Studies on the colour-change mechanism in a fresh-water teleost, Nandus nandus (Ham.). I. Neural control.

The existence and nature of chromatic fibres controlling the colour-change mechanism in the teleost, Nandus nandus has been studied by means of spinal sectioning at various vertebral levels of the animal between vertebrae 3 to 10. Spinal sectioning at or anterior to 5th vertebra completely eliminated the neural control of colour-change. As a result, the animal darkened to its maximum and the neural responses of different backgrounds were abolished. Spinal sectioning at or posterior to vertebra 6 did not affect the melanophores and at the same time did not interfere with the normal background responses of the animal. This study clearly shows that the chromatic fibres in this species run in the spinal cord and leave the latter at 5/6th vertebral level. Effect of adrenaline in the chromatic spinal-sectioned fish shows that the fibres innervating the melanophores are aggregating in nature and adrenergic in character. The results also suggest that the dispersed condition of pigment in the melanophores represents the "resting state" of the melanophores when they are under no stimulation.