Surprised to meet rare copper scale arowana off the coast of California

Marine biologists on an expedition in Monterey Bay in California, USA recently discovered a rare and brilliant deep-sea fish named: the high-fin arowana (Bathophilus flemingi). This is the rarest of all arowana species, and scientists have previously only found live individuals a handful of times.

For three decades, Monterey Bay Aquarium Research Institute (MBARI) researchers have searched the depths of the bay using remote-controlled vehicles (ROVs) and they've found many wonders, including some arowana species. However, the highfin arowana has proven to be the most elusive. This particular fish was found at a depth of 300m.

Rare copper color arowana off the coast of Monterey Bay, USA.

Bruce Robison, MBARI senior scientist and lead researcher on the team that made the discovery, said: 'They are amazing animals, especially for their coloration. The arowana's scales sparkle with a metallic bronze color unlike any fish that lives in the deep sea."

The pigments that give a fish's coppery, brassy skin color can actually be a form of camouflage, as these pigments absorb the remnants of blue light causing it to go deep, making the fish almost invisible in its environment.

This camouflage is suitable for predatory fish. They hover in the dark and wait for small fish and crustaceans to swim past. However, these meals do not approach randomly. Instead, they are attracted to the arowana, which has bioluminescent fibers extending from its chin.

'It uses that lure to lure prey that see the glow, because they think it's something small enough for them to eat,' said Robison. When the prey gets close enough, the arowana's wide jaws and many teeth will squeeze down.

Arowanas use bioluminescence not only to capture food but also to avoid being eaten. 'Many predators look up to try to spot the silhouette or silhouette of their prey against the light of the waters above,' said Robison. These light organs match the color and intensity of the light above, erasing the silhouette of the fish'.

The discovery of this highfin arowana is just one of many examples where Robison's exploratory curiosity about the ocean paid off as they discovered the unexpected.