colour and body shape. Local extirpation has made it impossible to further verify these data. Individually variable features of the morphology include the presence or absence of a black spot on the first dorsal fin, and the presence or absence of scales on the opercula, as well as the position and number of mucus glands on the head. Distribution FishBase reports only that the Balkhash perch is found in Lake Balkhash and Lake Alakol, both in Kazakhstan. N. S. Mamilov, a zoologist working in Kazakhstan, has described it as endemic to "the Balkhash lake watershed, including the Alakol Lakes system", and has mapped the presence and absence of the species in various rivers and other water bodies in that area. Maurice Kottelat, in his 1996 IUCN assessment states that the species' range also extends into parts of this catchment area that are in China, though no data on such populations were available. The Balkhash perch was introduced into the Nura and the Chu rivers, but in neither case was this a success. Fisheries Historically the Balkhash perch was a food fish that provided economically important, and sometimes dominant, fisheries. It constituted one third of the volume of the commercial catch in Lake Balkash, and two thirds in the Alakol Lakes system, in the 1930s and 1940s. Conservation status In assessments from 1986 to 1994, the IUCN Redlist status of the Balkhash perch was already assessed as 'rare'. The 1996 assessment noted that the population had declined and noted that this decline was blamed on the introduction of bream and predatory species, such as the Volga pikeperch (Sander volgensis). The population trend was described as 'unknown' and the overall assessment was that the species was data deficient. Mamilov wrote in 2015 that "Although the external morphology and life strategy of the Balkash perch appear rather adaptable, the species' future is uncertain." References Sources Mamilov, N.S., Biology of Balkhash Perch (Perca schrenkii Kessler, 1874). Chapter 3 in Perch Fish of Central Asia Freshwater fish of China Taxa named by Karl Kessler Fish described in 1874 Lake fish of Asia Lake Balkhash