Dietary amino acid L-methionine requirement of fingerling Indian catfish, Heteropneustes fossilis (Bloch-1974) estimated by growth and haemato-biochemical parameters

An 8 weeks feeding trial was conducted to determine the dietary methionine requirement of fingerling Indian catfish, Heteropneustes fossilis (6.08 +/- 0.95cm; 4.33 +/- 0.52g). Six isonitrogenous (40%) and isoenergetic (17.90kJg(-1) GE) amino acid test diets were formulated with gradation of 0.25g 100g(-1)containing graded levels of (L)-methionine (0.30, 0.55, 0.80, 1.05, 1.30 and 1.55g 100g(-1), dry diet) with 0.40g 100g(-1) constant level of cystine. Twenty fish were stocked in triplicate groups, in 75-L circular trough with continuous flow-through system and fed experimental diets at 4% BW/day twice daily, at 08:00 and 18:00hours. Maximum live weight gain (296%), best feed conversion ratio (1.56) and protein efficiency ratio (1.60) were occurred at 1.05g 100g(-1) methionine, beyond which they showed declining tendency. However, quadratic regression analysis of weight gain, feed conversion ratio (FCR), protein efficiency ratio (PER) and body protein deposition (BPD) data indicated requirement for methionine at 1.15, 1.08, 1.06 and 1.05g 100g(-1) of dry diet respectively. Significantly (P<0.05), higher whole body protein content, minimum moisture and intermediate fat contents were recorded at 1.05g 100g(-1) dietary methionine level. Ash content remained insignificantly (P>0.05) low among all the treatments, excepting at diet I and diet II. Body protein deposition was also found to be significantly (P<0.05) higher at 1.05g 100g(-1) methionine level. Best somatic and haematological indices values were also obtained at the requirement level. Based on above results, it is recommended that the diet for young H. fossilis should contain methionine at 1.09g 100g(-1) dry diet, corresponding to 2.73g 100g(-1) dietary protein with 0.40g 100g(1) cystine concentration for optimum growth and efficient feed utilization. Thus, the total sulphur amino acid requirement of H. fossilis would be (1.09+0.40) 1.49g 100g(-1) of dry diet, corresponding to 3.73g 100g(-1) of dietary protein.