Ontogenetic changes in the predator–prey interactions between threadsail filefish and moon jellyfish

Although jellyfish are important predators of fish larvae, many fish species also feed on jellyfish. Therefore, the predator–prey role of jellyfish and fish may switch during the course of their life histories. Here, we investigated such interactions by examining (1) the avoidance behaviour of threadsail filefish Stephanolepis cirrhifer to moon jellyfish Aurelia sp. and (2) the feeding behaviour of filefish on moon jellyfish medusae and polyps. The efficiency of filefish as jellyfish predators was examined by comparing their behaviour with that of black scraper Thamnaconus modestus and red sea bream Pagrus major . Filefish and black scraper were able to avoid medusae and obtain tolerance against nematocysts at a smaller body size compared to red sea bream. Filefish initiated feeding on medusae when they became juveniles of 21.8 mm SL. Feeding trials of yearling filefish on polyps at different temperatures (range 10–30°C) indicated that the highest feeding rate was 3.1 individuals s −1 at 26.8°C. We suggest that the feeding pressure of filefish on jellyfish polyps may have an impact on medusa biomass.