Effects of dietary zinc (Zn) levels on growth performance, nutrient composition, muscle development, antioxidant and inflammatory responses in yellow catfish muscle

Three diets were formulated with dietary zinc (Zn) levels at 12.10 mg Zn/kg (L-Zn), 18.69 mg Zn/kg (M-Zn) and 120.82 mg Zn/kg (H-Zn) to explore effects of dietary Zn on growth, nutrient composition, muscle development, antioxidant and inflammatory responses in the muscle tissues of yellow catfish, one of the important economic fish in several Asian countries, including China. Zn content in M-Zn group could meet Zn requirement of yellow catfish. 270 juvenile yellow catfish (4.97 ± 0.01 g, mean ± S.E.M) were stocked in nine 300-L indoors tanks, 30 yellow catfish in each tank, and randomly provided with three diets for 10 weeks. Among three treatments, yellow catfish fed the middle Zn diets showed higher growth performance and condition factor but lower feed conversion rate than those fed the high Zn diets. Dietary Zn addition increased muscle Zn contents, but did not significantly influence feed intake, viscerosomatic and hepatosomatic index, survival, moisture, lipid, crude protein and ash contents in the muscle. Dietary Zn levels significantly influenced mRNA expression of several muscle development-related genes, such as mef2a, myod, myf5, myog, mef2d, pax7, mrf4, myhcand mstn. Middle dietary Zn levels increased antioxidant capability and reduced oxidative stress, as evaluated by enzymatic activities, gene and protein expression related to antioxidant response. Fish fed the middle Zn diets had the lower il8, tnf-αand tnf-βmRNA expression but higher il10and tgf-βmRNA expression than those fed the high Zn diet, suggesting that optimal dietary Zn levels activated anti-inflammatory response and inhibited pro-inflammatory responses. Based on the observation, our study suggested that the suitable dietary Zn levels promoted the growth, muscle development, antioxidant and anti-inflammatory responses in fish.