Effects of dietary citric acid on growth performance, mineral status and intestinal digestive enzyme activities of large yellow croaker Larimichthys crocea (Richardson, 1846) fed high plant protein diets

The positive effects of citric acid (CA) on aquaculture species have been reported. However, extensive application of CA needs a comprehensive understanding of its nutritional functions. A 9-week feeding trial was conducted to determine the effect of dietary CA on growth performance, tissue mineral content, intestinal enzyme activities and oxidative status of large yellow croaker Larimichthys crocea fed high plant protein diets. Six isonitrogenous and isolipidic diets were formulated and fed to triplicated groups of fish. A high fish meal diet formulated with 45% fish meal and 11.5% soybean meal was set as the positive control diet, while a high plant protein diet formulated with 31.50% fish meal and 30.63% soybean meal was used as the negative control diet. The other four diets were supplemented with 0.4%, 0.8%, 1.6% and 3.0% of CA into the negative control diet, respectively. The results showed that the specific growth rate, feed efficiency, protein and phosphorus retention, phosphorus and zinc concentrations in whole body and intestine, activities of the leucine-aminopeptidase, alkaline phosphatase and Na+, K+-ATPase were significantly reduced after soybean meal replacement and recovered by dietary CA supplementation (P<0.05). Data on oxidative stress and anti-oxidative responses of intestine showed that the content of malondialdehyde was significantly increased in soybean meal-enhanced diets, which decreased with supplementation of CA varying from 0.4% to 1.6% (P<0.05). The total anti-oxidative capacity, activities of total superoxide dismutase and Cu–Zn superoxide dismutase were decreased by soybean meal replacement and increased as CA level increasing from 0.4% to 0.8% (P<0.05). In conclusion, 0.8–1.6% of CA in diet is helpful for large yellow croaker fed high plant protein diets to get better growth performance. The improvement of growth performance could be partly due to the increased mineral bioavailability, enhanced intestinal antioxidant capacity and recovered intestinal function by dietary CA supplementation.