The Toadfish are a type of ray-finned fish often found on the sand and mud bottoms of coastal waters worldwide, notable for somewhat broad heads and drab coloration reminiscent of terrestrial toads, as well as for the ability of the males of some species to “sing” using their swim bladders. They are classified as the sole family Batrachoididae of the order Batrachoidiformes, and include about 70 species in 19 genera, among them the common oyster toadfish, Opsanus tau. Their spines may inflict wounds on people during handling.
Toadfish are usually scaleless, with eyes set high on large heads. Their mouths are also large, with both maxilla and premaxilla. The gills are small and occur only on the sides of the fish. The pelvic fins are forward of the pectoral fins, usually under the gills, and have one spine with several soft rays. Three are two separate dorsal fins, the first smaller dorsal fin with spines; and the second larger and longer dorsal, with from 15 to 25 soft rays. The number of vertebra range from 25 to 47.
Toadfish of the genus Porichthys, the midshipman fish, have photophores and four lateral lines, while the Thalassophryninae are venomous, with a total of four hollow spines (two dorsal and one on each gill-flap (opercle)) connecting to venom glands and capable of delivering a painful wound.
Toadfish are found worldwide. Almost all are marine, but Daector quadrizonatus and Thalassophryne amazonica are known from Colombia (Atrato River) and the Amazon River, respectively.
Toadfish are bottom-dwellers, ranging from near shore areas to deep waters. They tend to be omnivorous, eating sea worms, crustaceans, mollusks and other fish. They often hide in rock crevices, among the bottom vegetation, or even dig dens in the bottom sediments, from which they ambush their prey.
Males make the nests and guard them after the female lays the eggs. The male attracts the female by “singing”, that is by releasing air by contracting muscles on their swim bladder. The sound has been called a ‘hum’ or ‘whistle’.
Toadfish are not normally commercially exploited; however, they are taken by local fishermen as a food fish, and by trawlers where they usually end up as a source of fishmeal and oil. Some smaller toadfish from brackish-water habitats have been exported as fresh-water aquarium fish.