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his month (April 2015) we are concentrating on a little known family, in the aquarium trade anyway, and that is the Cetopsidae. When you think of this family you think right away of the candiru and other parasite catfish which can be nasty but H. marmorates is very different to this behaviour and is recomended in groups in an aquarium.

Helogenes marmoratus

A little bit of history on this species and three others in the Helogenes genera, H. castaneus (from the Rio Meta basin, Colombia) H. gouldingi, (from the Rio Madeira basin, Brazil) and H. uruyensis from southern Venezuela. They were all in the previously named Helogenidae family but were incorporated into the Cetopsidae family in 1995 and consequently in the sub-family Helogeninae. H. marmoratus although scarce in the hobby seems to be the only one out of the four species that is sometimes exported from the trade.

When Günther described H. marmoratus in 1863 he placed it in the Hypophthalmidae and it was not until 45 years later that Eigenmann on its second collection that he removed Helegenes from Hypophthalmidae and described a new family for it, the Helogeneidae. The species remained monotypic for a further nearly 80 years until Delsman described a second species, H. amazonae based on a single species caught in the vicinity of Manaus, Brazil, this turned out later to be a synonym of H. marmoratus. Another species was named by Dahl in 1960 and naming it Leyvaichthys castaneus. This later was renamed Helegens castaneus and the main discription was the lack of an adipose fin, hence the new genus name. This variability within the Helogenidae concerning the adipose fin which ranged from the Peruvian populations from relatively small, through very small, to being totally absent and this absence of the fin had been used to distinguish, wholly or in part, the genus Leyvaichthys from Helegenes.

The possession of nine principal fin rays in the lower lobe of the caudal fin of Helogenes marmoratus distinguishes it from H. gouldingi and H. castaneus, which have eight principal rays on the lower lobe of that fin. The 39-48 anal-fin rays of H. marmoratus separates that species from H. uruyensis, which has 32-37 anal-fin rays.

Helogenes marmoratus

H. marmoratus is a typical inhabitant of black or clear waters, and is usually found in forest streams with a moderate to swift current flow over firm sand or gravel bottoms. Lives hidden under plants, litter or plant debris. Can easily be mistaken as a piece of dead wood when it rests on its side, and lies motionless on the bottom. Often swims on one side in undulating movements.

This is a catfish that likes the upper levels of the aquarium. It likes to hide in plants/vegetation at the surface so either floating plants or long strands of Valisineria plants would work better as they will be unhappy in a bare unplanted tank. This trait can be seen in the upper image.

Dwarf Wood Cat

Helogenes amazonae, Helogenes unidorsalis

Helogeninae

South America: Atlantic drainages of Guianas, upper Orinoco and Negro systems and upper Amazon River basin. Madre de Dios region, Peru. Type locality: Essequibo River, Guiana.

7.5cm. (3ins)

22-26°c (71-79°f )

Nine principal fin rays in the lower lobe of the caudal fin. 39-48 anal-fin rays. Dorsal fin small and set well back, anal fin long. Adipose fin is is very small sometimes lacking, dorsal and pectoral fins without spines. Eyes are small, directed upward and outward. The maxillary barbels fit into a groove below the eye.

A nocturnal species that needs plant cover to rest in during daylight hours. Does not like too much of a water movement in the aquarium. Can be kept with a vast variety of peaceful fish as long as they are not too small, but would be better to keep at least six specimens of this small species in a tank of their own.

Not recorded.

In its natural habitat it feeds mainly on terrestrial insects, particularly ants. In the aquarium it will eat most aquarium prepared foods, small live foods, insect larvae and small worms. Feed prior to turning of the tank lights if housed with other species.

Adipose fin: Fleshy finlike projection without rays, behind the rayed dorsal fin.
Anal fin: The median, unpaired, ventrally located fin that lies behind the anus, usually on the posterior half of the fish.
Dorsal: The primary rayed fin(s) on top of the body.
Caudal fin: The tail.
Maxillary barbels: Pertaining to the upper jaw. (maxillary barbels)
Pectoral fin: The paired fins just behind the head.
Ventral Fin: The paired fins, between the pectorals and the anal fins.

Helogenes: Helos = marsh; genus = born.
marmoratus: Marbled; mottled.

Photo Credits

Top:  © Yann Fulliquet
Bottom: © Billy Grant