低磷饲料中补充柠檬酸对大口黑鲈生长和营养物质利用率的影响

为了探究饲料中添加柠檬酸对大口黑鲈（Micropterus salmoides）生长、营养物质利用和氮（N）、磷（P）排放的影响，分别配制磷酸二氢钙（MCP）添加量为5、10（低磷饲料）、15 g/kg （对照饲料）的3组饲料（P5，P10，P15），在低磷饲料P5和P10中分别添加10 g/kg的柠檬酸，共5组实验饲料。投喂初始体质量为（16.0±0.16） g的大口黑鲈60 d。结果显示，随着MCP添加量的增加，大口黑鲈增重率、全鱼磷含量、粗蛋白沉积率、磷消化率、椎骨磷和血浆磷含量均显著增加（P<0.05），N排放量和全鱼粗脂肪含量显著下降（P<0.05），且均在P15组达到最佳水平。在P5饲料中添加柠檬酸，显著提高了鱼体增重率（+5.6%）和血浆磷含量，降低了饲料系数（-0.05）和N排放量（P<0.05），达到了和P10组基本一致的水平（P>0.05）；在P10饲料中添加柠檬酸，在数值上改善了生长性能（P>0.05），达到了和P15组基本一致的水平（P>0.05）。此外，在P5和P10饲料中补充柠檬酸，均显著提高了磷消化率，降低了P排放量（P<0.05）。综上所述，在低磷饲料中添加10 g/kg的柠檬酸可改善大口黑鲈生长、提高饲料和磷的利用率。

Effects of citric acid supplementation in low phosphorus diets on growth and nutrient utilization of largemouth bass (Micropterus salmoides)

The effects of citric acid supplementation in diets were evaluated on the growth, nutrient utilization, and nitrogen (N) and phosphorus (P) secretion of largemouth bass (Micropterus salmoides). Three diets were prepared with the addition of monocalcium phosphate (MCP) at 5, 10 (low-P diets), and 15 g/kg (positive control) (P5, P10, P15), then 10 g/kg of citric acid was added into the two low-P diets of P5 and P10. The five diets were fed to juvenile fishinitial body weight (16.0 ±0.16) g] for 60 days. The results showed that the weight gain (WG), whole body P, crude protein retention, P digestibility, vertebral P and plasma P significantly increased, and N excretion, whole body crude lipid decreased with the increasing MCP level (P<0.05); P15 group showed the best performance among all the groups. The addition of citric acid in P5 diet significantly increased WG (+5.6%) and serum P level, and reduced FCR (-0.05) and N excretion (P<0.05), which reached the similar levels to the P10 group (P>0.05). The addition of citric acid in P10 diet numerically improved the growth performance with similar levels to the P15 group (P>0.05). The supplementation of citric acid in both P5 and P10 diets significantly promoted P digestibility and reduced P excretion (P<0.05). In summary, the addition in 10 g/kg citric acid in low-P diets can improve the growth and the utilization of P and diet in largemouth bass.