Animal Plasticity and Environment

Abstract

WHILE recently making a zoological collection in the Sevoke River in the Teesta Valley at the base of the Darjiling Himalayas, I observed remarkable differences between the individuals of a Cobitid fish, Acanthophthalmus pangia (H. B.), collected from two diverse ‘niches’ in the same habitat. In Fig. 1 are shown the two types of individuals. The chief difference, which is readily noticeable in the two drawings, is that in the lower drawing the ventral fins are present, while in the upper these structures are totally absent. There are also other differences of a minor nature; for example, the extent of the nasal flap and the form of the caudal fin. Two specimens^* possessing ventral fins were obtained from among pebbles and shingle in a swift current, whereas 18 examples devoid of ventral fins were netted from among debris at the bottom of pools in the course of the stream.