Laboratory experiments examined now aggressive behavior, use of space, activity and breathing frequency were affected by the number of fish competing for a concentrated, renewing, intermittent food source. Total aggression rate per fish and the proportion of long chases decreased in larger groups and increased during short periods in which food was unavailable. The proportional use of the area near the food source was maximal at intermediate group sizes suggesting that use of the feeding area was reduced by aggressive defense at low densities and by passive interference at high densities. Air-breathing frequency tended to be lower when food was available than when it was not, suggesting that gouramis reduce their use of atmospheric oxygen when it may result in loss of food to competitors. Group size affects the pattern of food competition more through economic resource defense than through passive interference.

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