EFFECT OF VARYING LYSINE TO ENERGY RATIO ON THE GROWTH, PROTEIN RETENTION EFFICIENCY, RNA/DNA RATIO, HAEMATOLOGICAL PARAMETERS AND CARCASS COMPOSITION OF FINGERLING Labeo rohita  

Indian major carp, Labeo rohita is one of the important preferred species in the Asian sub-continent because of its rapid growth, acceptability to prepared feeds and high market value. This fish has the ability to utilize plant feedstuffs efficiently which are known to be deficient in essential amino acids, adversely affecting the growth and feed conversion efficiency. The availability of dietary energy plays an important role in utilisation of amino acids. Hence, there is a dire need to determine the dietary amino acid to energy requirement. There is no information available on optimum amino acid to energy ratio. The present study was, therefore, conducted to determine the optimum dietary lysine to energy ratio in L. rohita.

A six-week feeding trial was conducted in thirty 70-L indoor tanks (water volume 55 L) provided with a water flow-through system (1-1.5 L/min) to optimise dietary lysine to energy ratio in the diet of fingerling L. rohita (3.51±0.02 g). Casein-gelatin based experimental diets (35 g/100 g crude protein) with three levels of L-lysine (1.60, 2.00 and 2.40 g/100 g) and three levels of digestible energy (380, 400 and 420 kcal DE /100 g) were used in a 3 × 3 factorial design to provide nine different dietary lysine to energy ratios (4.20, 4.07, 3.81, 5.29, 5.15, 4.86, 6.32, 5.97 and 5.67 mg lysine/kcal DE). A tenth diet as a control with 40 g/100 g CP, 2 g lysine/100g,  400 kcal DE/100 g  with a lysine to energy ratio of  4.99 mg lysine/kcal DE was also formulated. The diets were hand-fed to triplicate groups of fish to apparent satiation at 08:00, 12:30 and 17:30 h. Absolute weight gain, feed conversion ratio, protein retention efficiency, carcass composition, RNA/DNA ratio and haematological indices were found to be optimal in fish fed with diet containing 2.04 g/100 g dietary lysine, 385 kcal DE/100 g and a lysine to energy ratio of 5.29 mg lysine/kcal DE (diet 4). The growth performance of fish fed diet 4 or 5 with a lysine to energy ratios of 5.29 or 5.15 and a CP level of 35 g/100 g was not significantly different from the group fed the control diet (diet 10) with 4.99 lysine to energy ratio and 40 g/100 g CP. This similar growth performance indicate that the CP as such is not a growth-limiting factor, and fish require adequate levels of amino acids and energy. Based on the growth performance (Table 1), haematological indices and carcass composition, optimum dietary lysine to energy ratio is recommended at 5.29 mg lysine/kcal DE (2.04g/100 g lysine with 385 kcal /100 g DE) for fingerling L. rohita.