Effect of Supplemental Dietary -linolenic Acid (18:3n-3) on the Growth Performance, Body Composition, and Fatty Acid Profile of Coho Salmon (Oncorhynchus kisutch) Alevins Cultured in Freshwater

The present study evaluated the effects of supplemental dietary alpha-linolenic acid (ALA, 18:3n-3) on growth performance, body composition, hepatic fat metabolizing enzymes, and fatty acid profiles of coho salmon (Oncorhynchus kisutch) alevins cultured in freshwater. Six isonitrogenous and isolipidic experimental diets were formulated to attain different levels of ALA (0.09, 0.41, 0.76, 1.03, 1.32, and 1.68% dry weight) by adding linseed oil in a basal diet, respectively. Each diet was fed to triplicate groups of alevins (50 fish in each tank) with initial mean body weight of 0.352 & PLUSMN; 0.002 g. Fish were reared in a freshwater flow-through rearing system and fed to apparent satiation 4 times daily for 12 weeks. The specific growth rate (SGR) increased with increasing dietary ALA level, which reached the peak at 1.03% ALA group (p < 0.05). The final body weight (FBW) and SGR showed linear, quadratic, and cubic responses with the dietary ALA level. The whole-body crude protein increased with increasing dietary ALA level while lipid content was the opposite trend (p < 0.05). However, the content of crude lipid in the whole-body of fish showed quadratic and cubic responses with the dietary ALA level. In addition, except for fatty acid synthase (FAS), the hepatic enzymes activities of lipoprotein lipase (LPL), hepatic lipase (HL), and malate dehydrogenase (MDH) showed linear, quadratic, and cubic response with the dietary ALA level (p < 0.05) The activities of hepatic LPL and HL in 1.32% ALA group were significantly higher than other groups (p < 0.05). The activities of hepatic MDH and FAS in 1.32% ALA group were the lowest, which were significantly lower than those in ALA groups (form 0.09% to1.03%) (p < 0.05). Except for the content of MUFA, the contents of other fatty acids showed linear, quadratic, and cubic response with the dietary ALA level. The ALA and n-ary sumation n-3 PUFA content significantly increased with increasing dietary ALA levels (p < 0.05). These results indicated that dietary ALA actively impacted fish growth performance, hepatic lipid metabolizing enzymes, and muscle fatty acid profile. The cubic regression analysis based on SGR as evaluation indices indicated that the optimal dietary ALA content was 1.33% dry weight of diet for alevins.