Sexual and Aggressive Behavior, Density and Social Structure in A Natural Population of Mosquitofish, Gambusia affinis holbrooki

Abstract

quently included the category chase, a behavioral unit almost never seen in laboratory aquaria. The films also provided three examples of copulation, in which female tilting was observed. Aggression, infrequent and mild in the field, was frequent and more intense in the laboratory. Seasonal changes in population structure and behavior were analyzed; for example, winter grouping behavior dissolved at springtime; sexual activity peaked during the spring. A sex ratio of 1 9:5 $ 8 was apparently optimal for sexual activity. Two distinct population systems operated in the field. Mosquitofish were either over open water or concealed in vegetation along the shorelines of the study area. Since filming was possible only in the open water area, the population system concealed in vegetation was not adequately analyzed. Thus the comparison of density-dependent social behavior in the laboratory and field was valid only from the viewpoint of the open water system as representative of the field.