before reaching the environment.