Length-weight relationship and condition factors of European perch, Perca fluviatilis, from 38 lakes in northeastern Poland

Length-weight relationships and condition factors of various fish species depend on food resources, habitat, season, water quality, and the size, age, and sexual maturity of fishes. The aim of this study was to determine the length-weight relationships (LWR) and the values of the Fulton condition factor (K_f), the allometric condition factor (K_a), and the relative condition factor (K_r) of European perch Perca fluvatilis from 38 lakes located in northeastern Poland. The total length (TL) of the perch ranged from 3.9 to 41.4 cm. The body weight of the fish caught ranged from 0.4 to 1,162.1 g. The linear regression coefficient of the LWR was highly significant (r²=0.99). Parameter b (3.1859) indicated positive allometric growth. The mean values of K_f (0.996 ± 0.154) and K_r (1.003 ± 0.121) indicated that the fish from the Polish lakes were in good condition. None of the condition coefficients differed significantly among the various maximum depth ranges of the lakes (P > 0.05). RDA analysis indicated a weak positive correlation between K_r and morphometric parameters of lakes. K_a was strongly correlated with lake surface area, while K_f was weakly correlated with the depth of the lakes studied. The results of this study are very important for updating data regarding the fish fauna of Polish lakes and for the management of commercial and recreational fisheries.