Husbandry and Dietary Effects on Sturgeon (Acipenser transmontanus) Farmed for Caviar
A study was conducted at two sturgeon farms to test the hypotheses that husbandry and diets with different protein and lipid content affect the body weight, condition factor, caviar yield, egg texture and stage of development (egg size and germinal vesicle migration) at harvest and that vernalization affects the fish weight, condition factor, the concentrations of plasma sex steroids (testosterone, T and estradiol- 17ß, E2), and the incidence of the ovarian follicular atresia. Ninety-two individually marked females, originated from the same brood fish were fed two different diets for 6 months on each farm, followed by a 5 month vernalization at a communal coldwater facility, where the dietary treatments continued. Fish were sampled, before and after vernalization, for length, weight, plasma T and E2, and for caviar yield, egg diameter, polarization index (PI), and egg texture at the roe harvest. A two-way analysis of variance (ANOVA) did not reveal significant effects of farm, diet and their interaction on body weight, condition factor, caviar yield, egg texture and stage of development at harvest (P > 0.05). A mixed model with repeated measure revealed a significant decrease of fish weight, condition factor, and plasma T concentration during vernalization (P < 0.0001), as well as an effect of farm on plasma T concentration (P < 0.0001) and an interactive effect of farm ? sampling time (P = 0.0086) on plasma E2 concentration. Fishes maintained normal ovarian follicles and the plasma E2 concentrations during vernalization period. Histological examination revealed ovarian follicular atresia in only one female at harvest.