COMPARATIVE STUDIES ON NITROGEN BUDGET AND ENERGY BUDGET OF HYBRID CARP AND HYBRID TILAPIA FED DIETS WITH DIFFERENT QULITIES

A 53-day growth trial was conducted to investigate nitrogen budget and energy budget of hybrid carp (Cyprinus carpio var.♀×C.carpio var.♂)and hybrid tilapia (Oreochromis niloticus♀×O.aureus♂)fed diets with different quality.Low quality diet (LQ diet ) and high quality diet (HQ diet)were tested.LQ diet contained 34.25%dietary protein which is mainly from soybean meal while HQ diet contained 45.44% dietary protein which is mainly from fish meal.The initial average body weight of fishes was from 3.13g to 3.87g.The trial was carried out in a system consisting of 12 self-circulation tanks (volume:150 L).During the experiment, dechlorinated tap water was added into each tank at the rate of approximate 1500mL/min.Dissolved oxygen was maintained above 5.76mg/L,ammonia below 0.098mg/L and the natural temperature 24.2-28.5℃.The light is sunshine light. At the beginning of the experiment,the fish were deprived of food for one day, and 25 hybrid carp of hybrid tilapia were randomly selected, batch-weighed and allocated into each tank.Three tanks were assigned randomly to each combination of fish strain and diet.During the experiment, the fish were fed to satiation twice a day (at 9:00 and 15:00),and uneaten feed was collected 1h after feeding and dried.Feces were collected twice a day (at 11:00 and 16:45)from the bottoms of tanks and dried at 70℃. The effects of diet and fish strain were analyzed ty two-way analysis of variance (ANOVA).Multiple comparisons (Duncan’s procedure)were used to evaluate the significance of strains or diets. The results showed that,the nitrogen budget and energy budget were significantly affected by both diet and fish strain. When fed LQ diet,the proportion of nitrogen and energy of food deposited in growth in hybrid tilapia was higher than that in hybrid carp,while the proportion of excretive nitrogen and excretive energy and metabolism energy in hybrid tilapia was lower than that in hybrid carp. When fed HQ diet,the proportion of growth nitrogen and growth energy in hybrid tilapia was higher than that in hybrid carp, while hybrid tilapia had lower proportion of fecal nitrogen and fecal energy than hybrid carp. In hybrid carp,proportion of growth nitrogen and growth energy were not affected by diet quality while HQ diet resulted in lower excretive nitrogen and metabolism energy than LQ diet.Diet quality did not affect nitrogen budget in hybrid tilapia while HQ diet resulted in higher growth energy and excretion energy and lower metabolism energy than LQ diet. In conclusion,compared to hybrid tilapia,hybrid carp showed poorer utilization of nitrogen and energy when fed two diets with different quality.