Dietary histidine requirement of fingerling Indian major carp, Cirrhinus mrigala (Hamilton)

An 8-week growth trial was conducted to determine the dietary histidine requirement of the Indian major carp, Cirrhinus mrigala fingerling (length 4.22 ± 0.45 cm; weight 0.61 ± 0.08 g; n = 40). Isonitrogenous (400 g kg-1 crude protein) and isoenergetic (17.90 kJ g-1 gross energy) diets with graded levels of l-histidine (2.5, 5.0, 7.5, 10.0, 12.5 and 15.0 g kg-1 dry diet) were formulated using casein and gelatin as a source of intact protein, supplemented with l-crystalline amino acids. Twenty fish were randomly stocked in 70-L indoor polyvinyl circular fish tank (water volume 55-L, water exchange rate 1-1.5 L min-1) and fed experimental diets at the rate of 5% of their body weight/day divided over two feedings at 08:00 and 16:00 h. Maximum live weight gain (295%), best feed conversion ratio (FCR) (1.48) and protein efficiency ratio (PER) (1.69) occurred at 7.5 g kg-1 of dietary histidine level. When live weight gain, FCR and PER data were analysed using second-degree polynomial regression, the break points indicated histidine requirements at 9.4, 8.6 and 8.5 g kg-1 of dry diet respectively. Significantly (P < 0.05) higher whole body protein and low moisture values were recorded at 7.5 g kg-1 histidine level. Body fat increased significantly (P < 0.05) with increasing histidine levels. However, at 7.5 and 10 g kg-1 histidine diets body fat did not differ (P > 0.05) to each other. Ash content of fish fed diets containing various levels of histidine did not differ except at 2.5 and 5.0 g kg-1 inclusion levels where significantly (P < 0.05) higher ash was recorded. Protein deposition was also found to be significantly (P < 0.05) higher in the 7.5 g kg-1 histidine diet. Based on the polynomial regression analysis of FCR and PER data, it is recommended that the diet for fingerling C. mrigala should contain histidine at 8.5 g kg-1 of dry diet, corresponding to 21.25 g kg-1 of dietary protein for optimum growth and efficient utilization of feed.