Comparison of Hatchery Performance, Agonistic Behavior, and Poststocking Survival between Diploid and Triploid Rainbow Trout of Three Different Utah Strains

The hatchery performance (growth, feed conversion, and survival) of rainbow trout Oncorhynchus mykiss was compared between diploid and triploid fish from three Utah strains: Fish Lake‐DeSmet (FD), Sand Creek (SC), and Ten Sleep (TS). For FD, specific growth rates were slightly higher for triploids (2.79%/d) than for diploids (2.60%/d), but final mean weight at 108 d did not significantly differ. For SC and TS, there were no significant differences in final mean weight or specific growth rates after 138 or 122 d, respectively. Feed conversion ratios and fish mortality in the raceways did not differ significantly between diploids and triploids, except for SC for which mortality rates were slightly higher for triploids (4.0%) than diploids (2.1%). Possible differences in agonistic behavior between diploids and triploids were assessed by video observation of size‐matched pairs (diploid‐diploid, diploid‐triploid, or triploid‐triploid). There were no significant differences between diploid and triploid fish of any strain in the number of chases or counterattacks. To determine whether there were any differences in susceptibility to stocking and handling stressors, each strain was transported at high density for 4 h, then stocked into (1) tanks with ambient hatchery well water (control), (2) tanks with either high pH and high temperature (FD) or high temperature (TS and SC), or (3) the tail end of the raceway from which it came. There were no significant differences in mortality after 96 h between diploid and triploid fish for any of the three strains for any of the treatments. Poststocking survival of FD in a small, spring‐fed lake was assessed by gill netting in the spring after fall stocking. No significant difference in overwinter survival was noted between diploid and triploid FD. Overall, the data indicate that triploid SC, FD, and TS rainbow trout perform equally well in the hatchery as diploid fish.