Effects of highly unsaturated fatty acids on escape ability from moon jellyfish Aurelia aurita in red sea bream Pagrus major larvae

The development of escape behavior from moon jellyfish Aurelia aurita was studied in the red sea bream Pagrus major larvae raised with two distinct dietary regimes: one fed rotifers and Artemia nauplii enriched with highly unsaturated fatty acids (the HUFA-enriched group); and the other fed those without enrichment (the HUFA-deficient group). The length of time that it took for a larva to be captured by three medusae of A. aurita was measured. The observation was continued for 5 min. The capture time was compared between the two dietary groups for the same age, and among different ages within the same dietary group. The capture time in the HUFA-enriched group was significantly longer on day 18 and day 20 compared to the younger stages, whereas there was no such discernible developmental changes in the HUFA-deficient group. The average capture time on day 18 in the HUFA-enriched and HUFA-deficient groups was 277 and 161 s, respectively, with almost the same body length (7.1 mm and 7.2 mm, respectively). Fatty acid analysis revealed that rotifers and Artemia in the HUFA-enriched group contained 2.2 and 0.6% of docosahexaenoic acid (DNA) in dry weight, whereas those in the HUFA-deficient group did not contain any detectable amount of DHA. Present work revealed that A. aurita can be a potential predator of P. major up to lengths of 7.1 mm (day 18) when the nutritional condition of the fish was good, and that the threat can be serious up to larger sizes when the fish had experienced inferior dietary conditions.