Occurrence and distribution of freshwater shrimp in the Isazu and Yura Rivers, Kyoto, western Japan

Abstract

Seasonal occurrence and longitudinal distribution patterns of freshwater shrimp were investigated in two rivers in western Japan. Four species of the family Atyidae and two species of Palaemonidae were observed. Water temperature and life cycle patterns of these shrimps affected their seasonal occurrence. The amphidromous shrimp species Caridina leucosticta, Caridina serratirostris, and Macrobrachium nipponense were distributed within a brackish estuary and the lower reaches of rivers, while the landlocked shrimp species Paratya improvisa, Neocaridina denticulata, and Palaemon paucidens were found in the lower and middle reaches. The biomass of all shrimp in each sampling area measured between December and March ranged from 0.49 to 34.72 gm^-1 (wet weight in grams per meter of river bank) in the Isazu River with relatively dense riverbank vegetation, and from 0.06 to 1.22 g m^-1 in the Yura River with less riparian vegetation. Environmental factors such as stream gradient, distance to saltwater intrusion, structure of riverbank habitat, and the life history of each species were important factors in determining their longitudinal distribution.