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Growth, reproductive performance, muscle and egg composition were investigated in grass carp, Ctenopharyngodon idella (Valenciennnes), fed hydrilla or formulated diets with varying protein levels. Five experimental diets, with varying levels (20%, 25%, 30%,35% and 40%) of crude protein (CP), were used. One of the ¢sh groups was fed hydrilla. Fish (44.1 AE 0.3 cm; 913 AE 9 g) were stocked (20 tank À1 ) in outdoor concrete tanks (20 Â 10 Â 1.5 m) in duplicate, and fed to satiation, twice daily, at 09:00 and 17:00 hours for the experimental duration of 360 days. High (Po0.05) weight gain was recorded in ¢sh fed 30% and 35% CP diets. However, values for gonadosomatic index (GSI), egg diameter, relative fecundity (eggs kg À1 body weight), fertilizability and hatchability (%) were comparable (P40.05) in ¢sh at ! 25% of dietary protein intake. Hydrilla-fed ¢sh exhibited lower (Po0.05) values for the measured parameters. Crude protein content in muscle increased with dietary protein level. Highest (Po0.05) muscle protein was obtained in ¢sh fed 35% CP diet. Muscle fat was comparable (P40.05) among ¢sh receiving formulated diets. Ash content was not signi-¢cantly (P40.05) di¡erent among ¢sh of di¡erent dietary groups. Moisture content in ¢sh fed formulated diets, with the exception of 20% CP diet, did not vary signi¢cantly (P40.05). Eggs of ¢sh fed formulated diets contained higher CP and fat contents than those of hydrilla-fed ¢sh. High (Po0.05) moisture content was noted in the eggs of hydrilla-fed ¢sh. Ctenopharyngodon idella fed formulated diet, with a minimum of 25% CP, showed better reproductive performance than those fed hydrilla.

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Indian major carp ¢ngerling, Cirrhinus mrigala (3.85 AE 0.75 cm, 0.52 AE 0.21g), were fed isonitrogenous and isocaloric diets (40% crude protein, 4.28 kcal g À 1 , gross energy) containing casein, gelatin and crystalline amino acids with graded levels of L-threonine (1.00, 1.25, 1.50, 1.75, 2.00 and 2.25 g100 g À 1 , dry diet) to determine the dietary threonine requirement. The feeding trial was conducted in triplicate for 8 weeks. Diets were fed twice a day at 08:00 and 16:00 hours at 5% body weight day À 1 . The ration size and feeding schedule were worked out before the start of the feeding trial.Highest weight gain (304%) and best feed conversion ratio (1.43) were evident in ¢sh fed diet containing 1.75% dietary threonine. Second-degree polynomial regression analysis of weight gain, feed conversion ratio and protein e⁄ciency ratio data indicated the dietary threonine requirement to be at 1.84%, 1.81% and 1.78%, respectively, corresponding to 4.60%, 4.52% and 4.45% of dietary protein. Minimum carcass moisture, fat and maximum carcass protein were evident in ¢sh fed 1.75% threonine level. However, ash content did not a¡ect body composition, except the 1.00% threonine level, which showed a signi¢cantly higher ash content value. Based on the above results, it is recommended that the diet for C. mrigala should contain threonine at 1.80 g100 g À 1 dry diet, corresponding to 4.50 g100 g À 1 dietary protein for optimum growth and e⁄cient feed utilization. Cirrhinus mrigala, dietary threonine requirement I Ahmed et al.Ã Mean value of three replicate AE SEM. Mean values with the same superscripts are insigni¢cantly di¡erent (P40.05).Aquaculture Research, 2004, 35, 162^170 Cirrhinus mrigala, dietary threonine requirement I Ahmed et al.