Catfish (Family Plotosidae)

Included among this fascinating group of fish are several species that use their pectoral fins as “legs” to travel considerable distances over land. The most famous of these, the Southeast Asian walking catfish (Clarias batrachus) was introduced into Florida in the United States as an escapee from the aquarium trade. It is now well established in breeding populations and, in fact, is the most common freshwater fish in many areas of the southern part of that state. A voracious predator, the walking catfish often decimates populations of local fish and amphibians.

Freshwater Catfish

Although catfish are to be found in both freshwater and marine environments, it is in the realm of freshwater that these truly unique and often bizarre creatures come into their own. Worldwide in distribution, they have adapted to an amazing variety of lifestyles and diets, and in the variability of their appearances they are unrivaled. Members of this huge family, which numbers more than 2,500 species, are among both the largest and the smallest of the world's freshwater fish. While many, such as the minute Corydoras pygmaeus, mature at a body length of only ½ inch, the European wels, Silurus glandis, tops out at 16½ feet and may weigh up to 660 pounds.

Although catfish seem generally harmless. the tiny candiru catfish (Vandellia cirrhosa) is feared by many, even though it shares its South American habitat with creatures that appear far more formidable. Adapted to feeding on blood in the gills of larger fish, the candiru is for some reason also drawn to urine in the water. It follows the stream to its source, enters the unfortunate victim's urethra, and extends its spines. This, as one might imagine, results in excruciating pain and necessitates surgical removal.

All catfish possess from one to four pairs of whiskerlike barbells around their mouths, from which they derive their common name. These extremely sensitive organs are studded with taste buds, enabling their owner to find food in the murkiest of waters or on the darkest of nights. It is very interesting to watch the quick reaction of nearly any species of catfish to even the tiniest particle of food introduced into the aquarium. The dorsal and pectoral fins hide stout, pointed spines, which in some species can inject prey with a potent venom.

Although very different in appearance, catfish are closely related to knife fish, one of which is the electric eel (Electrophorus electricus), which reaches a length of 7 feet and is famed for the powerful electrical discharges it can produce. At least one species of the catfish, the electric catfish, also makes use of electricity while hunting or defending itself.

In contrast to most other fish, the catfish's body is covered by a type of skin as opposed to scales. In some species, however, a scalelike plate has evolved to provide additional protection from attack.

Nearly all species of catfish engage in some form of parental care, and many take this to the extreme, with the fry following the male about and deriving protection from him for several weeks. Some types incubate the eggs in the mouth, and one African species (Synodontis punctatus) has added a unique twist to this already unusual form of reproduction. This enterprising fish takes advantage of the overly protective nature of certain mouth-brooding cichlids that share its habitat. Pairs of the catfish release their eggs in close proximity to spawning cichlids. The “foster parents” inhale the catfish eggs along with their own, thus relieving the catfish of the burden of protecting their young!

When medicating catfish, be aware that their skin allows for a greater absorption rate than do the scales of typical fish. Some fish medications have specific doses for catfish (and for other scale-less fish such as eels) or may state that the medication is not suitable for such fish. In the absence of such instructions, start with half the recommended dose and monitor your pet's reactions carefully.

Corydoras spp.

Many species of these squat, peaceful catfish, all very similar in shape but varying widely in pattern, are available to the aquarist. They are extremely engaging little creatures, constantly in motion as their vacuumlike mouths sweep substrate for food. Their ability to extract uneaten bits of food from the smallest of crevices, along with their prodigious appetites, render them nearly essential to most aquariums. They should not, however, be left to survive on leftovers alone. True, they are scavengers, but they require quite a bit of food and a balanced diet if they are to thrive. In aquariums housing active surface-feeding fish, be sure that flake food reaches the bottom of the aquarium, and also that pellet food is provided for bottom-dwelling fish such as Corydoras.

This is also one of the few catfish species to travel about in schools, and they will pair up with related species when doing so. Although they hail from the warm waters of Central and South America, most are quite adaptable in regard to temperature and, if adjusted slowly, will thrive in unheated aquariums. Many species breed readily in the aquarium.

Walking Catfish (Clarias batrachus)

The eel-like body, large size (up to 22 inches), and unique habits of this catfish endear it to those with an interest in unusual aquarium animals. Native to southeast Asia and India, walking catfish have established colonies in the southeastern United States since their introduction there as escaped pets in the 1960s. Because they are quite destructive to native aquatic animals, many places now prohibit their importation.

Olive green in color in the wild, captive strains of walking catfish are now available in albino and ones with gold and black flecks. They possess a well-developed auxiliary breathing organ and can thus survive for extended periods out of water. This, combined with their ability to “walk” upon their stout pectoral spines, enables this aptly named fish to travel over land when conditions deteriorate in the home environment. This ability has also thwarted efforts to control introduced populations in the United States; when poison is added to the pond, the catfish simply walk to another!

Like all catfish, walking catfish possess sharp pectoral and dorsal spines. In this species the venom injected by the spines produces a very painful wound. Handle only with a heavy-duty net.

Walking catfish are voracious feeders and soon become quite bold and willing to feed from the hand (watch your fingers!). Their appetites know no bounds, and they fare quite well on all manner of frozen, pelleted, and live foods. It is quite impossible to house any fish smaller than walking catfish in the same tank as walking catfish. A heavy hood on your aquarium is an absolute necessity, unless you want them walking about the house at night.

Saltwater Catfish (Plotosus lineatus)

This species, or a closely related family member, is the most commonly encountered marine catfish in the aquarium trade. Approximately one-third of the thirty or so species of its family inhabits marine or estuarine environments.

The saltwater catfish carries spines that inject a potent venom. These are located in front of the pectoral and dorsal fins. For this reason, these fish are best left to the care of professionals. The large (12 inches) adults can inflict a potentially deadly wound with their spines.

Saltwater catfish are one among several species of marine animals that can administer dangerous wounds with their venomous spines. The trade in most of these species is largely unregulated, so it is left to the hobbyist to use sound judgment with regard to such animals. With so many thousands of harmless species available, it really makes no sense to keep such animals in the home. They are included here as a matter of general interest, and for the reference of professionals.

The boldly striped young of the saltwater catfish travel about in schools and form a tight, writhing clump when disturbed. This behavior may deny potential predators a specific target, or it may confer upon the young the appearance of a much larger creature. The adults are fairly solitary and lose much of the juvenile coloration.

Saltwater catfish will accept a wide variety of animal-based foods and are especially fond of shellfish such as clams, mussels, and scallops. Spawning in the aquarium has, of yet, not been observed. Freshwater members of the family lay their eggs in a gravel nest that is guarded by the male, but it is not known if marine species exhibit this behavior as well.

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