The influence of water depth on growth rate and size of the Japanese endemic crayfish, Cambaroides japonicus, was examined in both the laboratory and the field. The growth rates of individuals reared at different depths (10, 50, 100mm) were investigated for 5 months, from stage II initially to stage VII or VIII at the end of the study. This experiment clearly showed that the growth rates of individuals were affected by water depth, shallow individuals growing more slowly. Crayfish were collected from 28 brooks and 6 lakes throughout the Shiribeshi district, Hokkaido, Japan, and their sizes were compared. Analysis of variance indicated that crayfish collected from lakes (i. e. deeper habitats) were larger than those from brooks.