Dietary carbohydrate requirement of lemon fin barb hybrid (Barbonymus gonionotus Bleeker 1849 ♀ X Hypsibarbus wetmorei Smith 1931 ♂) fingerlings

Carbohydrates are the widely available and cheap source of dietary energy. The optimal inclusion of carbohydrate in a fish diet can help in reducing the cost of feed and farm operation. The present study was conducted to determine the dietary carbohydrate requirement of lemon fin barb hybrid including the optimal inclusion, the best carbohydrate source and the optimal starch-fiber ratio. Three separate feeding trials were conducted in 100 l glass aquaria in which fish were fed at 4-6% body weight twice a day for 60 days. All treatments were triplicated. Growth, survival, hepatosomatic index, viserosomatic index, body composition and nutrient retention of the fish were estimated. In Experiment I, five isonitrogenous (30% protein) and isolipid (4%) test diets containing varying carbohydrate levels (20, 25, 30, 35 and 40 %) were tested. Tapioca starch was used as the carbohydrate source. No mortality was observed in the experiment. The maximal growth was achieved when lemon fin barb hybrid was fed 35% carbohydrate. However, the polynomial regression analysis indicated that the optimal dietary carbohydrate of the barb hybrid was 33.5%. The fish growth significantly dropped when the hybrid was fed more than 35% carbohydrate. In Experiment II, five isonitrogenous (30% protein) and isolipid (4%) diets containing 35% carbohydrate with corn, tapioca and sago starches, and wheat and rice flour as carbohydrate starch source were tested. The results indicated that carbohydrate sources have no significant effect on the survival, growth and other physiological parameters of this hybrid. In Experiment III, five isonitrogenous (30%) protein, isolipid (4%) diets containing 35% carbohydrate with varying starch:fiber ratios were tested. The results indicated that fish fed 30:5 starch-fiber ratio exhibited the highest growth but the hybrid fish were able to utilise fiber up to 10% diet (25% starch) without affecting fish growth and other physiological parameters. In conclusion, lemon fin barb hybrid fingerlings could utilise a wide range of carbohydrate sources and required 33.5% carbohydrate at 6:1 starch-fiber ratio in its diet with 30% protein, 4% lipid and gross energy 17 kJ g-1 for the optimal growth and best feed efficiency.

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