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A visitor to any aquarium shop at the weekend is likely to encounter a wide range of the populace marvelling over the flashy little fishes glinting around the tanks like multicoloured jewels. Few will take the time to examine the bottom of the tanks, and if they do their eyes pass swiftly over what appears to be piles of detritus at the bottom. This is where banjo catfishes are to be found (assuming the shop even bothers to stock them), and while the fishes in the upper reaches are undeniably more beautiful, the fish lurking at the bottom hold a fascination for those who take the time to get to know them.
Banjo catfishes gain their common name from a passing similarity to a banjo in shape, albeit one made out bits of dead leaf. The body is flattened, and roundish in shape, followed by an extremely long tail that is the ‘neck’ of the banjo. There any resemblance stops – musicality is not one of their many interesting features, although like many catfish some species can make noises when perturbed using their pectoral spines and swim bladder.
Identifying which particular banjo catfish you are looking at is not the easiest of tasks, and can fool even experts. Although about 60 members of the Aspredinidae have been described, a large number of these are now considered merely to be forms of already described species. There are currently about thirty-five accepted species, but probably still more yet to be described! They vary greatly in size, from the tiny Ecuadorian Hoplomyzon papillatus, achieving the unassuming length of about 20mm, to the considerably larger Aspredo aspredo, which grows to over a foot long. Size is quite an important consideration when introducing one of these to your tank. Not only do you have to consider the space that the fish will actually fit into, but the size of the fish’s mouth! The banjo catfishes can eat amazingly large pieces of food for their size, and, as is usual for fishes with a short digestive tract, they are predators. Lurking at the bottom of the tank, immobile for the most part, and often semi-submerged in the substrate, they may look harmless, but are unlikely to look so harmless to a small fish investigating the bottom who has just witnessed an immense maw open in front of him. A commonly available banjo, Chaca chaca, the squarehead catfish, is particularly well known for quietly devouring small fish in the tanks of unsuspecting aquarists. This fish is also known as the ‘angler catfish’, and although the concept that they might lure small prey to them by angling with their barbels is a good idea, there seems little evidence. It is quite sufficient for them to lie in wait quietly until a small fish approaches, and then open their mouths wide. Water is expelled through the gills creating a vacuum, which sucks the unsuspecting prey in to its doom. Species tanks, or at least those with larger tank mates, are a good idea for these fish, although fish that can be relied upon to remain in the upper water layers are relatively safe. In the aquarium they can be kept happy with large quantities of live or frozen bloodworm, tubifex and other sinking meat foods, on which they will gorge themselves thoroughly.
This family of catfishes has a number of remarkable features. Although not one of the mailed catfish groups, the head is shielded by a bony shield that is visible through the skin and gives them a mailed appearance. The skin itself is completely keratinised and ornamented with tubercles, and is shed periodically, like that of a snake. They are marked to allow them to be as unobtrusive as possible, with ‘dead leaf’ patterns in varying shades of brown. These patterns can be different between individuals of the same species, and the effect, coupled with bumps and knobs on the heads and bodies of some species, make them almost indistinguishable from the vegetation and leaf litter of their native South American streams. They are so good at staying still that some specimens have been found in the wild almost entirely surrounded by sheets of algae, that must have taken some time to grow. Nonetheless they are indeed capable of movement, and can not only swim by undulating their bodies but also by squirting jets of water from their opercular openings, moving along the substrate by jet propulsion.
Although many fishes practise parental care, often guarding their eggs with great diligence, there are few that carry their eggs around with them. One group of the banjos, including the genera Aspredo, Aspredinichthys, and Pterobunocephalus care for their eggs by attaching them to their bodies. While in Pterobunocephalus the eggs are directly attached to the body, the others have their eggs joined on by fleshy stalks. These grow out from the female in the spawning season, and may allow interchange of nutrients between the mother and the developing fry. These stalks, known as cotylephores, remain on the female after the fry have hatched and become free-swimming. It has been suggested that the eggs are attached in this way in order to be carried from brackish spawning sites into freshwater for the fry to hatch, although little is known for sure on the subject. Aspredo cotylephorus (named for the egg stalks) is reported to have spawned in aquaria, and it has been theorised that the females lay their eggs in a hollow depression and then lie on them when they become joined to the cotylephores. It is suggested that the fish actually spawn in brackish water and then migrate against the current into fresh water, carrying their eggs with them to an environment where the fry can hatch safely. A female imported with eggs already on the belly by Dr. David Sands resulted in the successful hatching of fry in fresh water, after which the female, who had been ignoring food, returned to her normal voracious feeding habits.
Bunocephalus do not carry their eggs around, but have been known to spawn in the aquarium. Usually in the Spring, after the fishes have been well-fed for several months, the male chooses a spawning site and excavates a hollow, wherein the female deposits a large number of eggs – between 4,000 and 5,000. The male guards the eggs until they hatch, when they can be fed on microworms and rotifers before graduating to larger live foods. This fish, known as the ‘little guitar’ in parts of South America, is relatively often available in shops, and will give even the experienced aquarist a new challenge in spawning, as indeed will all the banjo catfishes.
Although these fishes have been found in aquarists tanks for some time, their habits remain largely un-investigated and unknown. The fish pretending to be a pile of rubbish on the tank bottom offers one of the best opportunities around today for an aquarist to try something new, observe, and return information to the hobby, and deserves a closer look next time you are in the shop being dazzled by the fast swimming beauties in the upper reaches!
This article has been kindly provided by Kathy Jinkings and cannot be reproduced without her permission.
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