Reef fishes

Among the thousands of inhabitants in a reef, fishes stand out as colorful and interesting to watch. Hundreds of species can exist in a small area of a healthy reef, many of them hidden or well camouflaged. Reef fish have developed many ingenious specializations adapted to survival on the reefs. And although coral reefs occupy less than one percent of the surface area of the world oceans, they provide a home for 25 percent of all marine fish species [1]!

A prominent group of reef fishes are the butterflyfish of the Chaetodontidae family. Butterflyfishes are particularly picky about their food and shelter needs, that’s why they are often used as a proxy for the health status of coral reefs. They are so-to-say the “canary in the coal mine” [2].

A pair of Chaetodon semilarvatus - Bluecheek butterflyfish

Butterflyfish got their names because of their attractive body coloration. They can be black, orange, yellow, red, silver, and white in color, with different kinds of spots and patterns on their body. Many species have black stripes across their eyes and eye-like spots on the body. Both stripes and spots are assumed to confuse the predators and therefore allow the butterflyfish to escape on time - which is needed, as they have many predators - large fish, sharks and eels often prey on them [3]!

Chaetodon lunula - the 'Racoon butterflyfish'

Another common species that you might find at or close to a reef are ‘batfishes’, especially the juveniles. The common name ‘batfish’ is actually given to several fish species, but here we are referring to the Platax genus. Platax batfishes can be found in reefs throughout the entire Indo-Pacific region, most of them in higher latitudes. They are very common around reefs and shipwrecks, either solitary, swimming on their own, or in bigger groups. Batfish are extremely intelligent and are a fascinating species of marine fish. During fieldwork, they are often accompanying us, seemingly very interested in the work we do.

A curious batfish accompanying a marine scientist during her dive. Batfishes of the genus Platax are also a prime example of a species that looks quite different in its juvenile state when compared to the adult. Juveniles are characterized by their distinctly bat-like side profile. They have a tall, laterally compressed body and two long anal and dorsal fins. However, as it matures it loses its distinct shape and its body becomes more elongated and square-shaped. Adults are also less striking in color and their bodies take on a silvery grey coloration.

Left: Platax adult; Right: Platax juvenile

References [1] Mcallister, D. E. (1991). What is the status of the world’s coral reef fishes. Sea Wind, 5(1), 14-18. [2] Crosby, Michael P., and Ernst Reese. "A manual for monitoring coral reefs with indicator species: butterflyfishes as indicators of change on Indo-Pacific reefs." (1996). [3] Kelley, Jennifer L., John L. Fitzpatrick, and Sami Merilaita. "Spots and stripes: ecology and colour pattern evolution in butterflyfishes." Proceedings of the Royal Society B: Biological Sciences 280.1757 (2013): 20122730.