Better growth in all-female diploid and triploid rainbow trout

We compared growth of all-female triploid (AFT: 87% triploid), all-female d iploid (AFD, and mixed-sex diploid (MSD) rainbow trout Oncorhynchus mykiss in a 265-d growth trial. Triploidy was induced by heat-shocking eggs to pre vent second polar body exclusion. Three AFT families, three corresponding f ull-sibling AFD families, and three MSD families that were half-siblings of the AFD and AFT families were used. Mean initial weights (SD) were 94 g (1 4), 84 g (12), and 112 g (14) for the MSDs, AFDs, and AFTs, respectively, a nd final weights (SD) were 521 g (22), 568 g (68), and 749 g (30). Growth w as linear. Growth was highest for the AFTs (2.38 g/d), lowest for the MSDs (1.58 g/d), and intermediate for the AFDs (1.78 g/d). No significant differ ences (P > 0.05) were found among treatments for survival, food conversion ratio, condition factor, liversomatic index, viceral fat, and dress-out. By day 180, however, the majority of the MSD males were sexually mature, wher eas the MSD females and the AFDs were still maturing; mean gonadosomatic in dices at day 180 were 3.1 for MSD males, 1.1 for MSD females, 1.9 for AFDs, and 0.4 for AFTs. Monosex female trout, diploids and triploids, show promi se for practical trout farming due to their faster growth and the eliminati on of males, which mature and lose flesh quality earlier. Farmers should co nsider AFT production, especially for markets using larger trout.