Production of all-female rainbow trout stocks for aquaculture requires the use of the steroid 17a-methyltestosterone, a regulated compound. This project examines the genetic mechanisms behind the occurrence of rare male phenotypes in all-female populations of rainbow trout for future use in breeding programs without the use of this steroid. OBJECTIVES: The proposed SBIR project seeks to develop an alternative approach to the use of hormone treatment (17a-methyltestosterone) of broodstock for the production of all-female rainbow trout. In the course of normal spawning of large numbers of rainbow trout, Troutlodge personnel have identified rare occurrences of males in populations of XX female stocks. Previous studies using common carp in the Netherlands and rainbow trout in France have identified similar rare male individuals and determined that they are the result of homozygosity for a recessive autosomal sex-determining allele that overrides the normal XX-XY sex determination mechanism. This project will test for a similar phenomenon in Troutlodge stocks of rainbow trout, and utilize these alleles to establish male lines of XX individuals without the use of testosterone analogs. APPROACH: Rare males found in all-female populations of rainbow trout will be tested for (1) their ability to produce all female progeny in crosses with normal females, and (2) their ability to produce significant numbers of male progeny when their sperm is used for androgenesis (all-paternal inheritance). If both objectives are successful, it will indicate that autosomal sex reversal is likely and lead directly to Phase II research
