Migration of two atyid shrimps, Caridina sakishimensis (Fujino and Shokita, 1976) and Caridina typus (H. Millne Edwards, 1937) in Urabaru, Kikai-jima Island, Southern Japan

Abstract

The present study was conducted to study the presence of amphidromy in two atyid shrimps Caridina sakishimensis and Caridina typus along the continuum of Urabaru stream. Study was carried out to clearly outline the life cycle of an endangered atyid C. sakishimensis and its co-existing species C. typus. Entire continuum of stream was divided into five stations (St.1, St. 2, St. 3, St. 4 and St. 5). Monthly sampling was carried out using a scoop net (1 × 1 mm) via the sweep method, sweeping efforts were counted. The results revealed that C. sakishiemnsis was restricted at St. 1 only, a few juveniles of C. sakishiemnsis were recorded at St. 3, St. 4. The length frequency histograms showed the occurrence of large number of juveniles at St. 3, 4 and 5 in smaller length groups. Also C. typus ovigerous females exhibiting spawning migration to the downstream and its juvenile also migrate back to upstream after completing the larval development in Urbaru stream were also observed. Presence of C. sakishsimensis at only St. 1 indicates the species is not using the river continuum for migration. Due to cave dwelling habit of C. sakishsimensis and coral origin of Kikai-jima Island it can be concluded that the species might be using the underground river system for migration.