Feed intake, feed utilization and feeding-related gene expression response to dietary phytic acid for juvenile grass carp (Ctenopharyngodon idellus)

The negative effect of dietary phytic acid (PA) in feed intake is a common feature of response to stress in fish, but the regulation mechanism of feed intake is poorly understood. Our study was therefore conducted to estimate the effects of dietary PA on feed intake, feed utilization and feeding-related gene expression in juvenile grass carp. The levels of dietary PA supplementation were 0 (control), 5 (low) and 40 (high) g kg− 1 diet, respectively. Triplicate groups (nine 300-L tanks) of grass carp (mean weight, 22.37 ± 0.16 g) were fed twice daily (08:00 and 16:00 h) to satiation for 8 weeks. Supplemental PA decreased the weight gain, feed intake, feed utilization and digestive enzyme activities of grass carp. Dietary PA supplementation decreased the apparent digestibilities of phosphorus, calcium and crude protein. The gene expression levels of cocaine- and amphetamine-regulated transcript (CART) and cholecystokinin (CCK) in the brain were enhanced with the increase of dietary PA supplementation. However, the neuropeptide Y (NPY) and ghrelin mRNA expression levels were reduced in fish fed with low PA, but increased significantly (P < 0.05) in fish fed with high PA compared to the control. No significant differences were observed in the gene expressions of NPY receptors Y8a and Y8b among all the groups. The results of this study indicated that the decrease of feed utilization and the increase of CART and CCK gene expressions in the brain might be the main factors for the decrease of feed intake in grass carp caused by dietary PA supplementation.