Dietary selenium requirement and toxicity levels in juvenile Nile tilapia, Oreochromis niloticus

Abstract

A 10-week feeding trial was conducted to evaluate the dietary selenium (Se) requirement and toxicity levels in juvenile Nile tilapia, Oreochromis niloticus. Graded levels of selenomethionine were added to the basal diet at 0, 0.25, 0.5, 0.75, 1.0, 2.0, 4.0, 8.0 and 16.0 mg Se/kg diet giving 0.30 (Se0.30), 0.55 (Se0.55), 0.73 (Se0.73), 0.82 (Se0.82), 1.04 (Se1.04), 2.06 (Se2.06), 2.95 (Se2.95), 6.31 (Se6.31) and 14.7 (Se14.7) mg Se/kg diet respectively. Fish averaging 1.85 ± 0.1g (Mean ± SD) were fed one of the nine experimental diets in triplicate groups. After the feeding trial, weight gain (WG), specific growth rate (SGR) and feed efficiency (FE) of fish fed Se2.06 were significantly higher than those of fish fed the other diets (P < 0.05). Fish fed Se2.95, Se6.31 and Se14.7 diets showed significantly higher crude protein than fish fed the other diets. Se concentrations of liver, muscle and gill tissues were dose dependent although liver Se concentrations were significantly higher than muscle and gill. Lysozyme activities of fish fed Se0.30 diet were significantly lower than those fish fed the other diets. Myeloperoxidase (MPO) and superoxide dismutase (SOD) activities of fish fed Se6.31 diet were significantly higher than those of fish fed the other diets. Glutamyl pyruvic transaminase (GPT), glutamyl oxaloacetic transaminase (GOT) and glucose levels from fish fed Se14.7 were significantly higher than those from fish fed the other diets. Broken-line regression analysis of WG indicated that the minimum Se requirement was 1.06 mg Se/kg diet. Based on these results, it can be concluded that the dietary Se requirement could be greater than 1.06 but less than 2.06 mg Se/kg for maximal growth for juvenile Nile tilapia. And also the dietary toxic Se level could be greater than 6.31 but less than 14.7 mg Se/kg diet for juvenile Nile tilapia, Oreochromis niloticus.