Identification of perch (Perca fluviatilis), pikeperch (Stizostedion lucioperca) and ruffe (Gymnocephalus cernuus) larvae

A quick way to distinguish between percids at the early yolk sac stage is to count the myomeres from yolk to anus, 2 to 3 for ruffe, 4 to 6 for perch and 7 to 9 for pikeperch. Reliable identification of later larvae involves more laborious myomere counting. Ruffe has only 13 to 16 preanal myomeres whereas perch and pikeperch have at least 17. The number of postanal myomeres is higher in pikeperch (27-31) than in perch (23-26) and ruffe (22-24). Tn perch less than 15 to 20 mm in size, the most useful feature is the characteristic line-shaped melanophore pattern between the myomeres. The melanophores may, however, be weak or lacking in perch from turbid waters, and in clear waters thin melanophores may also exist in pikeperch. The position of the mouth and the length of jaws can be used for identifying percids after they have attained a total length of 12 mm The number of fin rays in the anal and second dorsal fin can be counted by the time the fish are 16-18 mm in size.