DIEL VARIATIONS IN GUT FULLNESS OF JUVENILE SPOT, LEIOSTOMUS-XANTHURUS (PISCES)

Juvenile spot, Leiostomus xanthurus (Pisces), were collected at 2-h intervals over two 48-h periods in a tidal creek in North Inlet, South Carolina, during July 1986. Gut fullness, dry gut contents weight as a percentage of fish wet weight, was measured to test the hypothesis that feeding intensity is randomly distributed through time. Spot were also collected and serially sacrificed from a holding tank to estimate their gut evacuation rate. Gut fullness was greatest during periods of ebb and high tides and was little affected by the amount of light available. Gut contents were evacuated at a rate of about 15% per hour in the laboratory, in close agreement with field emptying times of about 6 h from peak fullness to empty guts. A conservative estimate of daily ration for juvenile spot (19-42 mm standard length) was 4.5% of their live body weight per day. Studies of spot feeding ecology can be greatly affected by when fish are collected during the tidal cycle.