Tannase alleviates the adverse physiological and toxicological impacts of supplementing tannin in the diet of grass carp (Ctenopharyngodon idellus)

Plant protein is the main substitution protein for fishmeal, especially rapeseed meal, and it contains anti-nutritional factors and toxicants such as tannin. Few studies have identified clear physiological or toxicological impacts of tannin on fish. Here, our experiment evaluated the physiological and toxicological effects of tannin on grass carp (Ctenopharyngodon idellus). Different concentrations of dietary tannin (1.5, 7.2, 19.9, 39.4, 83.2 and 162.0 g kg(-1) diet) were tested. Dietary tannin (>= 7.2 g kg(-1) diet) inhibited feed intake, and the appetite-promoting gene expression (Grehlin, NPY, Y8a and Y8b), meanwhile, increased the appetite-inhibiting gene expression (CCK and CART). Moreover, tannin addition reduced feed utilization (dietary nutrient retention, fat depot, activity of protease, lipase and amylase) of grass carp (p < .05). Besides, high dietary tannin (>= 39.4 g kg(-1) diet) lowered immunity (serum superoxide dismutase and catalase activities and the contents of total protein, albumin, complement component C3 and C4) (p < .05) and damaged the hepatic structure of grass carp, leading to attenuated growth in grass carp. This suggests that grass carp could not tolerate dietary tannin of >19.9 g kg(-1). The second trial designed to test the alleviation the negative effect of tannin by tannase. After adding tannase with a dose of 1000 or 1500 U kg(-1) to the diets, the weight gain of grass carp fed those diets was significantly increased compared with those fed the tannin and rapeseed meal addition groups (p < .05). Also, when high-level tannase was supplemented to the control diet, weight gain significantly improved. The decrease in feed intake by high dietary tannin and rapeseed meal was relieved through adding tannase in diet of grass carp, especially when tannase supplemented level reached 1000 U kg(-1) diet (p < .05). This study indicates that dietary tannin (>= 7.2 g kg(-1) diet) negatively affects the growth of grass carp through changing feed intake, feed utilization, immunity and hepatic structure, and addition of tannase reached 1000 U kg(-1) diet almost alleviate adverse effects of tannin and rapeseed meal (which included high contents of tannin) on grass carp.

Automated summary

High levels of dietary tannin (>= 7.2 g kg(-1) diet) negatively impact the growth of grass carp by affecting feed intake, feed utilization, immunity, and hepatic structure. The addition of 1000 U/kg dietary tannase almost alleviates the adverse effects of tannin and high-tannin rapeseed meal on grass carp.