EFFECT OF DIETARY REPLACEMENT OF FISHMEAL PROTEIN BY SOYBEAN MEAL PROTEIN ON GROWTH PERFORMANCE, METABOLISM AND IMMUNITY OF GIBEL CARP (<I>CARASSIUS AURATUS GIBELIO</I>)

Abstract

A 16-weeks growth was conducted to evaluate the effect of replacement of dietary fishmeal by soybean meal on growth performance, feed utilization,nitrogen metabolism and immunity in gibel carp. Four isonitrogenous and isocaloric diets were formulated. Each diet was fed to triplicate groups of fish with the initial weight at about 2.32 g. Soybean meal was used to replace 0 (Control, D1), 20% (D2), 80% (D3) and 100% (D4) of dietary fishmeal protein. The fish was reared in a semi-recirculating system. During the experiment, water temperature was 23-30 degrees C, photoperiod was 12D:12L with the light period from 08 : 00 to 20: 00, dissolved oxygen was above 5 mg/L, aninionia-N (NH4+-N plus NH3-N) was less than 0.5 mg/L, pH was about 6.4. Fish were fed to satiation twice daily (9:00 and 15:00). At the beginning of the experiment, healthy fish ( initial body weight about 2.32 g) were batch weighed after 24h feed deprivation and randomly distributed into the 12 tanks (40 fish per tank). The tanks were randomly assigned the four diets. Fifty fish were taken from the remaining fish and frozen for initial fish body chemical analysis. During the experiment, an excess amount of feed was fed to fish and uneaten feed were collected after I It in each feeding, dried at 60 degrees C and reweighed. Leaching rate of uneaten feed in tanks was estimated by placing weighed feeds into a tank without fish for I It and then recovering, drying and reweighing. The average leaching rate was used to calibrate the amount of uneaten feed. Faeces were collected after uneaten feed collection at the start of the experiment and through all the experiment period after 7d. To minimize nutrient leaching in faeces, only fresh and intact faeces were collected. Faeces were dried at 70 degrees C for digestibility determination. At the end of the trial, the fish were starved for Id and batch weighed. Fish were killed by a blow on the head and blood samples were collected (24h after last feeding) from the caudal vein of six fish from each tank at the end of the feeding trial by using heparinized syringes. Blood was centrifuged at 3500 r/min for 15 min, plasma-separated and stored at -80 degrees C. The remaining fish in each tank were taken for final fish body composition analysis. The results showed that feeding rate (FR), specific growth rate (SGR), feed conversion efficiency (FCE), protein retention efficiency (PRE) and energy retention efficiency ( ERE) decreased significantly (p < 0.05). Apparent digestibility coefficient of protein (ADCp) significantly increased (p < 0.05), but ADC of dry matter and energy decreased (p < 0. 05). Total nitrogen intake (TNI), apparent nitrogen intake ( ANI), faecal nitrogen Output (FNO), non-faecal nitrogen excretion (NFE) and nitrogen retention (NE) significantly decreased with the increasing dietary soybean meal (p < 0.05, but nitrogen load (NL) significantly increased (p < 0.05). Levels of plasma glucose, triacylglycerol and superoxide dismutase activities increased significantly with the increasing dietary, soybean meal (p < 0.05), but plasma cholesterol concentration and lysozyme activities decreased (p < 0.05). In conclusion, the results from this study showed adverse effects of inclusion of the soybean meal in diets on growth performance, feed utilization, nitrogen metabolism and immunity in gibel carp. The palatability was not negatively affected when soybean meal was included in the diets.Unbalanced amino acid composition of soybean meal diets seem to be the main reason to influence growth performance and nitroge load of gibel carp.