Association between a diamondfish and box jellyfish during an encounter with a carcharhinid shark

Fish-cubomedusa associations are less frequently reported than those involving scyphozoans and are typically limited to larval or juvenile fishes without an explicit predator context. Here, we report an adult Monodactylus argenteus associated with the cubozoan Morbakka sp. during an encounter with a carcharhinid shark at Magnetic Island, Australia. Throughout the observation, the fish maintained close association with the cubomedusa and reduced its distance to the bell and upper tentacle field during the shark encounter. Although behavioural motivations could not be determined from aerial observations alone, the observed change in spatial positioning by the fish was consistent with refuge use. This observation extends previous reports of fish-cubomedusa associations by documenting such an interaction in an adult fish during an encounter with a carcharhinid shark.