| dc.description.abstract | This work was carried out to evaluate the performance and carcass characteristics of grass carp (Ctenopharyngodon idella) juveniles in response to dietary protein levels and sources. For this, two experiments were conducted: the first (80 days), evaluating four crude protein (CP) levels (22, 30, 36 and 44%) and the second (60 days), comparing protein sources in the diet: FCS (porcine meat meal -
control); FC: canola meal; FG: sunflower meal and FCG: canola meal + sunflower meal. Both experiments were conducted in a water re-use system composed of 12 tanks (850 L), with three replicates per treatment. In experiment 1, 10 fish by tank (initial weight 153,0±1,5g) were fed 3% of body weight, twice daily, and the experiment 2 was provided ration (2% of biomass) in the morning and forage (Napier grass ad libitum) in the afternoon, to 15 fish by tank (initial weight 54,6±1,0g).
Growth parameters (weight, specific growth rate, daily weight gain, relative weight gain and feed conversion ratio) and carcass (carcass and fillet yield, digestive somatic index, hepatic somatic index and visceral fat index, intestinal quotient, protein retention, protein efficiency rate and whole body and fillet protein and fat deposition) were evaluated. Moreover, the proximate composition (moisture, ash, fat and protein) in fillet and whole fish and blood parameters (glucose, total triglycerides, total cholesterol and total protein in both experiments and hematocrit in Experiment 1) were also evaluated. In experiment 2 was also determined the daily consumption of forage and the instrumental color. In
experiment 1, linear positive effect of protein level for all growth variables was observed. However, the same effect was observed to whole body and fillet fat deposition, triglycerides and total cholesterol
in serum, indicating that the protein from the diet was used as energy source. To feed conversion ratio
and fat in whole fish, the effect was quadratic, with maximum response with 40.6 and 37.1% CP, respectively. Protein retention, protein efficiency ratio, protein deposition in whole body and fillet and hematocrit also showed linear positive effect, while the other parameters were not affected. In experiment 2, the growth parameters and the daily consumption of forage (1.24 to 2.11% of body
weight) did not differ among the treatments. About proximate composition of whole fish, higher fat content and lower protein content, besides fillet ash, were obtained in the treatment FCG. The diet FCS presented the highest values of serum protein, triglycerides and total cholesterol. The fillet yield was higher in the treatments FCG and FC, while the digestive somatic index was higher in treatment FG and FCG. In the instrumental evaluation of color, the fillets from FCS and FCG diets showed higher value of L (brightness), differing only treatment FC. The other parameters did not differ among them. Based on this results, we can conclude that: the minimum protein level for maximum growth of grass carp in the growing phase, with practical diets, is 44%; the variation in dietary protein level promotes changes in metabolism of juvenile grass carp, reflected in hematological and carcass
parameters; canola meal and sunflower meal can be used in diets for grass carp growing phase, when supplemented with limiting essential amino acids, without compromising growth. | |
