Off the coast of Tahiti, small fish have developed great adaptations to avoid becoming prey. Divers have photographed a small, silvery half-dollar-shaped fish, known as Myers’ Pomfret, with the scientific name Brama Myers“Riding” Anhozoan larva or sea anemone.
With the invertebrate carefully tucked between the fish’s pelvic fin, divers hypothesize that the small fish was using the anemone as a weapon of sorts, perhaps deploying its stinging cells to defend itself against potential predators.
Learn more: Friends and anemones: how clownfish strengthen symbiotic bonds with their hosts
Fish and anemone: a symbiotic relationship
Juvenile filefish carrying a palythoa larva in its mouth.
(Image credit: Rich Collins)
This is not the only time this type of symbiotic relationship between juvenile fish and anemone larvae has been observed. In West Palm Beach, Florida, newly hatched fish species have been spotted carrying anemone larvae in their mouths, trapping the invertebrates with their sharp teeth.
A fish carrying its anemone larva in its mouth swam actively, demonstrating what the researchers called a “defensive posture, moving short distances and not attempting to flee.” The fish eventually released the anemone, which was unharmed, and swam away, suggesting that the fish was not trying to eat the anemone.
The symbiotic relationships between anemone and fish are well documented – just ask any fan of Finding Nemo. The poisonous anemone protects the fish, while its inhabitant, in turn, provides nutrients to its host.
But the photographs recently published in the Journal of Fish Biology suggest that these anemonefish and anemonefish relationships are much deeper and more diverse than previously thought.
A spicy shield
Juvenile Bamidae holding an anemone in its mouth.
(Image credit: Linda Ianniello)
“Some species of vulnerable larvae or juveniles use invertebrate species apparently for defensive purposes,” Rich Collins, a diver and consultant at the Florida Museum of Natural History, said in a statement. “They’ll find something harmful or stingy, and they’ll just carry it around.”
Various photographs captured during blackwater drift dives, when divers drift through deep, open water at night to photograph marine life, between 7:30 p.m. and 10:00 p.m. The dive team captured a few images at depths of up to 60 feet, all in the epipelagic zone, where daylight still reaches the depths.
The team noted a variety of fish species associated with the anemones – limes, drift fish, pomfrets and a juvenile trevally were all seen carrying larval tube anemones or button polyps in their mouths.
Anthozoans are marine organisms that lack bones, including corals, sea fans and anemones. These invertebrates also have stinging polyps and nematocysts, microscopic harpoon-like cells that release a venomous thread on contact. The sting of an anemone larva would not kill a potential predator, but Gabriel Alfonso, lead author of the study, said it would be “unpleasant.”
New mutual benefits
The images may also reveal evidence of an entirely new form of mutualism between the two species: the fish benefit from protection. In return, the anemone could benefit from transport to new areas.
“Fish in early developmental stages have distinct survival strategies when interacting with pelagic invertebrates, such as hiding inside, imitating potentially harmful, venomous, unpalatable, and/or low-nutrition invertebrate patterns, or swimming alongside and maintaining associations between fish and anthozoans in epipelagic waters,” the study authors wrote.
Collected by citizen scientists, these images highlight the importance of the emerging field of blackwater photography and how community science can improve our understanding of the world’s oceans.
“This new data source offers many insights that were previously inaccessible through fixed specimens from scientific surveys, including life color, behavior, and association with other planktonic organisms,” the authors concluded. “Therefore, we highlight the importance of community science for the advancement of ichthyology by emphasizing its connection to the blackwater diving community.”
Learn more: 7 surprising symbiotic relationships and how species help each other to survive
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