Chronic effects of dietary selenium on juvenile Sacramento splittail (Pogonichthys macrolepidotus)

The chronic effects of dietary selenium (Se) exposure in juvenile Sacramento splittail (Pogonichthys macrolepidotus) were investigated in the laboratory. A total of 960 (40 fish per tank, 3 tanks per diet) 7-month-old juvenile splittail were fed one of eight Purified-Casein diets supplemented with selenized yeast for 9 months in a flow-through system. These diets contained the following: 0.4 (control), 0.7, 1.4, 2.7, 6.6, 12.6, 26.0, and 57.6 mg of Se kg^-1 dry weight. Survival, Se tissue concentration, growth, gross morphology, and liver histopathology were assessed at 5-and 9-month of exposure. Mortalities occurred only in the two highest Se treatments and were accounted for 8.3 and 18.3% at 5-month and 10.0 and 34.3% at 9-month, respectively. Liver and muscle Se concentration were significantly correlated with dietary Se concentration. Fish exposed to 0.4-12.6 mg of Se kg^-1 diets had reached equilibrium in liver Se concentration by 5 month. Splittail fed diets at concentrations ≥26.0 mg of Se kg^-1 had not reached equilibrium in liver, and muscle Se concentrations and grew significantly slower (p < 0.05) at 5- and 9-month exposure. Se-induced deformities were observed in fish fed ≥2.7 mg of Se kg^-1 diets at 5-month and in fish fed ≥0.7 mg of Se kg^-1 diets at 9-month. Fish fed 26.0 and 57.6 mg of Se kg ^-1 diets had higher liver lesion scores at 5-month while fish fed 6.6 and 57.6 mg of Se kg^-1 diet had higher liver lesion scores at 9-month. Results indicate that survivals, growth, changes of tissue Se concentrations, and histopathology of juvenile splittail were dose-dependent, but their response thresholds to dietary Se concentrations differed and depended on treatment concentrations and duration of exposure. Chronic exposure to 6.6 mg of Se kg^-1 diet induced deleterious health effects that can potentially impact survival of juvenile splittail.