Protocols for more effective induction of tetraploid rainbow trout

Authors: Hershberger, William; Hostuttler, Mark

Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2006
Publication Date: 10/1/2007
Citation: Hershberger, W.K., Hostuttler, M.A. 2007. Protocols for more effective induction of tetraploid rainbow trout. North American Journal of Aquaculture. 69:367-372.

Interpretive Summary: There is an increasing demand for triploid rainbow trout, that is, those with three sets of chromosomes for aquaculture production. Since triploid rainbow trout are sterile, they have two major production benefits: (1) losses due to early maturation are largely removed and (2) problems with escapement and reproductive interaction with natural populations are eliminated. Consistent 100% production of triploids can be realized by crossing fish with four sets of chromosomes (tetraploids) with diploids (those with two sets of chromosomes) without fish used for production being subjected to the severe treatment otherwise needed to create triploids. The research reported in this manuscript develops a treatment protocol that will yield more consistent induction of tetraploids in different genetic groups of rainbow trout. The results yielded a tetraploid induction protocol in which the treatment timing is adjusted based on the embryonic development rate and, thus, works with different genetic groups of fish. This research provided the initial steps in the creation of genetically diverse tetraploid rainbow trout lines that can be selected and crossed with diploids to yield sterile triploids with improved production traits for the aquaculture industry.

Technical Abstract: Practical use of tetraploids in rainbow trout (Oncorhynchus mykiss) culture to make triploid production fish depends on (1) the effectiveness of the induction process and (2) the ability of these fish 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. Small aliquots of eggs (~500) from individual females were immediately fertilized and evaluated for time to first cleavage. The remainder of the eggs were stored at 4'C for <24 hrs and subjected to varying hydrostatic pressures at different initiation times and durations of treatment, based on time to first cleavage. The most successful protocol involved treatment at 9,000 psi for 8 min starting at 62-65% of the time to first cleavage for two populations while the results for the third population were less clear and need further investigation. Observed population-level changes in the time to first cleavage over one generation of culture in our facilities reinforced the desirability of using protocols that varied with the time to first cleavage. With the variation noted in time to first cleavage and the lack of information on its control, we recommend that treatment initiation be based on first cleavage interval (FCI) analysis of a sample of eggs from each female used for induction of tetraploidy. 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.