Influences of different arachidonic acid levels and temperature on the growth performance, fatty acid profile, liver morphology and expression of lipid genes in cobia (Rachycentron canadum) juveniles

Abstract

An 8-week nutritional experiment was conducted with the aim of evaluating the influences of different arachidonic acid (ARA) levels and two different temperatures (29.5 °C and 26.5 °C) on the growth performance, tissue and whole-body fatty acid (FA) compositions, plasma prostaglandin concentration, liver morphology and expression of genes related to lipid metabolism in cobia juveniles. A basal fat-reduced diet was manufactured and subsequently coated with different FA sources, distinct levels of ARA (ARA1, 0.5%; ARA2, 1.2%; and ARA3, 1.9%) and fish oil (FO: 8.8%, as a control diet). All diets were formulated to be isoproteic and isolipidic. Cobia juveniles (5.86 ± 0.40 g) were randomly divided into 24 tanks with 18 animals each. Twelve tanks were kept at 29.5 °C, and 12 tanks were kept at 26.5 °C. The animals were fed twice per day with each experimental diet until apparent satiation in triplicate tanks at both temperatures. The results revealed that the animals maintained at 26.5 °C and fed with the ARA diets exhibited better growth than those fed with the FO diet and kept at 29.5 °C. In contrast to observations in other teleost species, ARA excess did not reduce growth or survival. The FA compositions of the livers, fillets and whole bodies generally reflected the diet compositions, i.e., gradual increases in ARA were observed according to the diet level. Additionally, greater depositions of docosahexaenoic acid (DHA) in the fillets of the animals from the ARA2 group that was kept at 26.5 °C were observed. The plasma prostaglandin levels were greater in the animals that were kept at 29.5 °C for all experimental diets and in the ARA2 animals compared with the FO groups at both temperatures. The FAS and SREBP-1 expressions in the livers were down-regulated in the ARA1 and ARA2 animals that were maintained at 26.5 °C compared with the animals that were fed the same diets but kept at 29.5 °C. Additionally, SREBP-1 expression was up-regulated in the ARA2 animals compared with the FO animals at both temperatures. The results of this study indicated that ARA inclusion between 0.5 and 1.9% combined with a temperature of 26.5 °C can improve juvenile cobia growth performance and directly influence the modulation of prostaglandin synthesis and the relative expressions of lipid genes.