Effects of dietary n-3/n-6 ratio on lipid metabolism of gilthead seabream (Sparus aurata)

The current study was conducted to evaluate the effects of various dietary n-3/n-6 ratio on growth and lipid metabolism in gilthead seabream (Sparus aurata) juveniles. The fish were fed ad libitum on three isoproteic (52%), isolipidic (14%), and isoenergetic diets (21 MJ/kg), formulated to contain three different n-3/n-6 ratios: a high (3.8), medium (2.5), or low (0.9) ratio. Fish grew from 9.5 +/- 0.1 g to 54.2 +/- 0.7 g in 12 weeks. Growth rate (2.2% BW/day), voluntary feed intake (2.4 +/- 0.1% BM/day), feed conversion ratio (1.38 +/- 0.05), and net protein utilization (27.5 +/- 1.0%) did not vary among treatments. In contrast, body lipid content and lipid deposition efficiency were significantly reduced in fish fed low n-3/n-6 ratio. Fish fed the highest n-3/n-6 ratio showed the lowest hepatic glucose-6-phosphate dehydrogenase (G6PD) activity (p = 0.02). The n-3/n-6 ratio decreased, while DHA/eicosapentaenoic acid (EPA) ratio increased significantly with decreasing dietary n-3/n-6 content. Among n-3 PUFA, the DHA and, particularly, the docosapentaenoic acid (DPA) showed the highest deposition rate both in muscle and liver. The lower deposition rate (<1) of linoleic acid (LA) and linolenic acid (LNA) suggests that a reduction in dietary n-3/n-6 ratio may stimulate their transport to the intermediary metabolism for energy production.