Factors affecting the first cleavage interval and effects of parental generation on tetraploid production in rainbow trout (Oncorhynchus mykiss)

Tetraploidy is induced in rainbow trout by applying a pressure shock at a specific time point between insemination and first cleavage, or the first cleavage interval (FCI). Previous studies suggested that variation in the FCI among individuals and populations of fish prevents the identification of a single time point that can be used for all trout. In this study we confirmed the optimal time to apply pressure is 65 +/- 5% of the FCI. In addition, we found that variation in FCI of fish from a common environment can be within limits that allow a single time point to be established for that group of fish, if ova post ovulatory aging is taken into account. Aging of ova, either in vivo or in vitro, increased FCI to a degree that is a concern for tetraploid induction. The FCI was about 12 min longer at 7 days post ovulation, and 30 min at 10-14 days, than at 1 day. The FCI for a group of fish was consistent throughout the spawning season. Survival to hatching and frequency of spinal abnormalities were similar for progeny of first and second generation tetraploid males, but survival was doubled and abnormalities reduced by approximately 90% in second generation tetraploid females compared with first generation females. All progeny of tetraploid by tetraploid crosses were determined to be tetraploids based on flow cytometry of embryonic cells. In summary, attention to ova aging and use of second generation female tetraploids allows efficient production of a tetraploid rainbow trout broodstock. Published by Elsevier B.V.