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Introduction

The Aspredinidae are known as banjo catfishes due to their overall body shape, a depressed head and slender caudal peduncle which somewhat resembles a banjo. They occur throughout the tropical rivers of South America. Local names for aspredinids include "banjaman" or "banjo-man" (Guyana), "croncron" (French Guiana), "rabeca" (Brazil), and "guitarillo" (Venezuela). Banjo catfishes maybe found in habitats ranging from shallow backwaters to deep river channels to tidal estuaries. In general, most species are cryptically pigmented, benthic and sluggish unless disturbed. Many are semi-fossorial, during the day often resting just beneath the substrate surface.

Approximately 6O extant species of banjo catfishes have been described. A large proportion of these species are now considered subjective junior synonyms of earlier described species. As currently recognized the family contains approximately 35 nominal species placed in 13 genera. In addition there are several undescribed species mostly in the genus Bunocephalus. Despite the relatively small number of species in this family as compared to other catfish families, aspredinids are quite diverse in their morphology. They range from miniature armored species such as Hoplomyzon papillatus, less than 20 mm in length, to large elongate species such as Aspredo aspredo, reaching up to 380 mm in length.

Aspredinids are a highly derived group of catfishes and display some very unusual features. Their skin is completely keratinized and covered with tubercles. Periodically the entire outer layer of skin is shed just like that of amphibians and reptiles (Friel, 1989).

This SEM micrograph shows rows of enlarged tubercles which run longitudinally along the bodies of aspredinids. The light spots covering the tubercles are unicellular keratinized processes called unculi (Roberts, 1982). The horizontal field of view of this image is 1.68 mm.

While aspredinids can swim by typical undulatory movements, they can also use jets of water thrust from their opercular openings to skip along the substrate. When agitated, some species produce audible stridulatory sounds by repeatedly abducting and adducting their pectoral spines.

Very little is known about the general ecology of aspredinids. Based on little published work and personal observation, most aspredinids appear to be generalized omnivores and their stomachs often contain aquatic invertebrates, terrestrial insects and organic debris. One notable exception are members of the genus Amaralia. Based on stomach contents they appear to feed on the eggs of other catfishes (Friel, 1992).

Few specifics are known about reproduction of aspredinids. Parental care is known with certainty in one clade which contains Pterobunocephalus, Platystacus, Aspredo, and Aspredinichthys. Females of this clade carry their developing embryos attached to the ventral surface of their bodies. In Pterobunocephalus, the eggs are directly attached to the body whereas in Platystacus, Aspredo, and Aspredinichthys they are attached to fleshy stalks, called cotylephores, which grow out from the female (Friel, 1994). These develop seasonally and may function in the exchange of materials between the mother and her developing embryos (Wetzel, Wourms, & Friel, 1997).

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