Laboratory Studies of Predation by the Hyperiid Amphipiod Parathemisto japonica on Larvae of the Japanese Sand-eel Ammodytes personatus

Abstract

The ability of the hyperiid amphipod Parathemisto japonica to feed on larvae of the Japanese sand-eel Ammodytes personatus were studied in the laboratory. The number of larvae eaten by P. japonica increased with increase in predator size, up to 27.4 of 1-3-day-old larvae were consumed per 12 h under light conditions. The feeding rate became higher as the number of larvae offered was increased, showing a functional response that approached a maximum rate asymptotically. P. japonica consumed 13-15-day-old larvae (6.0-6.3mm in notochord length) to the same degree as 1-3-day-old larvae (4.7-5.1 mm in notochord length) in terms of wet weight. The feeding activity of P. japonica was higher during daytime than at night. Larger P. japonica (3.8-4.5mm in head plus thorax length) consumed from 13.1 to 36.7 1-3-day-old larvae per day and the daily ration ranged from 38.1% to 59.9%. These feeding experiments together with a field survey, suggest that predation of P. japonica has considerable effect on the survival of larval sand-eels in Otsuchi Bay and adjacent waters.