| Summary: | This report deals with life-history variation for Eurasian perch (Perca fluviatilis L.), with special emphasis on age and size at maturity in females, in perch populations that have changed in size distribution. The collection of fish samples was made with multimesh gill nets year 2011. The perch’s length, height, weight, status of gonads has been analyzed, and by observing the opercular bone the age has been determined. In two lakes close to Umeå in northern Sweden, Fisksjön and Ängersjön, the live-history traits of perch have been studied. Similar studies have been made year 2000 and that data will be compared with the result of this study. Gillnet fishing has shown that Fisksjön has changed population structure from a stunted population, many and small individuals of perch, to giant-phase, with fewer but larger individuals. As a comparison Ängersjön has also been studied, but there no structure change in population has occurred. It would be interesting to see if live-history traits now differ since the distribution of perch has changed in Fisksjön. The results show clearly that a change in perch size distribution has taken place. In Ängersjön no sign of change in population structure has been observed. The growth in Fisksjön has changed, with a stunted population the perch was shorter than it is in giant-phase at the same age. The opposite pattern was found in Ängersjön. Age at maturity occurred at a lower age during the stunted population phase than in giant phase. No difference in weight and length was observed. In Ängersjön the perch were shorter and lighter at maturity year 2011 than year 2000. No significant difference was observed in age at maturity in Ängersjön.
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