Microhabitat use by the larvae of cryptic lamprey species in Lethenteron reissneri in a sympatric area

Microhabitat use by the larvae of two cryptic lamprey species in Lethenteron reissneri, Lethenteron sp. N (northern form) and Lethenteron sp. S (southern form) larvae, as well as intraspecific variations on a size-related basis, were examined in a study area (500 x 5m) located on a stream where they showed sympatric distribution. The total number of individuals collected from each of 31 quadrats (60 x 60 cm) ranged from 0 (0n/m(2)) to 13 (36.1n/m(2)). The distinct difference in habitat use was not observed between the two species in the present study area. Lamprey density was not significantly independent among the size groups (small and large) for each of Lethenteron sp. N and Lethenteron sp. S. The density of each size group of the two species was significantly correlated with some habitat variables, and stepwise multiple regression analysis revealed a positive association for a substrate with a smaller particle size and deeper depth for large individuals of Lethenteron sp. N and Lethenteron sp. S, respectively, suggesting that these conditions would be suitable for burrowing. On the other hand, small individuals of both species tended to occur in areas where there was a high content of medium sand and a faster current velocity, probably reflecting a preference for respiratory efficiency. Various condition of habitat should be maintained to conserve the cryptic lampreys.