Effect of Spinal Lesions on the Colour Change of the Minnow (Phoxinus phoxinus L.)

Abstract

THE dorsal and lateral surfaces of the minnow (Phoxinus phoxinus L.) change colour on pale and dark backgrounds. This colour change is effected by changes in the condition of the melanophores which are found on these surfaces of the minnow. Large macromelanophores and small micromelanophores can be seen under the binocular microscope, and the differential distribution of these two types gives rise to a prominent pattern which is to be observed particularly during the paling and darkening of the fish. Black-adapted minnows taken from a black background and placed on a white one pale rapidly during the first few minutes under nervous control, then continue to pale at a slower rate under hormonal control¹—maximum pallor is reached after some hours. The macro-melanophore pattern pales more slowly than the micro-melanophores and it is still visible after the fish has been paling for one minute but has more or less disappeared after 3 min. On a black background the fish darkens rapidly during the first few minutes and maximum darkness is attained after some hours.