A comparative survey of the type of sympathetic neuro-melanophore transmission in catfishes.

The types of innervation to integumental melanophores were surveyed comparatively within the order Siluriformes. In fish or many families, pigment aggregation within melanophores was found to be under the control of adrenergic sympathetic postganglionic fibers as in other fish. In silurid catfish, on the other hand, the cells were found to be regulated cholinergically, though the fibers concerned were sympathetic postganglionic. Muscarinic cholinoceptors mediate the melanin-aggregating response. In some catfish belonging to Bagridae, Pimelodidae and Callichthyidae, the melanophores strangely possessed cholinoceptors, notwithstanding the fact that they were under adrenergic nervous control. These results were discussed in conjunction with the phylogeny of Siluriformes.