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Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/20/2012 Publication Date: 5/15/2012 Citation: Weber, G.M., Hostuttler, M.A. 2012. Factors affecting the first cleavage interval and effects of parental generation on tetraploid production in rainbow trout (Oncorhynchus mykiss). Aquaculture. 344-349:231-238. Interpretive Summary: Tetraploid induction causes fish to have 4 sets of chromosomes as opposed to the usual 2 sets of chromosomes. The value of tetraploid induction is the ability to cross tetraploid fish with normal diploid fish to produce 100% triploid fish (3 sets) which are sterile. Triploid fish have more efficient growth and are important to many small rural aquaculture businesses that supply fish to stocking and fee fishing operations where only sterile fish can be used due to environmental considerations. A significant impediment to reliable and efficient tetraploid induction has been the apparent variation in time requirements for cell division among individual batches of eggs. Determining this time requirement is a very labor intensive process which must be conducted for each fish providing eggs. We determined that controlling for egg age reduces the variation in this trait to the point where a few fish can be used to represent an entire population of fish, for the entire spawning season, if the fish are of the same strain and maintained under the same environmental conditions. Furthermore, we observed that 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 about 10 fold for second generation tetraploid females compared with first generation tetraploid females. All progeny of tetraploid by tetraploid crosses were determined to be tetraploids. In summary, attention to egg age and use of second generation female tetraploids allows efficient production of a tetraploid rainbow trout broodstock and tetraploid-derived triploids. Technical Abstract: 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 ageing is taken into account. Ageing 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 ageing and use of second generation female tetraploids allows efficient production of a tetraploid rainbow trout broodstock. |
