As a result of background response, the rate of colour change by exposure to a light (white) and dark (black) background under constant illumination has been described. For the measurement of response, Munsell Colour Index including (figs.3 and 4). The various grades representing body shade, was utilized. These grades were matched to the changes in body shade during adaptation to specific background by necked eye and it represents a subjective method. The results, obtained clearly indicate that the responses are biphasic where initial response is faster followed by a slow, gradual and prolonged colour change.

The data recorded clearly indicate the participation of both the nerves and hormone(s) during background responses. It appears that the responses are initiated neurally and cover a large part of colour change which at a later stage is supplemented by hormonal means. The fish requires 30 min for initial faster change in both the backgrounds and then it takes a time of about 5 hr to nearly complete the response. However, on leaving the fish overnight in the appropriate background, same more change in terms of Munsell grades has also been recorded. The maximum paling the fish attains on a white background is 8 Munsell Colour Index. While the maximum darkening equals the grade 2.5.Thus these grades represents the range to which the fish is capable of changing its colour.

The rate of colour changes as a result of adaptation to different backgrounds i.e., white and black do point for a biphasic control, where they appear to be initiated by neural control and completed by simultaneous and synergetic hormonal control in the fish.