| Summary: | 1. This paper is a revision, in the light of newevidence, of an earlier one (Svärdson 1957) on the same subject. 2. The biological species concept is adopted. Lake Locknesjön, headwater of the Gimånriver, is inhabited by three indigenous species. The large sparsely-rakered whitefish has 19 gill rakers, the lesser sparsely-rakered whitefish 22 and the southern densely-rakered whitefish 42 rakers. Their ecology is different. Experiments show that the morphological as well as the ecological traits are mostly genetically based. 3. The river whitefish with about 30 gillrakers is a fourth Scandinavian species. Normally it runs the lower parts of the rivers. It was introduced in Lake Lockne sjön in the 1940s and from Lake Vänern to upperlakes of the Indalsälven river system in 1870. If it lived allopatrically it was not changed, but if it lived sympatrically with native species introgression have occurred. In Lake Vänern it lives, spontaneously, sympatrically with both large and lesser sparsely rakered whitefish. The alleged evolution of a new species in postglacial times (Svärdson 1970) was based on introduced fish whose origin was mistaken. 4. The northern densely-rakered whitefish is a fifth species. In Lake Storvindeln it has more than 60 gill rakers and is close to the “riverpeled” of north-western U.S.S.R. It grades by introgression to some 45 rakers in other lakes but proves its specific rank by living sympatrically with all the other forms. 5. The blue whitefish, with 30—35 gill rakers, is the sixth and most competitive species. It has a tendency to oust the southern densely-rakered species as well as the lesser sparsely-rakered one. Its specific status is proved by sympatric coexistence with all the other forms in several lakes. 6. There are five sympatric whitefish species in Lake Vänern as well as in the Arjeplog lakes of the Skellefte river. Two species live in the Baltic Sea. 7. The order of postglacial arrival from the Ancylus Lake could be studied in lakes of the upper Ljusnan river and a complex ...
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