Effects of sorbic acid supplementation in low phosphorus diety on growth, intestinal health and phosphorus metabolism of Songpu mirror carp (Cyprinus carpio Songpu)

This study aimed to explore how sorbic acid supplementation in low-phosphorus feed affects the growth, intestinal health, and phosphorus absorption of juvenile Songpu mirror carp (Cyprinus carpio Songpu). Juvenile C. carpio Songpu with an initial body weight of (5.07±0.02) g were fed for 8 weeks. Five experimental diets were formulated: monosodium dihydrogen phosphate was used as the phosphorus source, the phosphorus supplementation level was set at 2% for the control group (C); for the experimental groups, the phosphorus supplementation level was fixed at 1.5%, namely 0% (S0), 0.5% (S0.5), 1% (S1) and 2% (S2). The results showed that: Compared with the S0 group, the final body weight, weight gain rate (WGR), crude protein and crude ash contents in the whole fish of the S1 group were significantly increased, while the feed conversion ratio (FCR) and crude lipid content in the whole fish were significantly decreased. Moreover, all these indices showed no significant difference from those of the C group. The S1 group showed a marked increase in serum phosphorus concentration relative to the C and S0 groups. In contrast, serum urea nitrogen (BUN) concentrations were significantly reduced in the S0.5, S1, and S2 groups compared to the C and S0 groups. After sorbic acid supplementation, the trypsin activities in the foregut of the S1 and S2 group, as well as in the midgut and hindgut of all sorbic acid-supplemented groups, were significantly higher than those in the S0 group, with no significant differences from the C group. In the S1 group, the total antioxidant capacity (T-AOC) in all intestinal segments, as well as superoxide dismutase (SOD) and reduced glutathione (GSH) in the midgut, were significantly higher than those in the C and S0 group. Additionally, catalase (CAT) activities in the foregut and midgut of the S1 group were significantly higher than those in the S0 group and showed no significant difference from the C group. Compared with the S0 group, the fold heights of the foregut in all sorbic acid supplemented groups, as well as those of the hindgut in the S1 and S2 groups, were significantly increased and did not differ from those of the C group. The villus width in the hindgut of the S1 group was not significantly different from that of the C group but was significantly higher than that of other low-phosphorus groups. The muscular thickness in the S1 group was significantly higher than that in the S0 group but showed no significant difference compared to the C group. The expression levels of type IIb sodium-dependent phosphate transporter (NaPi-Ⅱb) in the foregut of all sorbic acid-supplemented groups were significantly lower than those in the S0 group.; the expression level of NaPi-Ⅱb in the hindgut of the S0.5 and S1 groups was significantly lower than that in the S0 group. The expression level of sodium-potassium-dependent ATPase (Na⁺-K⁺-ATP) in the foregut of sorbic acid-supplemented groups showed no significant difference from that in the C group. The expression level of AKP in the S2 group was significantly higher than that in all other group. In conclusion, dietary supplementation of 1% sorbic acid in low-phosphorus diets can regulate digestive enzyme activities, improve intestinal health, promote phosphorus absorption, and ultimately enhance the growth performance of C. carpio Songpu .