You've likely heard of Batman. You've probably heard of the batmobile. But, you may not have heard of batfish!
What is a batfish?
The term "batfish" applies to members of the genus Platax and several other unrelated species. However, only the five Platax species are true batfishes. True batfishes are a sub-group of spadefishes, a family of 20 marine fish with flattened oval bodies, triangle-shaped dorsal and anal fins and vertical lines to camouflage their eyes. Overall - they are spade-shaped as the name would suggest.
The Platax batfishes are a bit more specialised than the other spadefishes. They are similar in appearance to the other spadefishes as adults, but as juveniles they possess long, flowing fins from which they draw their names.
These long fins allow the vulnerable juveniles to camouflage themselves in a variety of ways. Batfish superficially resemble large butterflyfish, especially in their juvenile-adult transitional state.
Five batfish species
There are only five members of the true batfish genus, Platax, although some "honourable mentions" will be revealed later. These five fish all change appearance drastically between the juvenile and adult phase of their lifecycles, so take a look at the longfinned, orbicular, dusky and humpback batfishes and the golden spadefish (also a batfish):
Juvenile longfinned batfish
Juvenile longfinned batfish tend to follow around pieces of floating ocean debris, particularly fragments or mats of seaweed. Their long, elegant fins allow them to mimic the sway of algae fronds, while their dark colouration allows them to make full use of the shadows provided by their floating shelters.
Juvenile humpback batfish
Certainly the most flamboyant juvenile on the list! Juvenile humpback batfish are the only type that don’t use their fins as camouflage, instead, they actively mimic the venomous devil firefish to keep would-be predators away.
Four of the five batfish species are migrants or residents of South African waters, particularly the warm coastal waters of KwaZulu-Natal. Two of these species, the longfinned batfish and the orbicular batfish, are most common and are also on display at the Two Oceans Aquarium, so we'll look at them in greater detail.
Longfinned batfish have the widest range of all batfishes, from South Africa and the Red Sea on the East African coast to the Pacific coasts of North and Central America and almost all the coast in between. They have also invaded the Mediterranean Sea via the Suez Canal as part of the Lessepian Migration, with well-established populations off the coasts of Israel and Turkey. Longfinned batfish are large, growing up to 60cm. As adults, they can be distinguished from the other batfishes by the dark blotch below their pectoral fins and along the bottom edge of their anal fins.
Juvenile batfish have anal and dorsal fins that are much longer and larger than their bodies and are more darkly coloured than their adult counterparts. These long, floppy fins are used to mimic the sway of floating marine debris, such as seaweed, and are used as camouflage to hide amongst drift lines. If the juvenile is living on a reef, rather than with debris in the open water, it can lie on its side and pretend to be a flatworm or nudibranch when threatened.
As juveniles, longfinned batfish take refuge in the shadows of floating marine debris. They are highly social and tend to form schools with the fish that they meet as juveniles - this often includes fish of different species. Because of this friendly nature, and their affinity for large, shady objects, juvenile longfinned batfish will often approach divers.
As juveniles are carried away from the reef, they will follow pieces of floating debris. As they meet other batfish, they will form groups that stay together for the rest of their lives. As they mature and their fins shorten, adult batfish will take up residence in lagoons, around protected reefs, inside shipwrecks or under floating mats of seaweed. Adults that are not part of a group tend to be pelagic and travel the open ocean.
They are omnivores, feeding on plankton, anemones, coral and algae.
Orbicular batfish closely resemble longfinned batfish, especially as adults. It can be quite difficult to tell the two apart, but adult orbicular batfish tend to have transparent tails with a faint brown band that helps distinguish them from the dark-tailed adult longfinned batfish.
Like the longfinned batfish, juvenile orbicular batfish rely on their long fins to mimic dead leaves. However, they have a great affinity for coastal environments, particularly mangroves and can change their colour to a rusty brown to more closely resemble leaves (the ones at the Aquarium are silver because they are small sub-adults, not juveniles).
As they grow larger, they take on a silver colouration more closely resembling the longfinned batfish. They will move out of their sheltered coastal habitats to reefs where they will feed primarily on algae but will snack on small fish if given the opportunity. Perhaps their strangest dietary quirk, orbicular batfish will often follow sea turtles around... to eat their poop.
The wide ranges of the batfish species gives their population greater resilience than many less fortunate fish species. Both the longfinned and orbicular batfish are classified as Least Concern on the IUCN Red List, while the other three species are yet to be classified.
With the exception of the longfinned batfish, all batfish rely on sensitive environments to serve are refuges for their young, eg. coral reefs for the golden spadefish and mangroves for orbicular batfish. These habitats are under threat in many parts of the world and are sensitive to the effects of climate change and their destruction will likely also affect the batfish population.
Batfish are sometimes caught by sport fishermen, but are rarely eaten due to their unappetising texture. Young batfish, particularly dusky and humpback batfish are sometimes caught for the home aquarium trade (often marketed as pinnate and zebra batfish), but as they grow large very quickly and are difficult to care for, there is little demand for them. Direct human actions do not appear to be a major threat to batfish at this point.
Honourable mention: The batfishes that aren't batfishes
Not all "batfish" are "batfish", although the fish below carry the batfish name, they are unrelated species.
Be sure to pay a visit to these unique batfish the next time you stop by the Two Oceans Aquarium. You can find the juvenile longfinned batfish and sub-adult orbicular batfish in the Tropical Cylinder of the Skretting Diversity Gallery, and adult longfinned batfish in the open waters of the I&J Ocean Exhibit.