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Pyxichromis orthostoma
by Greg Steeves

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As part of the Kyoga drainage system, Lake Nawampassa is home to an extraordinary piscivore, Pyxichromis orthostoma. Nawampassa is a shallow small lake less than a square kilometer in area. It is separated from the larger Lake Kyoga by a thin strip of rapidly diminishing swamp. Lake Nawampassa is the last refuge for a number of cichlids that once had a wider distribution within the Kyoga Basin. The wild population of P. orthostoma is considered severely threatened due to a fragile and shrinking habitat.

Fin Water Organism Fish Marine biology

The genus Pyxichromis contains three described species. P. paraothostoma (Greenwood, 1967) is found in Lake Victoria proper. P. paradoxus (Lippitsch & Kaufman, 2003) is native to Lake Edward, while P. orthostoma was originally discovered in Lake Salisbury, a tiny finger lake in the Kyoga system. This genus is distinguished by a small adult size, laterally compressed body structure and a protruding lower jaw slanted upwards. The large mouth is angled as well. The cranial profile is strongly concave. When compared with other piscavore lineages, the eye diameter of Pyxichromis is much smaller. The most obvious difference between P. orthostoma and P. paraorthostoma is the structure of the caudal fin. P. orthostoma has sharp angled corners whereas P. paraorthostoma has rounded corners. P. paradoxus has a lower body depth and differing dentition (bicuspid and tricuspid teeth) than displayed in P. orthostoma.

Fin Underwater Fish Marine biology Ray-finned fish

Female Pyxichromis orthostoma is unassumingly silver along the abdomen and lower jaw. The upper portions of the flanks and head are olive-green. The dorsal fin contains 14-15 hard rays and nine branched rays, while the anal fin has three hard rays and 8-9 branched rays. The 61-68 outer teeth are unicuspid, slender and pointed inward. There are two inner rows of similarly structured teeth. Male coloration can vary somewhat. Generally the male has a dull lime-green lower portion with a crimson-red coloration dorsally. The dorsal fin is powder-blue. The pectoral fins are jet-black. Posterior rays of the dorsal and branched rays of the caudal are red. There are two or three well developed ocelli dotting the rear portion of the anal fin. There is a lachrymal bar running from the corner of the mouth, through the eye and around the forehead. A black blotch is positioned mid flank in front of the caudal peduncle.

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