Migratory History of the Fourspine Sculpin Rheopresbe kazika, a National Monument Species in Japan

Abstract

The fourspine sculpin Rheopresbe kazika is a cottid fish endemic to Japan, and this fish is designated as a national monument species in some areas of the country. The natural population of the fish has decreased in recent years, and therefore various efforts have been made to establish an efficient culture system for this species. However, there is little information available regarding the life history and migration of the species. The migratory history of R. kazika was examined in terms of strontium (Sr) and calcium (Ca) uptake in the otolith by means of wavelength dispersive X-ray spectrometry on an electron microprobe. The Sr:Ca ratios in the otoliths changed with the salinity of the habitat. The otoliths of R. kazika fluctuated strongly along the life history transects in accordance to their migration patterns from seawater to freshwater. The Sr:Ca ratios within R.kazika averaged 4.15 × 10− 3 in the otolith region from the core to the point (360–475 µm) and decreased to lower levels which averaged 1.37 × 10− 3, in the outer otolith region. The data suggest that this species has a catadromous life cycle and the otolith Sr:Ca ratios reflect individual life histories within R. kazika.