Local differences in calretinin immunoreactivity in the optic tectum of the ocellated dragonet

•We studied the distribution of calretinin in the optic tectum of a bony fish.•The calretinin-immunoreactive cell bodies and fiber layers correlate with functional subdivisions of the optic tectum.•Calretinin-immunoreactivity can be used to reveal specializations of neuronal structures reflecting functional adaptations.

The optic tectum of the ocellated dragonet (Synchiropus ocellatus) was studied with immunohistochemistry. Antibodies raised against the calcium binding protein calretinin (CR) revealed a lamination similar to that already reported for other ray finned fish. Most immunoreactive fibers could be observed in those layers receiving retinal afferents and most immunoreactive cells occur in the stratum periventriculare. However, there are marked differences in the presence of other calretinin-positive cell types and immunoreactive lamina between the dorsomedial and ventrolateral parts of the tectum. Synchiropus is a bottom dwelling fish with strong functional subdivisions of the visual system into dorsal and lateral visual fields. The differences in calretinin-positive cell bodies and fibers may be a sensitive indicator of functional differences of tectal circuitry.