Environmental factors affecting the preference of branch drainage ditches by round crucian carp (Carassius auratus grandoculis), a Lake Biwa endemic subspecies, were analyzed, fish often ascending to paddy fields, via drainage ditches, for spawning. A logistic regression analysis to determine facors influencing, drainage ditch selection showed dissolved oxygen to be significant, whereas turbidity and water velocity were not. Nevertheless, differences in distribution between ditches selected or not selected for spawning suggested that greater water velocity and moderate turbidity were also important factors.
