Ability of Creeping into Sand by Hatchery-reared ‘Hirame’ Paralichthys olivaceus

Abstract

Recently, hatchery-reared ‘hirame’ Paralichthys olivaceus, have been released at many places in this country. But these ‘hirame’ juvenile have not necessarily been released at the right place. The sand quality was one of the important conditions required of a place at which ‘hirame’ are released. Therefore the ability of creeping in sand of ‘hirame’ juvenile P. olivaceus, was examined. The ‘hirame’ juvenile examined may be categorised into four groups according to length, averaging total length of 23.0mm, 54.3mm, 75.4mm and 99.6mm. The sand of the sea bed was divided into seven sections according to grain size. Sand from each section was laid on the bottom of a 10L plastic container. Five to twenty fish were transferred to each container. The creeping ratio was measured visually at two and four hours after beginning of examination.
As the ‘hirame’ grew, their ability of creeping in sand increased. The 23.0mm TL ‘hirame’ was able to creep in the sand that was smaller than 0.5mm in grain size, but not in the sand that was larger than 0.5mm in grain size. The ‘hirame’ groups measuring more than 54.3mm TL were able to creep in the sand smaller than 1.0mm in grain size, but not in the sand that was larger than 1.0mm in grain size.