Juvenile Rudderfish Reportedly Accompany Giant Phantom Jellyfish Off Argentina

About 19 young fish swimming beneath the giant jellyfish

ScienceAlert reports that researchers using an ROV in mesopelagic waters off Argentina observed about 19 juvenile rudderfish (Centrolophus niger) swimming beneath the bell and among the oral arms of a giant phantom jellyfish (Stygiomedusa gigantea). The jellyfish was described as about 6 meters long at a depth of around 250 meters.

In 1973, trawl catches in the North Atlantic led researchers to suggest that rudderfish and giant phantom jellyfish might associate, but they had not observed the pair alive together in their natural habitat.

The reported ROV encounter provides visual evidence of juvenile rudderfish associating with a giant phantom jellyfish in the deep ocean. The function of the association remains unresolved.

Possible refuge and uncertain benefits

The account is described as the first documented deep-ocean observation of this particular association. Researchers suggest the jellyfish may offer the young fish refuge, but they could not determine what the fish were eating or whether the jellyfish benefits.