Production of all female triploid rainbow-trout, Oncorhynchus mykiss ( Pisces, Salmonidae). III í Growth up to first sexual maturation

Abstract

Growth and survival were compared between all-female and mixed-sex groups of diploid and triploid rainbow trout, Oncorhynchus mykiss, reared separately from first feeding up to completing the first reproductive cycIe. All-female groups were generated using sperm from genotipic females masculinized with 17âˆÂ-methyltestosterone. Triploidy was induced by a 28°C heat shocking in inseminated eggs, for 20 minutes, starting 10 minutes after egg activation. At the end of the first rearing period (12 months) the heat-shocked groups showed higher mortality than their respective diploid controls. In the second rearing period (from 12^th through 26^th month) the mortality was more severe in the diploid groups, especially among the males. Diploids, especially from the mixed-sex groups, grew faster than triploids until the first spawning season. After that, triploids, especially from all-female groups, reached higher weights than the diploids one. Externally, triploid males showed the typical secondary sex characteristics of ripe males, whereas triploid females kept the appearance of juvenile fishes. These results preclude the use of mixed-sex groups in the triploids production and support the usefulness of sterile all-female groups generated by the association of sex reversal and triploidization in trout farming oriented to production of large-sized fish.