Effects of dietary estradiol-17β in juvenile shortnose sturgeon, Acipenser brevirostrum, Lesueur

Shortnose sturgeon, Acipenser brevirostrum, were fed estradiol-17β (E2) in commercial salmon feed in two separate experiments, with the aim of creating all-female populations for aquaculture. In the first experiment, 5-month-old fish were fed 0 (control), 10, 50 and 100 mg E2/kg feed during a 9-month trial starting in September. This experiment was confounded by copper contamination of the heated water source that appeared to cause E2-dose-dependent mortality. As a result, a second, parallel experiment was conducted on the same year class of fish starting at age 7 months in November, but with hormone dosage reduced to 0, 10, 25 and 50 mg E2/kg feed in a 7-month trial. In both experiments, control and 10 mg E2/kg groups remained active and fed well, but the other fish were less active and fed less as E2 dosage increased. Histological observations indicated that anatomical differentiation of the ovaries had begun in 3 of 5 individuals examined at the start of Experiment 2. In January, sub-samples of 6 fish from each group showed that E2-treated fish had mottled livers, swollen kidneys and reduced gonad size. The number of hepatocytes and their staining characteristics were similar in both the control and 10 mg E2/kg groups. At 25 mg E2/kg and higher, the number of hepatocytes and the presence and quantity of yolk protein increased with the E2 dosage. At final sampling in May, all of the treatment groups showed some individuals with these pathologies evident macroscopically, and their frequency and severity increased with E2 dosage such that all individuals of the 100 mg E2/kg group were affected. In general, fish grew better and had lower mortality in Experiment 2 (8.5%, as compared to 15.2% for Experiment 1) during the period of E2 treatment. Final sampling revealed that all treated fish were apparently feminized in both experiments, based on anatomical differentiation of the gonads. Control groups, on the other hand, were 65 and 58% female in Experiments 1 and 2, respectively.