Changes in Sex Steroids, Growth Hormone, and Insulin-Like Growth Factor-I during Ovarian Development in Rainbow Trout Cultured in a Water Recirculating System with Continuous Light

Female Rainbow Trout Oncorhynchus mykiss were cultured within a freshwater recirculating aquaculture system under 24-h constant lighting in 13 degrees C water and fed every 6 h to near satiation. An opaque roof allowed surface light intensity to vary be-tween <200 and about 1,500 lx. During months 14-26 posthatch we examined changes in plasma concentrations of testosterone (T), estradiol-17 beta (E2), the maturation inducing steroid (MIS) 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17,20 beta P), growth hormone (GH), and insulin-like growth factor-I (IGF-I). Oocyte diameter was variable at the start of the study, most averaging <1 mm; diameter increased to above 3.2 mm in the final 2 months, with migrating germinal vesicles indicating they were postvitellogenic. Some ovaries exhibited atresia, and no fish ovulated, suggesting some reproductive dysfunction. Testosterone and E2 began increasing between months 16 and 18, and although T continued to increase throughout the study, E2 changed little after month 20. The MIS 17,20 beta P, remained near or below detection. Plasma GH remained relatively unchanged although values trended slightly higher during the final 4 months, GH being significantly greater at months 22, 24 and 26 than at month 16. Plasma IGF-I was higher at the first time point, month 14 posthatch than at months 20, 24, 25, and 26. In summary, gradual changes in growth and fillet quality attributes during gonadal development were accompanied by gradual changes in hormone levels, but no clear changes in hormones were associated with rapid changes in product quality traits observed around months 24-26.