Dietary threonine requirement of fingerling I ndian major carp, C atla catla ( H amilton) estimated by growth, protein retention efficiency, threonine deposition, haematological parameters and carcass composition

A 12‐week feeding trial was conducted to determine the dietary threonine requirement of fingerling I ndian major carp, C atla catla (3.35 ± 0.11 cm; 0.59 ± 0.06 g). Six casein‐gelatin based (33% crude protein; 3.23 kcal g −1 digestible energy) amino acid test diets with graded levels of analysed threonine (0.74%, 0.96%, 1.21%, 1.48%, 1.72% and 1.93% dry diet) were fed to satiation to triplicate groups of fish. Absolute weight gain (g per fish), feed conversion ratio, protein retention efficiency, threonine deposition, RNA / DNA ratio and carcass protein significantly improved with the increase in dietary threonine and peaked at 1.48% of the dry diet. Haematological indices were also found to be best in fish fed at 1.48% threonine diet. Quadratic regression analysis of absolute weight gain, feed conversion ratio, protein retention efficiency, threonine deposition, RNA / DNA ratio, carcass protein, haemoglobin (g dL −1 ), haematocrit (%) and RBC s (10 6  × mm −3 ) at 95% of maximum and minimum response exhibited the threonine requirement of fingerling C . catla between 1.35% and 1.48% dry diet, corresponding to 4.09–4.48% dietary protein. Present finding would be useful in formulating threonine‐balanced feeds for the intensive culture of C . catla .