| Large yellow croaker Pseudosciaena crocea is one of the commerciallyimportant marine fish species in China. It is geographically distributed from thesouthern part of the Yellow Sea to the northern part of the Southern China Sea. Aseries of studies on nutrient requirements of this fish have been investigated. However,there are no published data on the dietary protein requirement of this species at thegrowth stages between fingerlings and the market size. It is one of the most importantconstraining factors on the precise feed formulation for this species. The aim of thisstudy is to determine the protein requirements of large yellow croaker at threedifferent growth stages and the optimum dietary protein to energy ratio of this fish.A9-week growth experiment is conducted to investigate the effects of dietaryprotein levels on growth performance, feed untiliztion, protein deposition, keyenzymes and metabolites related to protein metabolism of large yellow croakerPseudosciaena crocea at three different growth stages. There are three feeding trialswith three growth stages of large yellow croaker, respectively. The initial bodyweights are12.8±0.08g,137.9±0.81g and194.1±2.37g, respectively. These fishare denominated as small fish (SF), middle fish (MF) and large fish (LF), respectively.Seven isocaloric diets containing30%,34%,38%,42%,46%,50%and54%of crudeprotein are used in this study. Results shows that survival rate, hepatosomatic indexand viscerosomatic index are independent of dietary treatment at three growth stages(P>0.05). For fish in three growth stages, specific growth rate (SGR) and feedefficiency ratio (FER) increase with the increasing protein levels and then remainedconstant, but feed intake (FI) decreases. Protein efficiency ratio (PER) and proteinproductive value (PPV) have the similar change pattern with SGR. Body protein content (BP) and nitrogen retention rate (NR) significantly increase with the contentof protein in the diet in SF feeding trial (P<0.05), but there are no significantdifferences in MF and LF (P>0.05). From the growth stages point of view, NR in MFfeeding trial is significantly lower than those in SF and LF. The activity of hepaticaspartate aminotransferase (AST) and alanine aminotransferase (ALT) significantlyincrease with the increasing dietary protein levels in SF, MF and LF. Meanwhile, theconcentration of ammonia, urea and free amino acids in serum also rise with thedietary protein content in this three feeding trials. However, the concentration ofserum ammonia in MF is significantly higher than those in SF and LF. Broken-lineregression analysis shows that the optimum dietary protein requirements formaximum SGR for large yellow croaker at three growth stages (initial body weight12.8,137.9and194.1g) under these experimental conditions are48.3%,44.8%and42.7%, respectively.An8-week feeding trial experiment is conducted to evaluate the effect on dietaryprotein energy ratio for large yellow croaker (initial weight,137.9±0.81g) diets ongrowth performance, body composition and physiological indices. Determine theoptimum dietary protein to energy ratio for large yellow croaker think to be the bestgrowth performance among these groups. Results showes that specific growth rate(SGR) and feed efficiency ratio (FER) increase with the increasing protein levels andthen remained constant, but feed intake (FI) decreases. Protein efficiency ratio (PER)and protein productive value (PPV) have the similar change pattern with WGR andSGR. The activity of hepatic aspartate aminotransferase (AST) and alanineaminotransferase (ALT) significantly increase with the increasing dietary proteinlevels. Meanwhile, the concentration of ammonia, urea and free amino acids in serumalso rise with the dietary protein content. According to the results, the dietary proteinto energy ratio has a significant effect on growth performance. It indicates that theoptimum protein to energy ratio is29.78mg/kJ (protein:46%, lipid:12%). |
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