Growth variability of morphometric characters in Perch fluviatilis and itsrelation to microhabitat use

Growth variability in 25 mensural characters was studied in 272 specimens o f Eurasian perch from Slovakia. Standard length (SL) of the specimens range d from 15.45 to 147.30 mm. Based on patterns of relative growth, three grou ps of mensural characters were found. Six characters were best explained by a linear regression, indicating isometric growth. Nine characters were bes t explained by a quadratic curve, indicating gradual allometry. The remaini ng 10 characters were best explained by a split-linear regression, indicati ng mainly isometric growth with abrupt allometry occurring at a specific SL (breakpoint). A shift in morphometric values (a transformation of the head and fin size and position, represented by nine characters) occurred at 29- 48 mm SL. Microhabitat use by perch in floodplain annexes of the River Danu be (Slovakia/Hungary) was then evaluated with respect to shifts in body mor phology at <29, 29-48, >49 mm SL using quantitative and semi-quantitative e nvironmental variables, as well as additional microhabitat data from Great Ouse (UK). The coincidence of morphological and ecological patterns in the development suggests changes in organism-to-environment relationships, i.e. ontogenetic thresholds. Transition from larva to juvenile period in perch appears to involve the 'metabiotic phase', i.e. a developmental interval be tween the acquisition/completion of adult structures and the stabilisation of relative growth.