Comparative growth and development of diploid and triploid coho salmon, Oncorhynchus kisutch

Abstract

This paper compares growth and gonadal development of triploid and diploid coho salmon in three treatment groups. The comparisons were made in fresh and seawater from the time of smoltification at 18 months to the onset of sexual maturity at 30 months. No differences were detected in the ability of triploids to smoltify and to successfully adapt to seawater under normal conditions. Likewise, no differences were observed in growth parameters (length, body weight or condition factor). Gonadal development in both sexes was severely retarded in all triploid groups at 30 months of age. The average gonadosomatic index (GSI) of triploid males was 35.7% of diploids, but overall male gonadal development was not far enough advanced to determine if spermiation was altered in the triploids. Triploid females showed an almost complete blockage of gonadal development and oocyte maturation. The average GSI of triploid females was 11.8% that of diploid females. Vitellogenin was undetectable in triploid females, but was present in diploid females; a correlated reduction in the hepato-somatic index was observed in triploid relative to diploid females. However, we did not detect any significant differences between levels of estradiol in the plasma of triploids and diploids at this time.