Correspondence between ontogenetic shifts in morphology and habitat use inminnow Phoxinus phoxinus

The morphology of minnows Phoxinus phoxinus from two rivers at the south-ea st of England was analysed on mensural characters and qualitative traits (o ccurrence of appendages, pattern of pigmentation and scalation). Eight deve lopmental intervals were identified from the qualitative traits, and bivari ate and multivariate analysis revealed that allometric growth occurs occasi onally during ontogeny, mainly in earlier developmental periods. Body shape is under the influence of rapid increase during development, mainly due to the quick growth in early developmental intervals. The exclusion of 'gener al size', remarkable in early developmental intervals, revealed several 'sh ape' characters that mainly determine minnow morphology by changing the mod e of variability during development (e.g. caudal characters, maximum body h eight, belly length and ventral head length). The tail certainly undergoes the most consistent and most durable change, its characters being the most variable and the most discriminative for developmental periods from larvae to adults. The most prominent alteration in the overall shape development o ccurs at the transition from larva to juvenile, both regarding the number o f characters involved into the change and their variability. This transitio n takes place at about 28 mm SL, which corresponds to a significant change in microhabitat use in both the rivers Lee and Frome, characterized by shif ts by 0+ juveniles to significantly deeper waters than those occupied by la rvae, with increased amounts of either submerged filamentous algae (Lee) or vegetation (Frome).