Occurrence and Hypoxic Tolerance of the Juvenile Metapenaeus ensis at the Mouth of the Yodo River, Osaka

Abstract

Temperature, salinity, oxygen saturation, and occurrence of the greasyback shrimp Metapenaeus ensis were measured at the mouth of the Yodo River in September 1992 and 1993. Indoor experiments were also conducted on the juvenile greasyback shrimp, juvenile kuruma prawn Penaeus (Mar-supenaeus) japonicus, young swimming crab Portunus (Portunus) trituberculatus, and the common brackish goby Acanthogobius flavimanus to examine their tolerance to low saturations of oxygen. The juvenile greasyback shrimp's habitat is at the bottom of the estuary where oxygen saturations decreased to 12-55%. Indoor experiments revealed that the mortality rate of the juvenile greasyback shrimp was only 25% when exposed to an oxygen saturation of 7-12% at 25°C for 24 h and that this shrimp has a high tolerance to hypoxic conditions compared with the other three species. These findings suggest that, in spite of low oxygen saturations, the mouth of the Yodo River still plays an important role as a growing ground for the greasyback shrimp depending on the tolerance to hypoxic conditions. © 1995, The Japanese Society of Fisheries Science. All rights reserved.