Fish
Oyster Toadfish
Opsanus tau · also called oyster toadfish, oyster cracker, ugly toad
The oyster toadfish is a squat, warty, foul-tempered bottom fish that most anglers are disappointed to catch. But it is a scientific star. It hums like a foghorn using the fastest muscle known in any backboned animal, it survives conditions that would kill almost any other fish, and NASA has flown it into orbit to study how the inner ear senses gravity.
Overview
The oyster toadfish lives along the western Atlantic coast of the United States, from Cape Cod to Florida, on oyster bars, eelgrass, pilings, and wrecks. It is usually 25–38 cm long, with a broad flat head, a huge mouth, fleshy jaw flaps, and mottled, scaleless, warty brown skin. It ambushes crabs, shrimp, and small fish.
The hum
A male produces a loud, foghorn-like boat-whistle hum by contracting sonic muscles against his swim bladder up to 200 times a second, calling through the night to attract females to his nest. Those muscles are the fastest-contracting muscles known in any vertebrate — several times faster than a hummingbird’s flight muscles.
In space
Because it is so hardy and its balance organs are built much like ours, NASA carried oyster toadfish on Space Shuttle missions in the 1990s to study how the inner ear develops and adjusts in weightlessness.
Status
The oyster toadfish is Least Concern, common, and — being nearly indestructible — widely used as a laboratory animal. The male guards a nest of sticky eggs on his den ceiling and stays with the young for weeks.
Oyster Toadfish: common questions
Why does the oyster toadfish hum?
The hum is a male advertisement call, produced during the spring and summer breeding season to attract females to a nest site he has claimed. He contracts a pair of specialised muscles wrapped around the swim bladder, the gas-filled organ most fish use for buoyancy, making it vibrate and boom. A female that likes a male's call enters his den and attaches her eggs to the ceiling, after which he guards them. The chorus of many males calling from a shallow bay can be loud enough to hear from a boat or a dock, and it once puzzled people who did not know a fish was making it.
What makes its sound muscle so remarkable?
Speed. To produce a steady 200-hertz tone, the toadfish's sonic muscles have to contract and relax about 200 times every second, and to do that they have an extreme version of the machinery all muscle uses, with very fast calcium handling and an unusual structure. They are the fastest-contracting muscles measured in any vertebrate, several times faster than the muscles that power a hummingbird's wingbeat or a rattlesnake's rattle, which is why the toadfish is a favourite subject for scientists studying how muscle works.
Why did NASA send toadfish to space?
To learn how the vestibular system, the part of the inner ear that senses gravity and acceleration, copes with weightlessness. The toadfish's balance organs contain tiny stones, called otoliths, that sit on sensory hair cells and are pulled by gravity, an arrangement very similar to the one in the human inner ear. Toadfish are also small, cheap, and exceptionally robust, surviving the vibration and stress of a rocket launch that would kill more delicate animals. Studying how their balance organs developed and adjusted in orbit helped researchers understand the disorientation and motion sickness that astronauts experience.
Is the oyster toadfish dangerous or good to eat?
It is not dangerous, though it can give a hard, crushing bite if you put a finger near its mouth, and the spines in its dorsal fin and gill covers can prick and cause a painful but minor wound, sometimes with mild irritation. It is edible, with firm white flesh, and is occasionally sold or eaten under names like oyster cracker, but it is bony, unappealing to look at, and not widely marketed. Most anglers who catch one, hoping for something else, simply unhook it and throw it back, which the toadfish, being nearly indestructible, tolerates well.