Beneficial effects of re-feeding high α-linolenic acid diets on the muscle quality, cold temperature and disease resistance of tilapia.

To investigate the effects of re-feeding high α-linolenic acid (ALA) diets on the muscle quality, cold temperature and disease resistance of the tilapia with nutritional history of soybean oil diets, three experimental diets with linoleic aicd (LA)/ALA ratios at 9 (D1, taking soybean oil as lipid sources), 3 and 1 (D2 and D3, taking soybean and linseed oils as lipid sources) were prepared to re-feed juveniles for 10 weeks, and the growth performance, muscle quality were analyzed. After the re-feeding trial, the fish were fasted for 8 weeks at cold temperature (15°C-20 °C) and then subjected to the Aeromonas hydrophila challenge, and the cold temperature and disease resistance of the fish were evaluated. It was shown that a comparable growth performance was detected among the three dietary groups, while, the high feed efficiency and low viscerosomatic and hepatosomatic index were detected in the D2 and D3 groups compared with the D1 group. In addition, the docosahexaenoic acid (DHA) and n-3 polyunsaturated fatty acid (PUFA) levels of the muscle increased in a parallel pattern with the dietary ALA levels, and the muscular tenderness, adhesiveness, and chewiness were modified substantially in fish fed the diets D2 and D3. After 8-week fasting at cold temperature, the low serum total antioxidant capacity (T-AOC) and malondialdehyde (MDA) levels, and high serum lysozyme (LZM) and C3 levels were observed in the D2 and D3 groups compared with the D1 group. It was also shown that high eicosapentaenoic acid (EPA), DHA, and n-3 PUFA levels were observed in the intestine, liver, and spleen of fish from D2 and D3 groups. Correspondingly, in the fish of the D2 and D3 groups, the mRNA levels of lzm in the liver, intestine, and spleen, and c3 in the intestine and spleen were increased, while the mRNA levels of il-1β, ifn-γ, and tnf-α in the intestine, and ifn-γ, tnf-α in the liver, as well as spleen il-1β, were decreased. Furthermore, the survival at day 15 post-challenge of A. hydrophila in the D2 and D3 groups were higher than those of the D1 group. The results demonstrated that re-feeding high ALA diets were beneficial to the muscle quality, cold temperature and disease resistance in the tilapia, and provide a basis for selecting the dietary lipid sources of tilapia pre-winter feed.