Differential Growth in the Brain of the Weakly Electric Fish, Apteronotus leptorhynchus (Gymnotiformes), during Ontogenesis

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Abstract
Growth characteristics of the total brain and of several individual brain regions are described in Apteronotus leptorhynchus. The increase of brain volume relative to total length growth results in a sigmoid growth curve, in which three phases.sbd.proportional growth, positive-allometric and negative-allometric growth.sbd.could be distinguished. This type of enlargement of the total brain is due to the differential volume increase of individual brain regions and to the increase in the volume of the rhombencephalic structures in particular. Pros- and mesencephalic regions mainly grow in accordance with the overall enlargement of the total brain throughout development, whereas rhombencephalic and certain nuclear structures show such isometric growth only with the onset of the juvenile period. The results are interpreted in the view of functionality of the individual brain regions.