An 8-week feeding experiment was conducted to evaluate the dietary leucine requirement of ¢ngerling Indian major carp, Labeo rohita (3.50 AE 0.04 cm; 0.40 AE 0.02 g) using amino acid test diets (40% crude protein; 17.90 kJ g À1 gross energy) containing casein and gelatin as intact protein sources and L-crystalline amino acids. Growth performance and biochemical parameters were assessed by feeding six amino acid test diets supplemented with graded concentrations of leucine (0.75, 1.0, 1.25, 1.50, 1.75 and 2.0 g per 100 g) to triplicate groups of ¢ngerlings to apparent satiation divided over two feedings at 07:00 and 17:30 hours. Performance of the ¢sh was evaluated on the basis of live weight gain, feed conversion ratio (FCR), protein e⁄ciency ratio (PER) and body protein deposition (BPD) data. Maximum live weight gain (315%), best FCR (1.35), highest PER (1.86) and BPD (33.9) were recorded at 1.50 g per 100 g dietary leucine. Statistical analysis of live weight gain, FCR, PER and BPD data re£ected signi¢cant di¡erences (Po0.05) among treatments. Live weight gain, FCR, PER and BPD data were also analysed using second-degree polynomial regression analysis to obtain more accurate leucine requirement estimate which was found to be at 1.57, 1.55, 1.52 and 1.50 g per 100 g of dry diet, corresponding to 3.92, 3.87, 3.80 and 3.75 g per 100 g of dietary protein respectively. Based on the quadratic regression analysis of the live weight gain, FCR, PER and BPD data, the optimum requirement of ¢ngerling L. rohita for leucine is estimated to be in the range of 1.50^1.57 g per 100 g of the dry diet, corresponding to 3.75^3.92 g per 100 g of dietary protein.

Dietary arginine requirement of Heteropneustes fossilis fry (3.0 ± 0.5 cm; 5.1 ± 0.3 g) was determined by feeding casein‐gelatin‐based isonitrogenous (400 g kg−1 crude protein) and isocaloric (17.97 kJ g−1) amino acid test diets containing graded levels of l‐arginine (15, 17, 19, 21, 23 and 25 g kg−1 dry diet) for 12 weeks. Maximum absolute weight gain (AWG) (44.4), best feed conversion ratio (FCR) (1.22), highest protein retention efficiency (PRE%) (41%), energy retention efficiency (ERE%) (75%), best condition factor, hepatosomatic index and viscerosomatic index were noted at 21 g kg−1 arginine of the dry diet. Maximum body protein (189.8 g kg−1) was also obtained in fish fed above diet. Highest haematocrit value (35%), Hb concentration (9.54 g dL−1), RBC count (3.44 × 109 mL−1) and lowest Erythrocyte sedimentation rate (ESR) (1.93 mm h−1) were obtained at the above level of arginine in the diet. AWG, FCR, PRE% and ERE% data were analysed using broken‐line and an exponential fit to obtain more precise dietary arginine requirement. On the basis of broken‐line and exponential analyses of AWG, FCR, PRE and ERE data, inclusion of dietary arginine in the range of 20.4–22.6 g kg−1 dry diet, corresponding to 51–56.5 g kg−1 dietary protein, is recommended for formulating arginine‐balanced feeds for rearing H. fossilis fry.

Dietary valine requirement of Indian major carp, Labeo rohita Hamilton, fry (3.0 ± 0.02 cm, 0.16 ± 0.03 g) was determined using dose-response method. Fishes were fed six isonitrogenous [40% crude protein (CP)] and isocaloric (4.28 kcal g )1 , Gross Energy (GE)) amino acid test diets containing casein, gelatin, and L L-crystalline amino acids with graded levels of valine (0.75, 1.00, 1.25, 1.50, 1.75, and 2.00% dry diet) at 5% body weight for 6 weeks in triplicate groups twice a day at 07.00 and 17.30 hours. Live weight gain (158.52%), feed conversion ratio (FCR, 1.70), specific growth rate (SGR, 2.25), and protein efficiency ratio (PER, 1.46) were significantly (P < 0.05) higher in fish fed a diet containing 1.5% of the dietary valine (diet IV). Second-degree polynomial regression analysis of the live weight gain and FCR data indicated the dietary valine requirement at 1.63 and 1.5% of the dry diet, corresponding to 4.0 and 3.75% of dietary protein. Maximum carcass protein, minimum moisture, and fat were recorded at 1.5% of the dietary valine level, except carcass ash, which remained constant throughout the treatments. No mortality was observed during the entire length of the feeding trial. On the basis of FCR and protein deposition data, it is recommended that dietary valine inclusion at 1.5% of dry diet, corresponding to 3.75% of dietary protein, is optimal for the growth of L. rohita fry.

