Protocols for More Effective Induction of Tetraploid Rainbow Trout

Abstract Practical use of tetraploids in culture of rainbow trout Oncorhynchus mykiss to make triploid production fish depends on (1) the effectiveness of the induction process and (2) the ability of tetraploids to reproduce and yield viable offspring. Investigations were undertaken to develop a protocol for the induction of tetraploidy to compensate for differences in time to first cleavage (i.e., first cleavage interval [FCI]). Small aliquots of eggs (∼500) from individual females were immediately fertilized and evaluated for FCI. The remaining eggs were stored at 4°C for less than 24 h and were subjected to varying hydrostatic pressures at different initiation times and durations of treatment based on FCI. The most successful protocol involved treatment at 9,000 lb/in 2 (633 kg/cm 2 ) for 8 min starting at 62–65% of the FCI for two strains, while the results for the third strain were less clear and need further investigation. Observed population‐level changes FCI over one generation of culture in our facilities reinforced the desirability of using protocols that varied with FCI. With the variation noted in FCI and the lack of information on its control, we recommend that treatment initiation be based on FCI analysis of a sample of eggs from each female used for tetraploidy induction. Although more research is needed to optimize the yield from this approach to triploid production, there is the potential for the selection of the best tetraploid lines to predictably generate genetically improved triploid rainbow trout for aquaculture.