Big-eye cichlid, Acaronia nassa

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Matt Clarke looks at Acaronia nassa, an unusual cichlid from the Amazon basin.

Common name: Big-eye cichlid

Scientific name: Acaronia nassa Heckel 1840

Origin: Quite widespread across the Amazon basin. Museum specimens have been recorded from Venezuela, Peru, Bolivia, the Amazon and Rio Negro in Brazil, French Guiana and Guyana.

Size: Said to reach up to 25cm/10". However, I had three of these for a couple of years and mine only reached about 15cm/6" in length.

Diet: A predator that feeds on aquatic insect larvae and small fishes. It has a rather big mouth so don't keep it alongside anything too small. Mine happily accepted flakes, pellets and frozen foods.

Water: Varies according to collection locality, but those from the Negro are swimming around in extremely soft acidic water (pH 4, GH 0, KH 1 ish). However, this species is quite adaptable and does OK in harder water when properly acclimatised.

Aquarium: My own fish were kept in a 90cm/36" tank furnished with silver sand and bogwood and lived happily alongside some Geophagus proximus and Triportheus giant hatchets. Plenty of cover is needed in the tank, as males can be quite hard on females. I caught a couple of these fish while I was on the PFK Rio Negro Expedition last year. The fish were caught early in the morning in water a few feet deep on the edge of a very steeply sloping sandbank. The habitat was very bleak and consisted entirely of open sand, with no rocks, pebbles bits of wood or plants for hundreds of metres around. The water was extremely dark and peaty so the fish would have been used to living in very low light levels, which might explain the enormous eyes. Other fish caught alongside A. nassa included Mesonauta insignis and numerous small Hyphessobrycon upon which this species probably predates.

Identification: There's only one other described species of Acaronia, A. vultuosa, which is even rarer in the trade than nassa. The two fish have quite distinctive markings on the head and opercula that allow them to be told apart. A. vultuosa comes from the Orinoco drainage, where it lives alongside Uaru fernandezyepezi in the Atabapo, but also occurs alongside nassa in upper parts of the Negro.

Availability: These are not commonly seen in the shops and they don't appear to be particularly abundant in the wild. We spotted these recently at Wholesale Tropicals in London (0207 739 5356).

Price: Not common, so usually quite dear. These ones were a bit of a scoop at only 12.50 each.