Matt Clarke on the rare Astatheros rhytisma.
Scientific name:Astatheros rhytisma
Origin:Found in the Rio Sixaola on the Atlantic slope of Costa Rica, Central America. Some claim that the range may extend to the nearby Rio Guaromo and the Rio Calovebora in Panama, others think these are misidentifications.
Size:Adults reach 18cm/7" and get quite stocky with a silvery base colour, heavy head and blue squiggles on the operculum. They look like a rather chunky cross between an alfari and an Aequidans pulcher - very different to juveniles.
Aquarium:This species is found in moderate - or fast-flowing water about 40-60m above sea-level in the main Rio Sixaola and in attached streams, so provide a ecent flow. A large (227 l./50 gal. approx) tank decorated with silver sand, river-worn boulders and pebbles suit these well, and allow them to sift for food naturally.
Diet:Wild fish feed on vegetable matter, insects and detritus.
Breeding:Open spawners who are aggressive during reproduction. Provide females with shelter and be prepared to remove them, and raise the brood artificially, if disputes break out.
Notes:Described by Lopez in 1983, and a member of the alfari group, which includes A.alfari, A.bussingi, A.diquis and A.rhytisma, which (apart from alfari) exist mainly on the Atlantic side of the region. Many are found way above sea-level.
Availability:These rarities were spotted at Wholesale Tropicals and Bethnal Green, London. We've heard that both wild and tank-bred rhytisma have arrived in the UK recently.