Effect of dietary linolenic acid/linoleic acid ratio on growth performance, hepatic fatty acid profiles and intermediary metabolism of juvenile yellow catfish Pelteobagrus fulvidraco

The present study aimed to evaluate the effect of dietary linolenic acid (LNA)/linoleic acid (LA) ratio on growth performance, hepatic fatty acid profile and intermediary metabolism of juvenile yellow catfish Pelteobagrus fulvidraco. Six isonitrogenous and isolipidic diets were formulated to contain incremental levels of LNA from 0 to 5% at the expense of corn oil (rich in LA), resulting in six dietary treatments with LNA to LA ratios ranging from 0.35 to 14.64. The experiment continued for 7 weeks. Best growth and feed intake were obtained in the fish fed the diets containing the LNA/LA ratios of 1.17 and 2.12 (P < 0.05). In contrast, feed conversion ratio was the lowest for fish fed the diets containing the LNA/LA ratios of 1.17 and 2.12 (P < 0.05). Dietary LNA to LA ratios significantly influenced viscerosomatic index and hepatosomatic index (P < 0.05), but not condition factor (P > 0.05). Body composition was also significantly influenced by dietary LNA to LA ratios (P < 0.05). Generally, liver FA compositions reflected dietary FA profiles. Declining LA and increasing LNA contents in liver were observed with the increasing dietary LNA/LA ratios (P < 0.05). Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) increased with the increasing LNA to LA ratios, suggesting that yellow catfish could elongate and desaturate C18 polyunsaturated fatty acids into highly unsaturated fatty acids . As a consequence, the n−6 fatty acids (FA) declined, and total n−3 FA and n−3/n−6 ratios increased with the dietary ratios of LNA/LA (P < 0.05). Dietary LNA to LA ratios significantly influenced several enzymatic activities involved in liver intermediary metabolism (P < 0.05), such as lipoprotein lipase, hepatic lipase, pyruvate kinase, succinate dehydrogenase, malic dehydrogenase and lactate dehydrogenase, suggesting that dietary LNA/LA ratios had significant effects on nutrient metabolism in the liver. To our knowledge this is the first demonstration of the effects of dietary LNA to LA ratios on the enzymatic activities of liver in fish, which provides information on diet quality and utilization, and can also be used as an indicator of the nutritional status of this fish.