ARS | Publication request: PRODUCING ALL FEMALE RAINBOW TROUT: DO NEOMALES AFFECT THE GROWTH OF THEIR SIBILINGS?

Submitted to: Aquaculture America Conference
Publication Type: Abstract
Publication Acceptance Date: November 30, 2005
Publication Date: February 10, 2006
Citation: Silverstein, J. 2006. Producing all female rainbow trout: do neomales affect the growth of their sibilings?. Aquaculture America Conference February 13, 2006, Las Vegas, NV.

Technical Abstract: Sex-reversal using feed mixed with androgens to masculinize rainbow trout is a common practice for perpetuating all female lines. When maintaining many families, tank space and genetic identity become difficult bookkeeping issues. One solution has been to complete sex-reversal in small tanks, and then mark and mix the treated fish (neomales) back into their full sib family tank for further rearing. Consequently, we are concerned that androgen treated, sex-reversed fish will be larger and possibly more aggressive thus affect the growth of their cohorts in the same tank. To evaluate the impact of adding neomales to full-sib groups of all females, we measured length and weight and then fin-clipped to distinguish sex reversed fish (n=20 per family) and took lengths and weights of a random sample of their full-sib counterparts (n=30) and then mixed the 20 fin-clipped neomales with 180 full-sib family members (14 family groups). We also measured length and weight of individuals from an additional 5 groups maintained at the same densities that did not receive any sex reversed animals, as controls. All tanks had 200 fish. The change in length, weight and condition factor and the coefficient of variation (CV) for length and weight of these groups was evaluated after one month of rearing. We found that at the time of mixing the neomales into their full-sib families, the neomales were significantly longer, heavier and had a higher condition factor than the rest of their families. In addition, the CV for length and weight of the neomales was greater than for the remainder of their families and for the families without neomales added. Over one month, the growth rate of families that had neomales did not differ from the growth rate of families without neomales. Neomales continued to be heavier and had a higher condition factor than their untreated cohorts, though there was no difference in length. The CV for length and weight of the neomales continued to be greater than for the remainder of their families. Comparison of the CVs for length and weight between families with and without neomales added showed no differences. In summary, the neomales themselves were longer and heavier than fish not treated with androgens, and they remained heavier as much as one month after mixing. Nevertheless, the neomales did not affect the growth of their untreated family members nor their variation in size. This study suggests that pooling sex reversed rainbow trout with their untreated cohorts (20 sex reversed fish into 180 untreated fish) will not affect growth nor the variation in length or weight of the untreated fish.