Life history of roach, Rutilus rutilus (Cyprinidae, Teleostei). A qualitative and quantitative study on the development of sensory brain areas.

The present study deals with aspects of the brain development in the roach, Rutilus rutilus, a common mid-European cyprinid fish. The morphogenesis of selected brain areas from hatching to early juveniles was examined on serial paraffin cross-sections. From early juveniles to large adults, brain growth was quantitatively analyzed by computer-aided planimetry. The hatchlings of roach show a cytologically distinct optic tectum, but a poorly differentiated brainstem, reflecting the predominance of the optic sense during the larval planktivorous period. The differentiation and outgrowth of chemosensory brainstem centers is related to the onset and development of benthivorous feeding in juveniles. The optic tectum decreases in size relative to the total brain volume from juveniles through adults. The corpus cerebelli increases in relative size, whereas chemosensory and acousticolateral centers grow isometrically with the brain as a whole.