Dietary tryptophan requirement of fingerling Catla catla (Hamilton) based on growth, protein gain, RNA/DNA ratio, haematological parameters and carcass composition

A 12-week feeding trial was conducted in eighteen 70 L indoor polyvinyl circular troughs provided with a water flow-through system (1-1.5 L min(-1)) at 28 +/- 1 degrees C to evaluate the dietary tryptophan requirement of fingerling Catla catla (3.45 +/- 0.24 cm; 0.60 +/- 0.13 g). Six casein-gelatin-based amino acid test diets (330 g kg(-1) crude protein; 13.6 kJ g(-1) digestible energy) containing graded levels of L-tryptophan (1.0, 1.4, 1.9, 2.3, 2.8, 3.4 g kg(-1) dry diet) were fed to triplicate groups of fish near to satiation at 08: 00, 12: 30 and 17: 30 h. Absolute weight gain, feed conversion ratio, protein gain, RNA/DNA ratio, hepatosomatic index, viscerosomatic index, condition factor and haematological indices improved with the increasing levels of tryptophan from 1.0 to 2.3 g kg(-1) of dry diet. Significantly higher carcass protein was obtained at 2.3 g tryptophan per kilogram of the dry diet. Exponential analysis of absolute weight gain, feed conversion ratio, protein gain and RNA/DNA ratio against dietary tryptophan levels at 95% maximum and minimum responses displayed the tryptophan requirement at 2.5, 2.3, 2.5 and 2.1 g kg(-1) dry diet, respectively. Inclusion of dietary tryptophan in the range of 2.1-2.5 g kg(-1) dry diet, equivalent to 6.4-7.6 g kg(-1) dietary protein, is recommended in formulating tryptophan-balanced feed for the culture of this fish species.