Catfish inhabit tidal rivers of the Atlantic coast through the crystal streams of the Ozarks to the murkiest reservoirs of the Plains States. They thrive in still ponds and maneuver tailraces that would stop a salmon. They eat day or night on animal and vegetable matter, living and dead, under a frozen sheet of ice in winter and during summer in water approaching 100°F.
Such adaptability demands a highly sensitive nervous systems with the ability to check every relevant environmental cue. Catfish senses locate prey, avoid predators, return to familiar spots after months of absence, and find mates in murky blackness. How?
Smell and Taste
Catfish are a great blend of specialist and generalist, with exceptional senses of smell and taste, good vision, plus acute senses of feeling and hearing. The senses of taste and smell detect molecules of substances dissolved in water. Because of their similarity, scientists sometimes lump both senses as “chemoreception.”
For catfish, chemoreception is critical for finding prey, avoiding predators, locating fish of the same species, coordinating spawning time, and homing to residence areas or spawning sites. Olfaction (sense of smell) detects substances from afar while taste usually determines the palatability of a substance once it’s bitten into. Catfish, however, can taste items without biting them, even at a distance of 15 feet or so.
Catfish and most other fish have two small openings called “nares” on either side of the snout, that lead to small chambers with a series of folds. Channel catfish have over 140 folds, more than any other freshwater fish. These folds increase the surface area used for smelling. Hairlike projections on the folds act as olfactory receptors.
Channel cats are able to detect several amino acids at concentrations of one part per 100 million. That’s roughly equivalent to an ounce of a substance dissolved in 100,000 railroad tank cars. The fish with the most acute sense of smell, by the way, is the American eel, capable of detecting substances at less than one part per trillion. Salmon and rainbow trout, anadromous species that must detect the scent of their stream of birth from long distances, match the catfish’s olfactory powers.
This keen sense of smell guides cats to your bait lying 100 yards upstream in a muddy river in the middle of the night. Put a bait in the water and cats will find it. Scientific tests indicate that bullheads have a significantly weaker sense of smell, though better than most scaled fish. They use pheromones to maintain a social hierarchy among a group of fish; each member of a group has a unique fragrance that other bullheads recognize, and this smell also indicates their status in the group.
What bullheads sacrifice in sensitivity of smell, they make up for in taste. Dr. John Bardach and colleagues at the University of Michigan conducted experiments that demonstrate that bullheads can taste their way to a food source over a distance of more than 25 body lengths. Fish apparently decided which direction to swim by comparing how strongly the taste receptors on either side of the body were stimulated.
Catfish have more than 175,000 taste buds on the surface of their bodies, making them virtual swimming tongues. The gills contain the highest concentration of taste buds, followed by the barbels and the mouth.
Experiments show that blind catfish can find food with their senses of smell and taste, plus their hearing and lateral line. In some rivers, vision extends no more than a couple inches. Yet all catfish species see well, except of course the blind catfish species found in Texas.
Channel and blue cats have particularly good vision, attacking fast-moving crankbaits and at times cornering schools of shad. In Idaho’s Brownlee Reservoir, channel cats rise to sip zooplankton when wind concentrates this food source.
Catfish in aquaria often watch as people cross the room or approach to feed them. Catfish eyes, like the eyes of most other fish, have six sets of muscles to shift eye position. Their retinas also contain a tapetum lucidum, a reflective layer of guanine crystals on the back of the eye that reflects light at night.
This feature, which is most prominent in walleyes, aids night vision by reflecting light back over the rods, structures used for vision in dim light. Cones, the other type of vision cells, discriminate colors in daylight. Although behavioral experiments to determine a catfish’s ability to see color haven’t been done, the characteristics of their cones indicate that they discern colors.
Hearing and Lateral Line Senses
To understand fish’s hearing and their unique lateral line sense, visualize sound as waves. In air and water, different sounds give off varying wave frequencies. Fish hear with inner ears much like ours. The inner ear contains three semicircular canals for balance and three fluid-filled saclike structures for hearing. These sacs, lined with cells covered with fine hairlike projections, contain three calcium carbonate earbones called otoliths.
Sound waves moving through water pass through a fish’s body as if it weren’t there because their body density nearly matches the density of water. When sound waves reach the otoliths, which are about three times denser than fish flesh, they vibrate at a rate different from the tissue surrounding them. Vibrations bend the hairlike projections on the cells, and nerves carry a sound message to the brain.
Catfish can hear sounds of much higher frequency (up to 13,000 cycles per second) than other common gamefish. Catfish and minnows hear better than bass, trout, and other common gamefish because they have Weberian ossicles, bony structures that connect the swim bladder to the inner ear. The bladder acts as a resonating chamber to amplify vibrations, improving sensitivity and hearing range. Fish without Weberian ossicles hear sounds only from about 20 to 1,000 cycles per second.
Catfish and other fish species detect low-frequency underwater vibrations (from 1 to about 200 cycles per second) with their lateral line. This specialized sensory organ consists of a series of pores running in a line down each side of the fish’s body. Each pore contains cells with hairlike processes, similar to those of the inner ear.
These hair cells, called neuromasts, receive low-frequency sound waves and send a nerve impulse to the brain. Overlap occurs between frequencies catfish hear and those they feel with their lateral line. But hearing dominates when a sound originates far from the fish, while the lateral line becomes increasingly important when objects are closer.
Some sensory cells in both the inner ear and lateral line are oriented in one direction, others in the opposite direction. This helps fish pinpoint the source of sound.
We know rather little about sense of feel in fish, though certainly river fish use the pressure of current to direct their upstream and downstream movements. North American catfish lack scales — except for the exotic armored cats that have become established in some warm climates — making them more vulnerable to skin injuries than are common scaled species.
But the skin of catfish must offer advantages like sensitivity for feeling cover objects like rocks and brush, and for flexibility in turning. Flathead catfish seem soothed when they’re tickled under the chin or their belly is rubbed, a trait noodlers take advantage of when reaching into crevices to grab cats.
Catfish certainly are a sensitive lot with their senses of taste, smell, and hearing among the best of our North American fishes. Little wonder that successful anglers use nature’s own essences to tempt them to bite.