Callichthys callichthys

Taxonomy

It was originally described as Silurus callichthys by Linnaeus in 1758. It is likely to represent a species complex.

Distribution

C. callichthys is distributed in all major river drainages of South America. It is very wide ranging, extending from Trinidad to Buenos Aires, Argentina, including the upper Amazon River and Paraguay River systems.

Description

The fish will grow in length up to eight inches (20 centimeters). The females are larger and more robust, and are a dull olive-green, while the males are brighter in color, exhibiting a delicate blue or violet sheen laterally, with a more developed and longer pectoral fin spine that is reddish-brown and edged with orange or reddish-orange.

Ecology

It lives in a variety of water types, from anoxic conditions (slack water zones surrounded by dense vegetation) to slightly turbid, but free-flowing, streams. It can be found in waters with pH range of 5.8 to 8.3, a water hardness of 0–30dGH, and a temperature range of 64–83 °F (18–28 °C). When its biotype becomes dry, it can move out of the water, due to its ability to swallow air and use its intestines to absorb oxygen from the atmosphere, to find more water.

It feeds at night on fish, insects, and plant matter. Juveniles feed on rotifers, in addition to the microcrustaceans and aquatic insect larvae they find when digging into the substrate.

During reproduction, the male's belly turns orange and its pectoral spines become longer and thicker. The male builds a bubble nest with some floating plants, fiercely guarding it after the female lays down her eggs.

Relationship to humans

The cascarudo is of commercial importance in the aquarium trade industry and of minor importance as a food source. It can be kept in aquariums, with groups of more than five individuals recommended.

In captivity

In the aquarium, these fish attain a length of up to 14 cm (5.5 inches). It is a peaceful and relatively undemanding species, usually active in dim light or at night, but hiding when the light is bright. It is an excellent jumper and the tank should be well-covered. They require at least a 20-gallon tank, although the water should be fairly shallow (6 inches or less), especially for breeding. Part of the reason for this is their habit of gulping air from the surface. The bottom material should be fine and dark in color. Plants should be strong and well-rooted. Floating plants can be used to keep the light level down and for breeding.

A temperature range of 24 °C to 26 °C is adequate, although for brief periods temperatures as low as 18 °C can be tolerated. The water chemistry is not critical but the water should be kept clean despite the fish's habit of stirring up the bottom.

It is easy to feed and will accept almost anything, both animal and vegetable, although it prefers live foods. Although it is primarily a bottom forager, it will include small fishes in its diet, probably taking them at night while they sleep.

Spawning has been accomplished in the aquarium and this fish is being bred commercially, although not in large quantities. Callichthys is a builder of bubblenests from plant parts, some bottom materials, and bubbles formed by a mouth secretion and air. The male forms a mass of bubbles about 20 cm (8 in.) in diameter and 10 cm (4 in) high. During the time of construction, the female is actively chased away or ignored. When the nest construction is complete, the male will accept the female. The eggs (up to several hundred) are deposited into the nest and the male or the pair will actively protect the nest for about four weeks until the fry come out of the nest at the size of 2.5 cm (1 in.).