An 8-week feeding experiment was conducted to quantify the dietary isoleucine requirement of fingerling Indian major carp, Labeo rohita (3.50 ± 0.04 cm; 0.40 ± 0.02 g) using amino acid test diets (400 g kg )1 crude protein; 17.90 kJ g )1 gross energy) containing casein, gelatin and L L-crystalline amino acids. Six dietary treatments supplemented with graded levels of isoleucine (7.5, 10.0, 12.5, 15.0, 17.5 and 20.0 g kg )1 ), in gradations of 2.5 g kg )1 diet, were fed to triplicate groups of fingerlings to apparent satiation divided over two feedings at 07:00 and 17:30 h. Performance of the fish was evaluated on the basis of live weight gain, feed conversion ratio (FCR), protein efficiency ratio (PER), specific growth rate (SGR) and protein productive value (PPV). Statistical analysis of live weight gain, FCR, PER, SGR and PPV reflected significant differences among treatments. Live weight gain and conversion efficiencies were best with isoleucine at 15.0 g kg )1 of diet. Live weight gain, FCR, PER, SGR and PPV data were also analysed using seconddegree polynomial regression analysis to obtain more accurate isoleucine requirement estimate which was found to be at 15.9, 15.3, 15.2, 15.8 and 15.7 g kg )1 of dry diet, corresponding to 39.8, 38.3, 38.0, 39.5 and 39.3 g kg )1 of dietary protein respectively. Based on the quadratic regression analysis of the live weight gain, FCR, PER, SGR and PPV, the optimum level of isoleucine for fingerling L. rohita is in the range of 15.2-15.9 g kg )1 of dry diet, corresponding to 38.0-39.8 g kg )1 of dietary protein. Maximum body protein, minimum moisture and fat were noted at 15.0 g kg )1 of dietary isoleucine while the body ash remained constant among all the treatment levels. No mortality was recorded during the duration of the experiment. KEY WORDS

Optimum ration size of Indian major carp, Cirrhinus mrigala fingerlings was determined by feeding purified diet (40% crude protein (CP); 3.61 kcal g−1) at five ration sizes (2%, 4%, 6%, 8% and 10% of body weight per day) for 6 weeks. Feeding trial was conducted in triplicate. Fishes were randomly stocked at the rate of 20 fish per trough fitted with water flow‐through system. The best feed conversion ratio (FCR), specific growth rate (%) and protein efficiency ratio (PER) were evident at the ration size of 4–6% body weight. Second‐degree polynomial regression analysis of the FCR, PER, and protein and energy retention data indicated the breakpoints at ration size of 5.16%, 5.24%, 5.52% and 5.42% body weight per day. Carcass composition of fish fed different ration sizes varied significantly. Maximum carcass protein and minimum moisture content were noticed at 4% and 6% ration levels. A linear increase in fat content was evident with increasing ration levels up to 6% body weight. Ash content remained insignificantly different among various ration levels except at 2%, showing the significantly highest value. Water temperature, dissolved oxygen, free carbon dioxide, pH and total alkalinity were recorded regularly during the length of the experiment. No mortality was observed during the feeding trial. Based on the above results, it is recommended that feeding in the range of 5–5.5% body weight per day corresponding to 20 g protein and 181 kcal energy to 22 g protein and 199 kcal energy per kg of the diet per day is optimum for the growth and efficient feed utilization of C. mrigala.

Effect of varying dietary lysine levels on growth, feed conversion, nutrient retention, lysine retention efficiency and haematological indices of Heteropneustes fossilis fry (2.97 ± 0.11 cm; 4.78 ± 0.31 g) was studied by conducting a 12‐week feeding trial. Isonitrogenous (450 g kg−1 CP) and isocaloric (17.97 kJ g−1 GE) amino acid test diets with graded concentrations of l‐lysine (18, 20, 22, 24, 26, 28 g kg−1 dry diet) were fed to triplicate groups of fish to apparent satiation twice daily at 17 and 17:30 h. Maximum thermal growth coefficient (TGC, 0.82), best feed conversion ratio (FCR, 1.28) highest protein retention efficiency (PRE, 36%), energy retention efficiency (ERE, 79%) and lysine retention efficiency (LRE, 75%) were noted at 24 g kg−1 lysine of dry diet. Body protein was also found to be in line with growth data and peaked at 24 g kg−1 lysine of dry diet. Similarly, superior somatic and haematological indices were exhibited by the groups fed dietary lysine at 24 g kg−1 of the dry diet. However, exponential analysis of dietary lysine intake against TGC, lysine retention and protein retention indicated that inclusion of dietary lysine in the range of 13.24–14.14 g kg−1 dry diet, corresponding to 29.42–31.42 g kg−1 dietary protein, is essential for faster growth of this fish.

Dietary histidine requirement of fry African catfish, Clarias gariepinus (2.57 ± 0.02 cm; 0.22 ± 0.03 g) was quantified by feeding casein–gelatin‐based isonitrogenous (40% crude protein) and isocaloric (17.90 kJ g−1 gross energy) amino acid test diets with graded levels of histidine (0.25%, 0.30%, 0.35%, 0.40%, 0.45% and 0.50% dry diet) in eighteen 80 L indoor circular aqua‐coloured troughs provided with the flow‐through system for 12 weeks. Maximum absolute weight gain (2.66), best feed conversion ratio (1.29), highest protein efficiency ratio (1.94), protein retention efficiency (34%) and energy retention efficiency (70.4%) were achieved at 0.40% dietary histidine. Broken‐line and non‐linear regression models were adopted to assess dietary histidine requirement for C. gariepinus. When analysed using broken‐line regression model these parameters were also best at 0.40% dietary histidine corresponding to 1.0% protein, respectively, whereas using second‐degree polynomial regression analysis, histidine requirement was obtained at 0.42%, 0.41%, 0.40%, 0.41% and 0.41% of dry diet, corresponding to 1.05%, 1.02%, 1.0%, 1.02% and 1.02% protein respectively. Based on the broken‐line and second‐degree polynomial regression analyses of the growth and nutrient retention data, optimum histidine requirement of fry C. gariepinus was found to be in the range of 0.40–0.42% dry diet, corresponding to 1.0–1.05% of dietary protein.

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