The Fishes: Crenuchidae

CYPRINIFORMES - carps and characins: Page 2

Family: Crenuchidae

Family: Anostomidae

Crenuchidae
The composition of this family has recently been revised by Buckup (1998) who now places within it two monophyletic subfamilies: the Crenuchinae and the Characidiinae (formerly the Characidiidae). The family is characterized by skeletal structures within the head and the position of the optic nerve.

Crenuchinae
This subfamily comprises only two genera, Crenuchus and Poecilocharax. Crenuchus holds but a single species, the curious little fish C. spilurus, the sailfin tetra. Although a member of the Characiformes it has the superficial appearance and behaviour of a cichlid. Little is known about its behaviour or ecology. While never abundant it is occasionally caught in both white and blackwater floodplain lakes. The genus Poecilocharax has two species P. bovalii and P. weitzmani. Members of this genus lack adipose fins.

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Dorsal view of a preserved specimen of Crenuchus spilurus caught near Tefe, Brazil

Characidiinae
This subfamily includes the genera Amnocryptocharax, Characidium, Elachocharax, Geryichthys, Klausewitzia, Leptocharacidium, Melanocharacidium, Microcharacidium and Odontocharacidium. The taxonomy of this group has been reviewed by Buckup (1991, 1993). Characidium and Elachocharax are common genera of streams, leaf-litter banks and floating meadow, Most are small species with an adipose fin and cycloid scales.

Elachocharax pulcher
Identification: This genus is easily identified by colour and size. Background colour is chocolate brown broken by a number of irregular off-white vertical bars. Adult standard length is about 2 cm. The individuals captured from the Taruma-Mirim have been assigned to Elachocharax pulcher. There is a second species which looks similar, E. junki.
Habitat: Within litter banks. This species has never been observed in open water. When undisturbed, it moves over the surface of the leaves looking for prey. It is probably territorial or at least stays for extended periods within a small area. It favours litter bank areas with whole leaves and seems indifferent to depth.
Abundance: Very common. Average density throughout the litter banks of the Taruma Mirim was found to be 8.8 individuals per sq. m. Within favoured areas of litter densities can be higher, on average 33 individuals per sq. m.
Food: A general predator. It has a very small mouth so feeds on smaller invertebrates.
References:

Weitman & Gery (1980) Proc. Biol. Soc. Washington 93(4): 887-913.

Weitman (1986). Proc. Biol. Soc. Washington 99(4): 739-747.

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Elachocharax pulcher - Pair of adults caught in a litter bank in a blackwater stream	Elachocharax pulcher - Pair of adults caught in a litter bank in a blackwater stream

Characidium spp
Identification: All Characidium species have a characteristic cryptic coloration they are almost transparent with brown or black markings. Characidium sp 1 is the common Characidium in Tarumă-Mirim. It comes in two forms, one has black dots along the lateral line. The other has a complete line. They seem to differ in no other respect (male and female?). Characidium sp 2 & 3 are larger forms also found in forest streams.
Habitat: Within leaf-litter banks
Abundance: Characidium sp 1 is abundant, average density was 18.8 individuals per square meter of litter surface area. Maximum density was 60.
Food: Predators of micro-invertebrates.

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Lateral view of a Characidium species caught in submerged leaf litter	Lateral view of a Characidium species caught in submerged leaf litter	Lateral view of a Characidium species caught in submerged leaf litter	Dorsal and lateral views of a Characidium species caught in submerged leaf litter	Dorsal and lateral views of a Characidium species caught in submerged leaf litter

Anostomidae
A widely distributed South American family of characiform fish which are particularly common in floodplain lakes. They are often torpedo-shaped fish with small heads and terminal mouths. Most species are relatively small. They feed on both plants and invertebrates and are noted headstanders. Many species display longitudinal stripes. Typical species in Amazonian lakes are Abramites hypselonotus, Anostomus taeniatus, Anostomus trimaculatus, Leporinus fasciatus, Leporinus friderici, Rhytiodus microlepsis and Schizodon fasciatum

Abramites hypselonotus
This is an abundant species of white water floating meadow where it feeds on plants and tiny invertebrates. It uses the headstanding position when feeding.

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Abramites hypselonotus - Lateral view of preserved specimen caught in floating meadow in an upper Amazonian floodplain lake near Tefe

Anostomus taeniatus
An abundant species in protected habitats such as floating meadows where it feeds on tiny crustaceans and insects.

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Anostomus taeniatus - Live specimen caught in floating meadow in Lago Mamiraua

Anostomus trimaculatus
A common anostomid of floating meadow. The name is derived from the three black marks on each side and the common name is three-spot anostomus. The maximum length is about 20 cm. While other species may be numerically more numerous this species makes a high contribution to the floating meadow animal biomass. It feeds on small animals and vegetation.

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Anostomus trimaculatus - Lateral view of preserved specimen caught in Lago Mamiraua, near Tefe

Leporinus fasciatus
Called the banded leporinus on account of the alternating yellow and black vertical bands along the body, this is the most popular anostomid with aquarists. They are common amongst floating meadow, where they feed by grazing on algae and plants. The maximum length is about 30 cm.

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Lateral view of a freshly caught specimen of Leporinus fasciatus from a white water floating meadow showing the natural colouration	Lateral view of a preserved specimen of Leporinus fasciatus caught in a white water floodplain lake near Tefe

Leporinus friderici
A common anostimid of floodplain floating meadows. It is known to feed on plants and prawns and probably is a general scavenger.

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Leporinus friderici - Lateral view of a specimen freshly caught from a white water floating meadow near Tefe

Rhytiodus microlepsis
This anostimid lives within floating meadow and other sheltered habitats within the floodplain lakes. It is well camouflaged and shy, although when disturbed it moves with great speed.

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Painting of an adult Rhytiodus microlepsis made by Peter Henderson in the field from a freshly caught specimen, showing the natural coloration

Schizodon fasciatum
This is one of the most abundant anostomids of white water floodplain lakes and is easily recognized by the characteristic dark barring pattern along the sides of the body. It is a general scavenger and herbivore which will take small invertebrates when given the opportunity.

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Lateral view of preserved specimen of Schizodon fasciatum still showing the characteristic dark markings. This species is abundant in floating meadow	Painting of an adult Schizodon fasciatum made by Peter Henderson in the field from a freshly caught specimen showing the natural coloration.