Five iso-energetic (15.05 MJ kg )1 ) semi-purified diets with graded levels of crude protein, i.e. 200 (D-1), 250 (D-2), 300 (D-3), 350 (D-4) and 400 (D-5) g kg )1 diet were fed to Puntius gonionotus fingerlings (average weight 0.88 ± 0.03 g) in triplicate groups (15 healthy fish per replicate) for a period of 90 days to determine the optimum protein requirement of the fish. Fifteen flowthrough cement tanks of 100-L capacity with a flow rate of 0.5 L min )1 were used for rearing the fish. Specific growth rate (SGR), food conversion (food gain) ratio (FCR), nutrient digestibility and retention, digestive enzyme activity, RNA : DNA ratio and tissue composition were used as response parameters with respect to dietary protein levels and feed intake. The mean weight gains of fish after 90 days were 10.84 ± 0.27, 11.07 ± 0.12, 14.09 ± 0.20, 11.27 ± 0.12 and 10.91 ± 0.25 g for D

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A 30-day study was undertaken to examine the proteinsparing effect of carbohydrate in diets for silver barb, Puntius gonionotus fry. Six semi-purified experimental diets were formulated with two levels of protein (200 and 250 g kg )1 diet) and three levels of carbohydrate (300, 340 and 380 g kg )1 diet). In addition to the six experimental diets, a diet containing the protein and carbohydrate requirement levels of 300 and 260 g kg )1 diet, respectively, as reported earlier for this species, was used as a reference diet. For each dietary treatment, 30 healthy fry of 20 days age (0.12 ± 0.01 g) were stocked in triplicate tanks using a flowthrough system. The fish were fed ad libitum four times a day to a level close to apparent satiation. Batch weighing of fish was done after 15 days of stocking to measure growth and general health status of the fish. The fish fed 250 g protein and 340 g carbohydrate kg )1 diet with a protein to energy ratio of 17.86 g protein MJ )1 performed equally well in terms of growth and nutrient utilization as the reference diet group. The study indicates that dietary protein can be reduced from 300 to 250 g kg )1 diet by increasing carbohydrate from 260 to 340 g kg )1 diet without sacrificing the growth of silver barb fry. KEY WORDS

Five iso-nitrogenous (300 g kg )1 diet) purified diets with graded level of lipid at 40 (D-1), 60 (D-2), 80 (D-3), 100 (D-4) and 120 (D-5) g kg )1 diet were fed to Puntius gonionotus fingerlings for 90 days to determine their dietary lipid requirement. Two hundred and twenty-five fingerlings (average weight 2.34 ± 0.03 g) were equally distributed in five treatments in triplicate groups with 15 fish per replicate. Fifteen flow-through cement tanks of 100 L capacity with a flow rate of 0.5 L min )1 were used for rearing the fish. Specific growth rate (SGR), feed conversion ratio (FCR), nutrient digestibility, retention, digestive enzyme activity, RNA : DNA ratio and whole-body composition were considered as the response parameters with respect to dietary lipid levels. Maximum SGR and minimum FCR with highest RNA : DNA ratio, whole-body protein content and digestive enzyme activity was found in D-3 group fed with 80 g kg )1 diet lipid. Nutrient digestibility was similar in all the groups irrespective of the dietary lipid level. Maximum protein and energy retention was recorded at 80 g kg )1 dietary lipid fed group. However, from the second-order polynomial regression analysis, the maximum growth of P. gonionotus fingerlings was found at 96.9 g lipid kg )1 diet. KEY WORDS

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Five iso‐nitrogenous (300 g crude protein kg−1 diet) semi‐purified diets with graded levels of carbohydrate at 220 (D‐1), 260 (D‐2), 300 (D‐3), 340 (D‐4) and 380 (D‐5) g kg−1 diet were fed ad libitum to Puntius gonionotus fingerlings (average weight 0.59±0.01 g) in triplicate groups (20 fish replicate−1) for a period of 90 days to determine the effect of the dietary carbohydrate level on the growth, nutrient utilization, digestibility, gut enzyme activity and whole‐body composition of fish. Fifteen flow‐through cement tanks of 100 L capacity with a flow rate of 0.5 L min−1 were used for rearing the fish. The maximum weight gain, specific growth rate, protein efficiency ratio, RNA:DNA ratio, whole‐body protein content, protease activity, protein and energy digestibility and minimum feed conversion ratio (FCR) were found in the D‐2 group fed with 260 g carbohydrate kg−1 diet. The highest protein and energy retention was also recorded in the same group. However, from the second‐order polynomial regression analysis, the maximum growth and nutrient utilization of P. gonionotus fingerlings was 291.3–298.3 g carbohydrate kg−1 diet at a dietary protein level of 300 g kg−1 with a protein/energy (P/E) ratio of 20.58 −20.75 g protein MJ−1.

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