Studies On Protein And Energy Requirements Of Juvenile Yellow Catfish, Pelteobagrus Fulvidraco Rich

Seventeen semi-purified diets were formulated to estimate the protein and energy requirements of juvenile yellow catfish (initial average weight 2.0g) by a 6-week feeding trial. Each diet was fed in triplicate to groups of yellow catfish at 4%~5% of body weight, twice a day. The main results were summarized as follows:1. Eight isoenergetic diets (20.01MJ gross energy/kg) with protein contents ranging from 20% to 55% at an increment of 5% were used. Based on weight gain rate (WGR), a broken-line model fitted by least squares showed that the dietary protein requirement for the optimum growth of juvenile yellow catfish was 37.49%, and 10.37% for the weight maintenance, that is 1.50g -1.8 Ig protein requirement per lOOg body weight per day for the optimum growth, 0.41g~0.52g/100g-d for maintenance. When dietary protein content was as low as 20%, WGR and body crude lipid contents were significantly lower. But when protein level increased to 55%, WGR tend to decrease, body crude lipid content was significantly higher (P<0.05). Whether the dietary protein content was low (20%) or high (55%), protein deposit rate (PDR) were significantly lower (PO.05).2. Using the second-order polynomial regression analysis, the optimum gross energy and the optimum energy to protein ratio in diets for juvenile yellow catfish were estimated to be 19.89MJ/kg~20.06MJ/kg and 46.35kJ/g~52.93kJ/g based on WGR, PDR and energy retention rate (ERR) of the juveniles fed twelve diets with four energy levels (18.87MJ/kg, 20.01MJ/kg, 21.39MJ/kg and 22.81MJ/kg) and three protein contents (35%, 40%, 45%).3. The optimum dietary protein requirement was related to dietary gross energy (DGE). When DGE decreased from 20.01MJ/kg to 18.87MJ/kg, the dietary protein content should increase to 40% for improved growth of juvenile yellow catfish. Withthe diets containing high gross energy levels (21.39MJ/kg, 22.81MJ/kg), WGR, PDR and ERR of juvenile decrease and FCE increase as dietary protein contents increased, indicating low protein requirement of juvenile yellow catfish with diets of high energy levels.4. The optimum DGE was related to dietary protein content as well. When the dietary protein content was 35%, the optimum DGE for growth and feed utilization was 21.39MJ/kg. While the dietary protein content increased to 40% or more, the optimum DGE decreased to 18.87MJ/kg.5. When DGE was as high as 22.81MJ/kg, WGR, PDR and ERR were significantly lower, FCE was significantly higher (P<0.05) than other energy levels, indicating that diets with too high energy level would inhibit the growth and feed utilization of juvenile yellow catfish.6. DGE interacted with dietary protein content significantly (P<0.01) on growth and feed utilization of juvenile yellow catfish. Diet with low energy level (18.87MJ/kg) and low protein content (35%) resulted in poor growth of juvenile catfish and bad feed utilization, so did diets with high energy levels (21.39MJ/kg, 22.81MJ/kg) and high protein content (45%).7. Increased DGE from 18.87MJ/kg to 20.01MJ/kg or higher resulted in significant (P<0.05) decrease in body moisture and crude protein content, and body crude lipid content, increase at first and then decrease as DGE increased. The body crude lipid content was highest when DGE was 21.39MJ/kg.