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 predatory process. The shrimp hooked the juvenile flounder with their movable chcla, 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 consumed daily per 1g of the predator. The maximum size of flounder susceptible to shrimp predation was expected to be larger than 25mm SL. These results suggest that predation pressured by shrimp is considerably heavy on newly-settled Japanese flounder, especially at night.