Gonadal regeneration in masculinized female or steroid-treated rainbow trout (Oncorhynchus mykiss)

In salmonids, the development of an indifferent gonad into a testis or an o vary is normally determined chromosomally but can be reversed or changed by the administration of exogenous steroids during specific times in embryoni c development. Because the gonads of sexually mature rainbow trout (RBT) ar e capable of regeneration following surgical removal and since regeneration of some tissue involves dedifferentiation, the objective of this experimen t was to determine if the phenotypic sex of RBT gonads could be reversed du ring the regenerative process. In experiment 1, male RBT were surgically go nadectomized (Gx) or left intact and subsequently treated with estradiol-17 beta, a steroid that feminizes male RBT embryos. All Gx males regenerated testicular tissue regardless of treatment. Likewise, the gonads of sham-ope rated, intact fish treated with exogenous estrogen showed no evidence of se x-reversal. In experiment 2, testes from masculinized females (XX genotype; male phenotype) were surgically removed. In all cases, only testicular tis sue was regenerated in the masculinized females. Taken together, these resu lts are consistent with the conclusion that gonads of salmonid fishes are n ot susceptible to sex-reversing stimuli during the regenerative process and that gonadal regeneration in salmonids is a result of cellular proliferati on of the remaining gonadal remnant. (C) 2001 Wiley-Liss, Inc.