Growth performance comparison of intercross-triploid, induced triploid, and diploid rainbow trout

•Mean body weight of 3NC fish was 28% greater than 3NP or 2N fish at 22 months of age.•Condition factor differed among ploidy types, 3NC < 2N < 3NP, at most time points.•Body weight was more highly correlated between 2N and 3NC fish, than 2N and 3NP fish.•Ploidy and family interacted to affect body weight, but effect decreased over time.•The 3NC fish exhibited much fewer vertebral compression deformities than 3NP fish.

Use of all-female triploids (3N) instead of diploids (2N) can be advantageous in rainbow trout (Oncorhynchus mykiss) aquaculture and fisheries management due to sterility and the consequent superior growth and feed conversion achieved at reproductive age. Triploid trout are currently produced by pressure or temperature shock of the zygote (induced-triploid, 3NP). An alternative procedure to create triploids that may have fewer negative effects on embryonic development and result in 100% triploids is to mate a tetraploid (4N) parent with a 2N parent (intercross-triploid, 3NC). We compared growth performance of nine sets of families each consisting of 3NP, 3NC, and 2N siblings through two years of age. The 2N and 3NC fish exhibited greater body weight than the 3NP fish throughout most of the study; however, by the end, body weight of the 3NC fish exceeded that of the 2N and 3NP fish, which were similar. Condition factor was lowest for 3NC and highest for 3NP fish throughout most of the study. Higher rates of vertebral compression in the 3NP fish affected body weight, fork length, and condition factor in this group. The correlations of body weight among families for the three ploidy types ranged from R2 below 0.03 around 8–9 months post-hatch, to above 0.5 around 18–19 month post-hatch, supporting family differences in growth response to triploidization and triploidization strategy. Nevertheless, a greater correlation between 2N and 3NC values than 2N and 3NP values, particularly at body weights above 1 kg, supports greater potential to improve 3NC growth performance compared to 3NP performance when genetic selection is based on the 2N phenotype.