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

Abstract

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 °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.