Early growth and survival of heat-shocked and tetraploid-derived triploid rainbow trout ( Oncorhynchus mykiss)

To assess the importance of genetic composition and induced polyploidy, triploidy was induced in an interstrain hybrid of rainbow trout via two distinct methodologies: (1) the thermally induced retention of the second polar-body, and (2) the crossing of tetraploid and diploid individuals. Groups were reared separately in replicate tanks up to 120 days post-ponding. The triploid group derived from tetraploid male×diploid female “interploid” crosses experienced a low level of fertilization success, 55.9% of controls, relative to the heat-shocked triploid group, 94% of controls. High levels of aborted embryos, 14.7%, were found in the egg lots subjected to the heat-shock treatment, in comparison to 0.5% in controls and 0.4% in the interploid group. The weight of heat-shocked triploids after ponding was significantly lower than their controls for the first 63 days, by as much as 24.5%. The heat-treated triploids subsequently showed a rapid increase in weight from day 63–82 resulting in no significant difference between them and their controls from 82–118 days post-ponding. Although the interploid triploids were initially significantly larger than their controls, they were significantly smaller than controls from day 82–102. At the conclusion of the study, all of the groups, triploid and diploid, were similar ( P > 0.05) in weight. In general, the interploid method of induction produced more vital fry, and under more rigorous commercial rearing conditions these fish may be superior to heat-treated triploids.