A Study on the Production Possibility of All-Female Triploid Rainbow Trout (Oncorhynchus mykiss)

In order to reduce the adverse effects of sexual maturation on growth and survival of rainbow trout, production possibility of all-female triploid was investigated by means of early heat shock on eggs fertilized by masculinized male’s sperm. Fish ploidy level was determined by erythrocyte size measurement and confirmed by gill nucleolus (NORs) counting as well as chromosome number. Sexual ratios and gonad development were determined by histological studies. Final results showed that progenies produced by mating sex-reversed (masculinized) males and normal females were totally female (100 %). Also, applying early heat shocks (26.5° C lasting 20 min, 20 min after egg fertilization) induced about 80 % triploidy in fishes. All-female triploid, all-female diploid and mixed-sex diploid fishes did not show any significant difference in incubation stages (eyed-stage egg rate, hatching, survival from hatching to active feeding), (P>0.05). Eyed-stage eggs rate, and hatching rate of eyed eggs in mixed-sex triploids were significantly lower than in other treatments (P<0.05). Testes development in diploid males was similar to that of triploid and was in early stages of spermatogenesis in 8 month old fish. Also, diploid ovaries were packed with oocytes at previtellogenic or perinucleolus stages. Although they showed distinct lamellar structure of an ovary, triploid ovaries contained no oocytes