Microhabitat use of a native New Zealand galaxiid fish, Galaxias fasciatus

To assess microhabitat selection by banded kokopu (Galaxias fasciatus), a total of 215 fish were observed using spotlight along 350 m of Sawyers Bay stream in southern New Zealand. We measured multiple microhabitat variables at the focal point position of each observed fish. A correlation analysis showed that depth, focal velocity, adjacent fastest velocity and substrate were the factors most strongly associated with the fish position. Our results showed that patch use by banded kokopu was clearly size-related. Small fish (≤90 mm) occupied shallow pools with fast velocities over fine substratum, whereas large fish (>90 mm) preferred deeper pools with slower water velocities and coarse substrates. We suggest that such microhabitat partitioning could be related to agonistic intra-specific interactions and a social hierarchy among individuals.