Understanding Catfish Senses
September 28, 2010
With more than 250,000 taste buds on even the smallest catfish, these game fish can rightly be called "swimming tongues." But that's just the tip of the sensory iceberg when it comes to catfish.
Photo by Ron Sinfelt
To most folks, catfish don't inspire much admiration. They're great on a dinner plate with a side of hushpuppies, for sure. And no one could dispute the fact that they're among the fightingest fish in fresh water. But there's really nothing special about a catfish, right?
Well, guess again, friend. Catfish are among the most extraordinary animals on earth. More than 2,200 species swim the waters of the world (about 8 percent of the total number of fishes). They're found on every continent except Antarctica and comprise what many fish scientists consider the most diverse group of fishes on earth.
Perhaps the most amazing thing about catfish is their astounding sensory abilities. No fish have more finely honed senses of taste, touch, smell and hearing to keep them attuned to their environment. In fact, the sensory abilities of catfish are like something out of Ripley's Believe It or Not.
A catfish just 6 inches long has more than a quarter-million taste buds on its body. On a giant blue cat or flathead . . . well, who knows? No one wants to count.
The mouth and gill rakers are packed with taste buds, and the sensory organs cover the outside of the catfish as well - the whiskers, fins, back, belly, sides and even the tail. If you were a catfish, you could taste a slice of pizza just by sitting on it.
"Catfish are swimming tongues," says Dr. John Caprio of Louisiana State University. "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."
Caprio, a neurophysiologist, has studied what fish taste and smell since 1971. His research has given him extraordinary insights into catfish feeding behavior, insights that can help you understand what makes catfish bite.
"The catfish's sense of smell is equally keen," says Caprio. "Catfish can smell some compounds at one part to 10 billion parts of water."
Water flows over folds of highly sensitive tissue inside the catfish's nostrils, allowing the fish to detect certain substances in its environment. The number of these folds seems related to sharpness of smell. Channel cats have more than 140. Rainbow trout have only 18, and largemouth bass have just eight to 13.
Many catfish anglers believe smelly baits are best for catfish, but Caprio disputes this.
"Most anglers think horrible-smelling baits work best," he notes. "But that's crazy. What stinks to you doesn't stink to fish. You're smelling chemicals volatilized to the air, but animals living in water can't detect them. They detect chemical compounds in the water. What you're smelling, fish can't smell."
With no visible ears, it might seem that catfish can't hear well, but that's not true. A catfish's body is the same density as water, so it doesn't need external ears. Sound waves traveling through water go right through a catfish as well. When sound waves hit the fish's swim bladder, the bladder starts vibrating. This amplifies sound waves, which then travel to small bones (otoliths) in the inner ear. The otoliths start vibrating, too, and as they vibrate, they bend little hairlike projections on the cells beneath them. Nerves in these cells carry a sound message to the brain.
The swim bladder on most fish is independent of the inner ear, but in catfish, a series of bones connects the swim bladder and inner ear. Fish without these bone connections (e.g., bass and trout) can detect sounds from about 20 to 1,000 cycles per second. The hearing of catfish, however, is much more acute. They can hear sounds of much higher frequency, up to about 13,000 cycles per second.
Low-frequency sounds undetectable by the catfish's inner ear are picked up by the lateral line, a series of little pores along the fish's sides. Inside the pores are cells with hairlike projections. These projections bend in response to water displacements, thus stimulating nerve endings that signal the brain. The catfish uses this system to locate nearby prey, potential enemies and other catfish. Creatures scurrying across the bottom, flopping at the surface, swimming through the water or walking along a riverbank all create low-frequency vibrations the lateral line detects.
"This 'vibrational' sense is very well developed in catfish," Caprio notes. "The Chinese have used catfish for centuries to warn of earthquakes. Catfish can detect days in advance a lot of earthquakes because they have an ultra-sensitivity to low frequency vibrations."
TOUCH AND SIGHT
Catfish also have excellent senses of touch and sight. "Channel catfish, in particular, have great eyesight," says Caprio. "The eye of the channel catfish is used in many medical centers for research in vision."
Caprio points out that channel cats in clear water - and other species as well - often will strike fishing lures with no sensory cues other than sight triggering the action. They see something that looks like prey, and they attack.
The lack of scales heightens the catfish's sense of touch as well. Their smooth skin is very sensitive, and the brush of wiry fishing line or something else out of place in their environment may send them scurrying.
Most extraordinary of all, perhaps, is a sense called electroreception. Catfish don't have to see prey or smell it or taste it. Tiny clusters of special cells on the head and along the lateral line detect electrical fields in living organisms. A catfish can find its prey through electroreception, just like sharks.
"A catfish has electroreceptors all over its head," says Caprio. "These little pores go to electric sensory receptors. They work because every living cell is a battery. That is, if you stick an electrode inside a cell and outside a cell, you get some kind of reading just as if you were measuring a battery with a voltmeter. So catfish use the electric sense to help them find food. It's a close sense; they must be within centimeters of the object. Catfish can dig in the mud and find insect larvae, worms and such by using their electric sense alone."
ANATOMY OF THE BITE
All the senses interact when a catfish seeks something to eat. The sensory organs detect chemicals, vibrations and/or electric charges from potential food items and send messages to the fish's brain telling
it to find the food. Then, when the cat picks up the food, taste buds in the mouth relay messages to another part of the brain and tell it to eat the food - or spit it out.
"All the catfish's senses are used," says Caprio. "It's like going to a restaurant. You walk in. It looks and smells good, so you order a steak. The waiter brings it on a covered platter; it smells great. You really want this steak, but when the waiter lifts the top, the steak is blue. Now you don't want it.
"You see, many sensory cues control your feeding behavior. The same thing with fish. A catfish doesn't just search with its nose or taste buds or eyes. It uses every sensory cue available before deciding to eat."
If a catfish tastes or smells certain compounds in the water or on your bait, feeding activities may cease. These compounds include such things as gasoline and certain ingredients in sunscreen, tobacco, insect repellent and other items commonly used by fishermen. You'll catch more cats if you avoid contact with such materials as much as possible.
Vision, however, is the sense most likely to cause fright in a catfish, Caprio says.
"If a bird flies overhead, or someone casts a shadow that moves across the water, all feeding may cease," he says. "We have fouled up lab experiments for weeks just by having someone put their hand over the top of a tank. If you tape the silhouette of a bird predator to the top of a fish's tank, that cat won't come out to eat, no matter how hungry it gets. The fish will die before he goes out and gets food right in front of it, unless you turn the lights off; then he'll come out and get it. That's one reason many catfishermen are more successful when fishing at night."
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The exceptionally powerful senses of catfish enable them to thrive in a wide variety of habitats. They cope better than other fish in difficult environments, and thus are often found where other fish are not. The next time you feel a big one tugging on your line, think about how it found your bait. It will help you better appreciate the remarkable senses of these extraordinary fish.