About This Species
If the Threadfin Butterflyfish looks familiar, it's because it is a staple of saltwater fish tanks—or because you spend a lot of time in the tropics. The exotic fish, also known as the Diagonal Butterflyfish or the Cross-stripe Butterflyfish, is yellow, black and white, though it looks slightly different depending on where it lives. Those in the Red Sea, for instance, lack the distinctive black spot, or "false eye," on its dorsal fin, which can help confuse predators.
Though often found around coral reefs, the Threadfin Butterflyfish is not dependent on the reefs. It's more of a generalist feeder, with a diet of invertebrates and algae, which can also be found among mangroves and rocky habitats. It can be seen on its own, in pairs or in large groups, searching for food in tropical waters. The fish is monogamous and will stay with its mate for years.
The Threadfin Butterflyfish is listed as a species of least concern by the International Union for Conservation of Nature and Natural Resources, meaning its population is stable. The IUCN does note, though, that some local populations of the fish have declined when coral reef is lost, although the fish doesn't feed on corals.
According to a recent study in the journal Biology Letters, the Threadfin Butterflyfish, as well as a few other tropical species, have a seasonal home off the southeast coast of Australia. According to the study, the larvae of these fish ride the East Australian Current down from the Great Barrier Reef and make this new region their home from January to May (Australian summer). But by July, when the ocean is colder, the juvenile Butterflyfish and the other tropical fish die off.
The Threadfin Butterflyfish's Range
The Threadfin Butterflyfish is found in a variety of tropical waters. They are found throughout the Indian and Pacific oceans, in the Red Sea and off the eastern coast of Africa, and near Hawaii and Japan. This map shows the fish's natural range and the probability of its occurence in different regions.
The Threadfin Butterflyfish, like many fish that are suited to warmer waters, is well-prepared for climate change. But its success in navigating warmer waters has consequences. The Biology Letters study found that Threadfin Butterflyfish is among a handful of tropical species that, within 10 years, will be able to make a new, year-round home off the southeastern coast of Australia. That region is a known hotspot, with accelerated warming.
The study's authors found that of all of the tropical species the are showing up in the region, the Threadfin Butterflyfish is among the most well-suited to thrive there because it can live in varying habitats. It's unknown how the fish would impact the existing ecosystem there, but it would be competing with native species for both food and habitat resources.