Matt Clarke looks at Brittanichthys axelrodi, an unusual characiform fish from the Rio Negro basin.
Scientific name: Brittanichthys axelrodi, Gery, 1965
Origin: Rio Negro basin, Brazil and Colombia South America. The type specimens were caught in the Rio Itu at Praya Bulufu about 80k/50 miles upstream of the middle Rio Negro. Other specimens have been caught near the Rio Urubani, a Rio Negro tributary, the Rio Demini, and the Rio Muco in Vichada, Colombia.
Size: Less than 3cm/1.2.
Diet: No data available, but, like other small characids, plankton, insects and detritus are likely to form part of the diet. Those I've kept in the past have been shy and did not immediately accept dried foods, so offer some small frozen foods, such as Cyclops and Daphnia, while they're settling in.
Water: The blackwaters of the Rio Negro are very soft and acidic, often virtually devoid of hardness with a pH of 4.0 or less. These should ideally be kept only in very soft and acidic water. Mine were OK at pH 6.
Aquarium: This is a rather fragile shoaling fish and should be kept in a large group in a tank containing only other small placid species. Mine were very nervous and fared best when kept alone in a densely planted aquarium, so they're unlikely to do well in the average community tank. Males can be quarrelsome with their own kind at times.
Notes: This species is one of two members of the genus, both of which were described by Jacques Gery in 1965. The other one is called B. myersi. They're currently considered a member of the family Characidae, but are classed by taxonomists as incertae sedis, which means that their real taxonomic position is uncertain. B. myersi appeared in imports last year via Germany wholesaler Aquarium Glaser.
Sexing: Males inseminate females with sperm, rather than fertilising eggs externally like most tetras. Mature males have bony hooks on the fourth unbranched ray and branched rays 1-4 of the anal fin. Males also have a curved caudal fin when adult, as well as brighter coloration. There don't appear to be any reports of successful spawnings of either Brittanichthys species.
Identification: I've been unable to track down original descriptions for myersi and axelrodi so cannot provide details on telling the two species apart or confirm that the fish shown are definitely axelrodi and not myersi.
Availability: This is not commonly seen in the hobby. We spotted these at Coxwell Aquatics. They are not particularly attractive fish, having a certain weatherbeaten look. Once established, the red stripe on the caudal peduncle should be much more striking.
Price: On sale for 8.95 each.
This article was first published in the September 2008 issue of Practical Fishkeeping. It may not be reproduced without written permission.