Diet, growth and competitive abilities of sympatric whitefish forms in a dense introduced population: results of a stocking experiment

The food of five whitefish stocks Coregonus lavaretus planted in Lake Vuokalanjärvi consisted mainly of zooplankton and insects taken from the water surface. The amount of benthic food in the diet of the two sparsely gill‐rakered (23 and 28 rakers) stocks increased from the age of 2 years onwards. The growth of whitefish was slow in all stocks. The densely gill‐rakered stock (50–51 rakers) originating from the same lake system as Lake Vuokalanjärvi grew faster than the other stocks, and the food consumption of 4‐ and 5‐year‐old fish belonging to this stock was nearly double compared with the other stocks. The habitat choice of the whitefish differed between the stocks even in the densely‐rakered stocks classified as the same form. A stock with flexible habitat use and feeding habits is most likely to succeed. Introducing whitefish stocks from distant areas is not advisable.