I remember my Mom, when she noted something foolish I had done, would say “you ain't got the sense God gave geese.” I was never confused about her meaning – “use the senses God gave you!” As I study different animals I am still fascinated by the special senses that each species possesses and the senses that are less developed.
North American catfishes (Ictaluridae) are nocturnal animals. They avoid well-lighted habitats during the day and leave the dark sanctuaries at dusk to feed. Catfishes have a keen sense of taste and smell, but poor vision. Taste buds are densely packed on the barbels and mouth of the catfish, as well in the skin all over the body. The nares connect highly sensitive olfactory (i.e., smell) tissue with the aqueous environment. Taste and smell assist in locating food, but catfish also use the sense of smell and taste to communicate among individuals.
Each dot represents chemosensory cells on the body of a catfish (Pough et al. 1989).
Taste buds develop very early in larval catfish -- first in the mouth, then barbels and head, and later in trunk (Landacre 1907; Northcutt 2005). John Bardach, a Professor of Fisheries at the University of Michigan, investigated the use of taste sensation as it influenced as it influenced the search for food. Most believed that smell was the primary sense to detect distant chemical clues. But bullhead catfish (Ameirus nebulosus and Ameirus natalis were the study animals) have many thousands of external taste buds on the body, with especially dense concentrations on the barbels. One study estimated there were 50 taste buds per mm2 on the pharyngeal arches (Atema 1971).
Bardach et al. (1967) investigated whether bullhead catfish could use the body taste buds, to compare the concentrations of chemical stimuli and locate by taste alone over distances. They did experiments in which they eliminated other sensory organs. Study catfish were blinded with benzethonium chloride. “Some also had their olfactory tracts severed or their nares cauterized, others had some or all of their barbels amputated, and still others had portions of their seventh cranial nerves severed just outside the cranium” (Bardach et al. 1967, p 1276). Test bullhead catfish were tracked to see how they orient toward the stimulus (either an amino acid, cysteine hydrochloride, or pork liver juice). The study apparatus was large aquarium 2 m wide and 2 m long and the test bullheads were ~23 cm.
Head of a Yellow Bullhead showing closeup of barbels. Photo by Bart Carter: www.tnfish.org
In experimental settings, a blinded catfish would perceive a chemical and show a startle response: “the barbels stiffened, the body became rigid for a moment, the head began a slow to-and-fro movement, and the fish almost immediately began swimming” (Bardach et al. 1967, p 1277). They often sought direct contact with the surface film by means of their nasal and maxillary barbels (see photo). The pattern of movement showed that the bullhead was comparing taste concentrations and moving in the direction of the release point of the stimulus (i.e., pork juice). Even without their olfactory senses, the bullheads were able to locate the source of the chemical stimulus with their taste buds alone. Even without barbels or nares, the bullheads could locate the source within 24 seconds. Therefore, taste alone plays a role in bullheads locating distant food sources. How far? No one has worked to replicate this type of study in the wild. However, many catfish anglers rely on this keen sense of smell and taste and river currents to increase the odds of catching a catfish.
Bullhead seeking barbel contact with chemical at water surface. Photo from Bardach et al. (1967).
Dr. John Todd, founder and President of John Todd Ecological Design, first investigated social behavior in bullheads. He and others were intrigued to notice bullheads exhibiting territorial behavior, dominance hierarchies, and agonistic displays. Todd et al. (1967) used operant conditioning to train yellow bullheads to associate smells from individual catfish with positive (food) or negative (electric shock) responses. Test fish were blinded so that the responses were not influenced by visual cues. The experiments convincingly demonstrated that the yellow bullheads could literally smell and remember other individuals after about 30 trials with only a 4.5% error. This sense helped to explain the development of dominance hierarchies in the bullhead catfishes. A group of catfish will know one another; there will be one dominant catfish and others are known as subordinates. If an intruder catfish enters the group’s territory, the leader will engage the intruder. It was not completely clear whether the test bullheads were reacting to the stress pheromones from mucus, fecal matter or urine. However, the ability to recognize individuals based on taste (i.e., chemosensation) suggest that complex communication occurs among the bullhead catfishes.
The largest of the three bullheads is the dominant one. When the scent of an unfamiliar catfish is detected, the two subordinate catfish enter the shelter and the dominant catfish engages the intruder. (photo from Todd 1971)
Bullhead catfishes communicate via chemical signals and interact with each other with a variety of agonistic behaviors. These agonistic behaviors vary in intensity depending on whether the individual is defending a territory or whether individuals are evenly matched.
Territorial individuals make a number of actions usually ending in a chase with the dominant fish in pursuit (Todd 1971). Removal experiments suggest that bullhead catfish not only identifies but also remembers particular individuals. The behaviors and recognition depend on the chemical cues because even blinded individuals were capable of social recognition. The chemical communication must also play a role in allowing dense aggregations of bullheads in the wild without aggressive behaviors.
Dominant bullhead chases a subordinate away from defended territory. Illustration from Todd (1971, p. 101).
Although not specifically studied, chemical communication is probably involved in the courtship and breeding behavior of catfishes. Catfish can recognize individuals according to sex and sexual maturity. Catfishes nest near natural shelters in territories guarded by males. Lawrence Blumer (1985) described individual bullheads butting or nipping and side-by-side undulation in courtship in a natural lake; his observations suggested that bullheads were monogamous in a breeding season. Both males and females chase other bullheads from the nest sites; however, males were the principal care-givers guarding the developing embryos. The field of chemical communication in fish has greatly expanded beyond the catfishes. One innovation is the use of underwater electro-olfactogram recordings that measure voltage changes from surface of the olfactory epithelium in response to odors. Further studies are needed to evaluate the importance of the communication in natural systems as well as the influence of environmental stressors on chemical communication.
Atema, J. 1971. Structures and functions of the sense of taste in catfish (Ictalurus natalis). Brain Behavior and Evolution 4:273-294.
Bardach, J.E., J.H. Todd, and R. Crickmer. 1967. Orientation by taste in fish of the genus Ictalurus. Science 155:1276-1278.
Blumer, L.S. 1985. Reproductive natural history of the Brown Bullhead Ictalurus nebulosus in Michigan. The American Midland Naturalist 114:318-330.
Landacre, F.L. 1907. On the place of origin and method of distribution of taste buds in Ameirus melas. Journal of Comparative Neurology 17:1–66.
Northcutt, R.G. 2005. Taste bud development in the channel catfish. Journal of Comparative Neurology 482:1-16.
Pough, F.H., J.B. Heiser, and W.N. McFarland.1989. Vertebrate life, Third Edition. Macmillan, London. 656 pp.
Todd, J.H. 1971. The chemical languages of fishes. Scientific American 99-106.
Todd, J.H., J. Atema, and J.E. Bardach. 1967. Chemical communication in social behavior of a fish, Yellow Bullhead (Ictalurus natalis). Science 158:672-673.