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Synodontis schoutedeni catfish (Credit: Oliver Drescher)

So what’s so amazing about catfish?  So far, Ferrebeekeeper has describing all sorts of different variations of these fascinating fish. From the giant truck-sized catfish of the Mekong, to the infinitesimal (yet horrifying) candirus of the Amazon, to the deadly poisonous schooling catfish of coral reefs, to catfish that live underground or in gardens, we have seen a seemingly impossible variety of the irrepressible whiskered creatures. But, aside from their variety, hardiness, and interesting appearance, catfish represent an extraordinary apogee in sensory ability.  They are able to apprehend their watery realms in ways that might as well be supernatural or alien to us.  Catfish have honed familiar senses—taste, smell, touch, hearing, and sight–to outrageous extremes. Yet they have additional senses—electroreceptivity, pressure sensitivity, and possibly other senses–that we are only starting to understand.

Channel catfish, Ictalurus punctatus

Let’s start with catfish’s sense of taste: catfish, unlike us, are not limited to tasting things with their tongues.  Their entire bodies are covered with taste buds.  To quote catfish expert Dr. John Caprio of Louisiana State University, “Catfish are swimming tongues…You can’t touch any place on a catfish without touching thousands of taste buds. To use an analogy, it’s as if the tip of your tongue grew out and covered your body.”  Catfish can literally taste the water all around their bodies and the mud they are swimming over.

Red-tailed Catfish, Phractocephalus hemioliopterus (Photo by Chad Cullen)

Beyond their powers of taste, catfish have a bloodhound-like sense of smell. With astonishingly sensitive olfactory pits near their nostrils, Catfish can smell certain compounds at one part per 10 billion parts of water. The sense of smell does not merely help them while hunting and seeking food, catfish use smell to identify other individual catfish and to maintain a social hierarchy.  A catfish has an elaborate picture of its watery realm, the denizens thereof, and of the history and interaction of these inhabitants based on smell.

Catfish Barbels

Catfish’s scale-free skin is unusually sensitive to touch but that is not the end of catfish’s ability to feel what is going on around it.  The most distinctive feature of catfish—their 8 barbels (whiskers) are literally organs for touching.  Like a blind man’s cane, each of these barbels can touch the substrate or whatever is moving in front of the catfish.  Not only are the barbels covered with taste buds and feeling nerves, the whiskers also vibrate with water disturbance and provide a sense almost like hearing—although catfish also have multiple hearing organs.

Black Bullhead Catfish (notice the prominent lateral line)

Vibrations travel well under water and most fish have excellent abilities to sense sound, but catfish have evolved some additional auditory features.  The swim bladder of a catfish (which the fish uses like a submarine ballast in order to rise and fall through the water column) is connected by a series of small bones (the Weberian apparatus) to the hearing apparatus (otoliths) inside the head. Catfish are therefore able to hear sounds of a higher frequency than other freshwater fish.  Catfish can also sense extremely low-frequency sounds thanks to a different hearing system—a series of small pores running along the fish’s lateral lines. Within the pores are infinitesimal hair-like sensing apparatuses which respond to the slightest water displacement. Using lateral line hearing, a Catfish can sense animals scuttling across the rocks on the bottom of a river, predators swimming above them, and even fishermen walking on the shore. Perhaps most remarkably, the low frequency sensors which catfish have in their lateral lines seem to give the fish the ability to detect seismic activity.  The Chinese and Japanese are said to have used the creatures as advanced earthquake detectors (which probably gave rise to the myth of Namazu, the Japanese earthquake catfish).

Although some catfish have small or underdeveloped eyes, the majority of catfish species can see extremely well. Additionally catfish possess a tapetum lucidum—a layer of reflective tissue at the back of the eyes which allows them to see keenly in low-light conditions (cat owners will recognize the tapetum lucidum as the flashing green glow of feline eyes).

Catfish in an Aquarium (further documentation required)

Finally catfish can sense the electrical discharges within the nervous and electrical-muscular systems of living things (in fact the electrical catfish goes a step beyond and uses electricity for hunting and self-defense).  The cells responsible for electroreception are found grouped together in tiny pits along the catfish’s head and along its lateral line.  Although electroreception has limited range, it is a powerful sense which can allow the fish to sense animals hidden beneath the mud or otherwise camouflaged.

A catfish’s life must be exciting—awash as they are in complicated overlaying sensory perceptions.  Their abilities to perceive the world have taken them farther than other fish. According to the Tree of Life web project:

Catfishes are a species rich and exceptionally diverse group of fishes ranking second or third among orders of vertebrates. The Catalog of Fishes (Eschmeyer, 1998 et seq.) database treats 2,855 species of catfishes as valid. About 1 in 4 valid species of freshwater fishes, 1 in 10 fishes, and 1 in 20 vertebrates, is a catfish.

Several hundred more species of catfish have been discovered since the above paragraph was written.  Paleontologists have even discovered fossils of catfish on Antarctica (the only continent where they can not currently be found living). Catfish are basically sentient sense-organs.  They have diversified and thrived by being able to discern what is going on in the world around them (and they have probably enjoyed the experience).

Ancistrus Bristelnose Catfish

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