Effects of dietary taurine on growth, immunity and hyperammonemia in juvenile yellow catfish Pelteobagrus fulvidraco fed all plant protein diets
Abstract An 84 day feeding trial was conducted to determine the dietary taurine requirement of juvenile yellow catfish Pelteobagrus fulvidraco Six isonitrogenous and isolipidic diets (40% protein and 7% lipid) were formulated to contain six graded dietary taurine levels ranging from 0.02 to 2.55% (dry weight) in about 0.5% increments. Each diet was randomly assigned to triplicate groups of 30 juvenile fish (5.18 0.14 g) twice daily to apparent satiation. The results indicated that weight gain and red blood cell, hemoglobin and hematocrit significantly increased as dietary taurine levels increased up to 1.09% but were not significantly different from 1.09 to 2.55% taurine diets. Serum total protein, triglyceride, cholesterol and alanine aminotransferase decreased with increasing dietary taurine levels, on the contrary, serum superoxide dismutase, catalase and glutathione peroxidase activities, lysozyme activity, phagocytic index, respiratory burst and total immunoglobulin content increased. Fish fed the taurine deficient diet (0.02% of dry diet) showed the highest hepatosomatic index, whole body lipid, white blood cell count and malondialdehyde content. Cumulative mortality in fish fed 0.02 0.48% taurine diets were higher than in fish fed 1.09 2.55% taurine diets after injection with ammonium acetate at hour 24. After the challenge test, fish brain ammonia, glutamate and glutamine contents decreased as dietary taurine levels increased up to 1.09% but no significant differences were found with a further increase in dietary taurine. The two straight broken line regression analysis on weight gain against dietary taurine levels indicated that the optimal dietary taurine requirement was estimated to be 1.09% of the diet. Based on fish growth, immunity and resistance against hyperammonemia, the level of 1.09% taurine in the all plant protein diet is recommended in juvenile yellow catfish. Statement of relevance This study will be useful in developing amino acid balanced diets for intensive culture of yellow catfish.