Estimation of the Optimum Dietary Protein to Lipid Ratio in Juvenile Pengze Crucian Carp (Carassius auratus Var. Pengze)

Abstract

An 8-week feeding experiment was conducted to evaluate the effect of dietary protein to lipid ratio on fish growth performance, digestive enzyme activity, body composition, serum biochemistry, immunity, and antioxidant capacity of Carassius auratus var. Pengze juveniles. Nine experimental diets were formulated in a $3\times 3$ factorial design to contain three protein levels (30%, 35%, and 40%) and three lipid levels (5%, 8%, and 11%), with protein-to-energy (P/E) ratios ranging 19.2–27.1 mg/kJ and named as Diet 1 (30/5), Diet 2 (30/8), Diet 3 (30/11), Diet 4 (35/5), Diet 5 (35/8), Diet 6 (35/11), Diet 7 (40/5), Diet 8 (40/8), and Diet 9 (40/11), respectively. Each diet was randomly assigned to triplicate groups of 20 fish per cylindrical fiberglass tank. The fish fed with Diet 4 had the highest specific growth rate (SGR) among the 9 groups. The whole-body lipid content increased significantly with increasing dietary lipid levels regardless of dietary protein content ( $P<0.05$ ), whereas moisture content showed an opposite trend ( $P<0.05$ ). The highest values of activities of serum lysozyme (LZM) and alkaline phosphatase (AKP) were detected in the fish fed Diet 4 (35/5), whereas malondialdehyde (MDA) was lowest in the fish fed Diet 4. In addition, serum total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) were the lowest, while high-density lipoprotein (HDL-C) and high-density lipoprotein to total cholesterol ratio (HDL-C/TC) were the highest in the Diet 4 group. The results indicate that a combination of 35.1% protein and 5.1% lipid with dietary CP/GE (mg/kJ) ratio of 24.0 is optimal for the culture of Carassius auratus var. Pengze juveniles.