Effects of supplemental hydrolysable tannin on feeding preference, nutrition digestion and antioxidant ability of obscure puffer (Takifugu fasciatus)

Total 720 Takifugu fasciatus (initial weight 39.84 ± 3.09 g) were fed with four isonitrogenous and isoenergetic semi-purified diets for eight weeks: control diet (T0) with hydrolysable tannin-free protein sources (containing 43% fish meal) and three experimental diets supplemented with 0.25%, 0.75%, and 1.25% hydrolysable tannin (called T1, T2, and T3, respectively). In experimental diets, crude protein content was balanced by casein when fish meal level decreased, and the ratio of casein to tannin was nearly equal to that of protein content to tannin content in rapeseed meal (16.8:1).The results showed that the weight gain rate was not influenced, while feed coefficient ratio decreased significantly with increasing tannin level; the muscle crude lipid of T2 was significantly higher than those of T0 and T1, and the amino acid level of T0 was significantly higher than other groups ; for liver antioxidant index, the activity of catalase (CAT) in T0 was significantly lower than other groups, while total antioxidative capacity (T-AOC) in T0 was significantly higher than other groups, the activity of superoxide dismutase (SOD) and the content of malonaldehyde (MDA) in T3 was significantly higher than other groups; for serum antioxidant index, the activity of SOD showed no significantly difference (P>0.05), while the content of MDA in T0 was significantly lower than other groups, and the activity of catalase (CAT) decreased with increasing tannin level; for serum biochemical indices, the activity of ALT first increased, and then decreased at T2, paralleling the result of ALT in liver, the content of album (ALB) in T1 was higher than T3 (P>0.05) and T1 was significantly higher than T0 and T3 groups, the total protein (TP) content of T1 was higher than T0, and T1 was significantly higher than T2 and T3; the activity of intestinal amylase in T1 and T2 groups were significantly higher than T0 , the activity of protease increased with increasing tannin level in both stomach and intestine, the activity of lipase decreased in stomach; the expression of T2R1mRNA in T3 was significantly higher than T0 both in tongue and intestine(P<0.01); the expression of HSP70 mRNA in liver in T0 was significantly higher than T3 . Furthermore, the preference decreased with increasing tannin level before feeding test , while after 8-week domestication, the fish preferred to diet containing 0.75% tannin in all groups . In conclusion, feeding obscure puffer with diet containing no more than 1.25% supplemental hydrolysable tannin would not decrease growth and feed coefficient ratio, while it would change the digestion of protein, lipid, carbohydrate and anabolism of protein, and when the amount of supplemental hydrolysable tannin was up to 1.25%, antioxidant ability and anti-stress ability were both damaged.