Sympatric Diversification of Dolly Varden Salvelinus malma (Salmonidae) in an Extremely Small Ecosystem

A planktivorous form of Salvelinus malma characterized by lacustrine winter spawning was discovered for the first time in north-east Asia in an isolated water system with an area of 0.23 km2. This form dwells in sympatry with the benthivorous form of the same species, which reproduces in autumn in the lake tributary. Given the size of the ecosystem, а single isolation event, and the absence of other fish species, this example of ecological diversification can be recognized as the simplest known in the world. The data on the growth rate, morphology, and feeding of two sympatric forms are presented.