Sperm cryopreservation of sex-reversed rainbow trout (Oncorhynchus mykiss):: parameters that affect its ability for freezing

Sex control profits the aquaculture industry allowing the obtaining of "all female" rainbow trout populations. Female production is highly profitable since they become sexually mature 1 year later than males, reaching their marketable size before maturation. Sex-reversed rainbow trouts have similar external morphology to normal males but lack sperm ducts, meaning that the animals must be sacrificed to obtain the milt. The peculiarities of the sperm, obtained directly from the testicle, make necessary the development of a specific cryopreservation protocol. In this study, several factors that could affect the freezability of these spermatozoa have been studied: the season of sperm extraction, the method of sperm extraction, and the activation with motility stimulators have been considered. Our results showed that seasonality clearly affects the success of the cryopreservation process, which should always be carried out with sperm obtained in winter season, the natural breeding period. The development of a clean sperm extraction method improved significantly the fertility rates obtained with cryopreserved sperm. The addition of methylxanthines as motility stimulators usually increased motility and fertility rates, but they did not provide significant improvements. (C) 2003 Elsevier Science B.V. All rights reserved.