Application of coded microtags to study growth rates of stocked sympatric whitefish (Coregonus lavaretus (L.)) forms

Five ecologically different whitefish forms were stocked in Lake Vuokalanja rvi in eastern Finland to establish dense populations and to analyse compet ition between different forms. Altogether, 213253 whitefish were tagged wit h coded wire tags (microtags) injected into their snouts in 1987-1988. The morphologically highly similar whitefish forms have different gill-raker co unt distributions, but distributions overlap. In 1989-1992, 12755 tagged wh itefish were recaptured and the codes of the microtags were identified. In this study a growth model was applied to analyse and compare growth rates o f different whitefish forms. The model was based on annual length increment s. Differences in both the length increments in the youngest age-group and also the annual decline in length increments of different forms were statis tically significant (F-test, p < 0.0001). Whitefish forms with dense gill-r akers had the greatest growth rates. (C) 1998 Elsevier Science B.V. All rig hts reserved.