Effects of a-ketoglutarate (AKG) supplementation in low phosphorous diets on the growth, phosphorus metabolism and skeletal development of juvenile mirror carp (Cyprinus carpio)

Abstract

The a-ketoglutarate has a positive effects on phosphorus metabolism and bone synthesis and is expected to decrease the phosphorus requirement of fish, so as to reduce phosphorus pollution in aquaculture. The effects of AKG supplementation in low phosphorous (P) diets on the growth, P metabolism and skeletal development of juvenile songpu mirror carp (Cyprinus carpio) were studied. Triplicate groups of mirror carp (6.67 ± 0.08 g) were fed diets containing a total phosphorous of 0.96% (adequate P, AP) and 0.82% (low P, LP), with graded levels 0 (LP-0), 0.2% (LP-0.2), 0.4% (LP-0.4), 0.6% (LP-0.6), 0.8% (LP-0.8) and 1.0% (LP-1.0) of AKG added to diets; fish were fed to satiation for 8 weeks. The results are as follows: Compared with the AP group, the weight gain rate (WGR) and the specific growth rate (SGR) were significantly lower and the feed coefficient rate (FCR) was significantly higher (P < 0.05); the content of crude lipid (EE) was significantly higher; the contents of Ca and P of the vertebra were significantly decreased (P < 0.05); and the activity of alkaline phosphatase (ALP) in plasma were significantly decreased in the LP-0 group (P < 0.05). Compared with the LP-0 group, the WGR, SGR, PER, HI, CF, content of P in the vertebra and P deposition rate (PDR)were significantly increased; the FCR was significantly decreased in the LP-0.6 group (P < 0.05); the ALP was significantly increased in the AKG supplementation groups (P < 0.05); and the content of collagen in the vertebra was significantly increased with the 0.6–1.0% AKG supplementation (P < 0.05). The expression of NaPi-IIb mRNA in the foregut, midgut and hindgut, kidney and vertebra were similar between the AP and LP-0 groups (P > 0.05), but the expression of NaPi-IIb mRNA in the foregut and hindgut were significantly decreased in the AKG supplementation group (P < 0.05); and the IGF-I mRNA significantly increased by 0.4–1.0% in the AKG supplementation groups (P < 0.05). This study confirmed that the supplementation of AKG can promote growth performance, P metabolism, and the synthesis of collagen in vertebra.