Macrognathus is a genus of eel-like fish of the family Mastacembelidae of the order Synbranchiformes. These fish are distributed throughout most of South and Southeast Asia. Macrognathus species feed on small aquatic insect larvae as well as oligochaetes.

Appearance and anatomy

Most Macrognathus species attain 20 - 25 cm in length, but a few surpass this size, with the largest being M. aral at up to 63.5 cm. Macrognathus are mostly similar to Mastacembelus. However, they differ in a more modified rostrum, which may be slightly to significantly larger and longer than those found in Mastacembelus. This serves not only to find food but also to help gather food.

In the aquarium

A number of species of this genus are popular aquarium fish. These include the lesser spiny eel, Macrognathus aculeatus, the spotfinned spiny eel, Macrognathus siamensis, as well as others.

Species

According to FishBase, there are currently 25 recognized species in this genus. According to Catalog of Fishes, one of these, M. malabaricus, belongs in the genus Mastacembelus instead of Macrognathus and another, M. taeniagaster, is considered a junior synonym of M. circumcinctus.