Taxonomy: The Opistognathidae family consists of three genera with over 80 species. There is a lot of taxonomic uncertainty when classifying jawfishes. They are classified under the order Perciformes but they are hard to define because members don’t have a shared characteristic. Eighteen of these in two genera are from Australia and many are endemic. They live in areas that are hard to sample and new species are still being discovered. Common names for Opistognathidae include: Jawfishes, Grinners, Harlequins, Missing Links, MonkeyFish, Pugs, and Smiler (Bray 2021).
Anatomy: Jawfishes are slender fishes with large heads and a large upper jaw. Teeth are small and present on jaws. They have prominent eyes near dorsal surface of head and big terminal mouths. Normally have a single long dorsal fin with unbranched and thickened outermost pelvic fin rays. Caudal fin is rounded. They do not normally have head scales. Small body scales that are normally cycloid. Lateral line runs high on body to beneath dorsal fin. Largest species are 50cm in length, most are less than 12cm. Some species have sexually dimorphic jaws, males have longer maxilla and larger nostrils. Most jawfish have bright body patterns in colors such as yellow, blue, green, and white (Bray 2021).
Habitat: Jawfishes are all over the continental shelf in the tropical seas of the Indian, Atlantic, and Pacific Oceans. Most species burrow in shallow areas by coral reefs but some inhabit bays and other species can survive in water that in almost 400 meters deep. Jawfishes excavate burrows using their large mouths. They hangout at the entrance of their burrow with only their head showing or they are hovering nearby. Jawfishes are active during the day and supposedly cover their burrow entrance with coral rubble at night. If they feel threatened, they swim into their burrow (Bray 2021).
Reproduction: Males perform courtship displays like swimming around the female of their choice showing off. Some species form monogamous pairs. Females lay eggs inside the male’s burrow and after fertilization, the male broods the eggs inside his mouth until they hatch. This type of incubation is why all jawfishes, except for the blue spotted jawfish, are mouthbrooders (Bray 2021).
Diet: Jawfish eat planktonic invertebrates (Bray 2021).
Newest Discoveries: Brazilian Dusky Jawfish (Opistognathus vicinus) was recently discovered in 2018 (Rowlett 2019). Adults have a more prominent dorsal fin spot. Another new species, Thiony’s jawfish (O. thiony) was also recently found on islands off the Brazilian coast (Trindade Island, Dogaressa Seamount, and Fernando de Noronha Archipelago). It differs from its sister species the Caribbean Mottled Jawfish (O. maxillosus) by having its dorsal fin further back. Named after a Brazilian ichthyology Thiony Simon who passed in 2016. His work was over the unique fauna of isolated reef systems and discovered several new species (Rowlett 2019).
Aquarium trade: Yellowhead jawfish (O. aurifrons) is the most popular of the jawfishes. New information has come out stating that there are multiple species of the Yellowhead jawfish based on small differences in the pelvic fins. Jawfish are not caught for human consumption (Rowlett 2019).
Dianne J. Bray, Jawfishes, OPISTOGNATHIDAE in Fishes of Australia, accessed 31 Mar 2021, http://18.104.22.168/home/family/236
Joe Rowlett. Two New Brazilian Jawfishes (And More to Come?). Reefs.com https://reefs.com/2018/11/03/two-new-brazilian-jawfishes-and-more-to-come/