Predation by Crangonid Shrimp on Juvenile Japanese Flounder under Laboratory Conditions

Abstract

The predator-prey relationship of crangonid shrimp Crangon affinis and juvenile Japanese flounder Paralichthys olivaceus was examined under laboratory conditions. Visual observation and the carcasses of the juvenile flounder provided an insight to the pred-atory process. The shrimp hooked the juvenile flounder with their movable chela, and devoured in the order of the abdomen, tail, trunk, eyes, and head. Predation rates: the percentage of flounder lethally attacked by the shrimp per container and numbers of lethally attacked flounder juveniles per shrimp decreased as the size of the flounder increased. These values were greater during dark periods than during light periods. This fact indicates that shrimp are more active and effective predators at night. The daily ration of shrimp was roughly estimated to be 20–25 % of their body weight, based on the mean weight of prey con-sumed daily per I g of the predator. The maximum size of flounder susceptible to shrimp predation was expected to be larger than 25 mm SL. These results suggest that predation pressured by shrimp is considerably heavy on newly-settled Japanese flounder, especially at night. © 1993, The Japanese Society of Fisheries Science. All rights reserved.