An 8-week feeding trial was conducted to determine the dietary
tryptophan requirement of fingerling Indian catfish, Heteropneustes fossilis (6.10 ± 1.15 cm, 4.44 ± 0.50 g). Six isonitrogenous (40 g 100 g⁻¹) and isoenergetic (17.90 kJ g⁻¹)
amino acid test diets were formulated with gradation of 0.1 g 100 g⁻¹ containing graded levels of
L-tryptophan (0.04-0.54 g 100 g⁻¹, dry diet). Fish were stocked in triplicate groups, in 75-L circular trough with flow-through system and fed experimental diets at 4% BW/day twice daily. Maximum live
weight gain (258%), best feed conversion ratio (FCR) (1.54) and
protein efficiency ratio (PER) (1.62) were obtained in fish fed diet containing 0.34 g 100 g⁻¹
tryptophan. However, quadratic regression analysis of
weight gain, FCR, PER and body
protein deposition (BPD) data indicated requirements for dietary
tryptophan at 0.37, 0.33, 0.32 and 0.33 g 100 g⁻¹ of dry diet, respectively. Significantly (P < 0.05) higher body
protein, minimum moisture and intermediate fat contents were recorded at 0.34 g 100 g⁻¹ dietary
tryptophan diet. Ash content was not significantly different (P > 0.05) among treatments except for diets 0.04 and 0.14 g 100 g⁻¹. Excellent somatic and haematological indices values were obtained at the requirement level. Based on above results, it is recommended that the diet for H. fossilis should contain
tryptophan at 0.32 g 100 g⁻¹, dry diet, corresponding to 0.80 g 100 g⁻¹
dietary protein for optimum growth and efficient feed utilization.