A juvenile carangidae appears to be holding an anemone in its mouth. Credit: Linda Ianniello
Researchers diving at night off the coasts of Florida in the US and Tahiti in French Polynesia, have captured stunning photographs of juvenile fish holding larva in their mouths to seemingly ward off hungry predators.
These rare underwater encounters featured young filefish, driftfish, pomfrets and a horse-eye jack, each seen carrying or closely interacting with larvae from tube anemones or button polyps.
The photographs and analysis are published in a paper in the Journal of Fish Biology.
“Some species of vulnerable larval or juvenile fish use invertebrate species apparently for defensive purposes,” says Rich Collins, one of the divers who contributed to the article and a consultant at the Florida Museum of Natural History.
“They’ll find something that’s noxious or stingy, and they just carry it around.”
Juvenile filefish carrying a palythoa larva in its mouth. Credit: Rich Collins
A Myers’ pomfret was seen holding a button polyp in its pelvic-fin rays, while the other fish were documented actively swim with larvae in their mouths.
“The fish was able to swim actively with the zoanthid in its mouth and demonstrated a defensive posture, moving short distances and not attempting to flee during the first 2 attempts of R. Collins to collect the zoanthid,” the authors describe in the study.
“In the third attempt, the Aluterus released the larval zoanthid and swam away. The zoanthid was undamaged, with no signs of abrasion from the holding/biting behaviour.”
A horse-eye jack was also observed swimming around a larval tube anemone, which it tried to keep between itself and the camera.
In associations where fishes do not actively hold their host (biting or riding), the authors say, they may use the invertebrates as a barrier against predators.
Juvenile bamidae holding an anemone in its mouth. Credit: Linda Ianniello
The findings suggest the behaviour could be a new form of ‘mutualistic symbiosis’ which benefits both the fish and anemone.
This is because, while the sting from a larval anemone might not be enough to kill a predator, it would be “unpalatable,” says Gabriel Afonso, study lead author and PhD student at the Virginia Institute of Marine Science, USA.
Larval anemones may also benefit from being carried by the fish as a form of dispersion.
“The anemones have a relatively low speed compared to juvenile fish,” says Afonso.
“As far as I know, this is the first relationship of an open water fish interacting physically with an anemone that looks to be carrying the invertebrate.”