Selenium depuration: residual effects of dietary selenium on Sacramento splittail (Pogonichthys macrolepidotus)

We examined the growth performance, tissue selenium (Se) concentration, and histopathology of Sacramento splittail (Pogonichthys macrolepidotus) fed a control diet (0.4 microg Se/g) for 1, 3, 7, 13, 21 wk after a 9-month dietary exposure to 0.4, 12.6, 26.0, and 57.6 microg Se/g dry diet. Splittail previously fed 57.6 microg Se/g showed a significantly (P<0.05) lower final body weight but had higher weight gain than fish fed 0.4 microg Se/g diet at the end of the 21-wk depuration study. There were no significant differences in body weight in fish previously fed diets with or less than 26.0 microg Se/g. Liver and muscle Se concentrations decreased significantly in fish previously fed 26.0 and 57.6 microg Se/g diet but did not change significantly in fish fed 12.6 or less mug Se/g diet at the end of 21 wk. Liver Se concentrations dropped to the same concentration as fish fed 0.4 microg Se/g diet after a 13-wk depuration in all treatments. Muscle Se concentrations remained significantly higher in fish previously fed 12.6 or higher microg Se/g diets when compared to fish fed control diet at the end of a 21-wk depuration. Except for the presence of preneoplastic basophilic foci in two fish previously fed 57.6 microg Se/g diet, normal liver morphology was observed in splittail in all treatments at the end of 21-wk depuration. Prevalences of kidney lesions were increased in fish previously fed 26.0 and 57.6 microg Se/g diets at 3 and 7 wk, and decreased at 13 and 21 wk of depuration. No kidney lesions were observed in fish previously fed 12.6 microg Se/g diet or less. In conclusion, growth of splittail previously fed a diet containing 57.6 microg Se/g was still affected at the end of 21-wk depuration. The 21-wk depuration was not long enough for muscle Se concentrations to return to basal levels in fish previously fed 12.6 or more microg Se/g diet. Deleterious health effects of Se persisted in fish previously fed diets with 26.0 or more microg Se/g diet. Current results suggest that splittail that survived the 9-month exposure to 12.6 or less microg Se/g diet under current laboratory conditions is likely to thrive if Se in diet was reduced to control concentration.