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Comparison between α-LNA and DHA in early developmental stages of Takifugu obscurus and Takifugu rubripes

Rearing experiments were conducted to investigate the essential fatty acid requirements in the early developmental stages of river puffer Takifugu obscurus and tiger puffer T. rubripes using two n−3 series unsaturated fatty acids, α-linolenic acid (18∶3n−3, α-LNA) and docosahexaenoic acid (22∶6n−3, DHA), under salinity of 30 and 18.5–20.3°C. River and tiger puffer larvae used in this study were 15 and 14 days old after hatching, and their average body weights were 30.1 and 20.8 mg, respectively. The results on fatty acid requirements of these two species were evaluated from fish growth, survival, fatty acid composition of the fish body and activity test results. The DHA groups of both river and tiger puffer exhibited better survival and weight gain. However, there was no difference in the mean final body weights of river puffer between two dietary groups. Also, the DHA group of tiger puffer showed better results in the recovery test from anesthetic condition than that obtained in the LNA group. In an examination of the fatty acid compositions of the whole body, the LNA group containing no dietary DHA resulted in 0.5% DHA in tiger puffer and 1.1% DHA in river puffer. These results suggest that α-LNA from Artemia converted to eicosapentaenoic acid (20∶5n−3, EPA) and to DHA successively by their fatty acid metabolism. Symptoms following essential fatty acid deficiency were not observed in any experimental groups. As river puffer did not represent a significant difference in the dietary effects between α-LNA and DHA treatment groups, its essential fatty acid requirement was assumed to be somewhat closer to that of the freshwater fishes in comparison with that of marine fishes, including tiger puffer.