Feeding moon jellyfish improves the tilting behavior of hatchery-reared red sea bream juveniles

We evaluated the efficiency of feeding moon jellyfish Aurelia sp. to red sea bream Pagrus major by conducting nutritional and behavioral analyses. Four treatments were prepared in our 108-day feeding trial as follows: starved (S), fed only jellyfish (J), fed only pellets (P), and fed both jellyfish and pellets (JP). Juveniles consumed jellyfish as much as 5.3 and 1.3 times their own body weight per day in the J and JP treatments, respectively. Although there were no major contributions to the growth by feeding jellyfish, fish in the J treatment showed better survival, daily growth rate or condition factor than those in the S treatment. Fish in the JP treatments showed a significantly higher rate of exhibiting tilting (anti-predator) behavior than those in the P treatment. The latency to start tilting after the transference was significantly shorter, whereas the latency to start swimming was significant longer in the JP treatment than in the P treatment. We recommend the utilization of jellyfish as subsidiary prey for juvenile fish for stock enhancement.