Cannibalism, Food Availability, and Reproduction in the Mosquito Fish (Gambusia affinis): A Laboratory Experiment

The relationship between food availability, cannibalism, and reproduction was investigated experimentally in the live-bearing fish Gambusia affinis. A two-way factorial design was used, with juvenile conspecifics (present or absent) and food (high, variable, or low) as the treatment variables. The results show a significant effect of food level on the occurrence of cannibalism. Cannibalism in turn has an interesting influence on reproductive output. Reproductive output is significantly different between groups in which the incidence of cannibalism is low (high-food treatment). Here, fish in the juveniles-present treatment have a much lower output than fish in the juveniles-absent treatment. The hypothesis that cannibalism allows the maintenance of a prior reproductive commitment when food availability declines is supported by trends in the data, but these patterns are not statistically significant. In Gambusia, cannibalism appears to provide the individual with a means of reducing the negative effects of competition for food on reproductive output. Hence, cannibalistic behavior may have important demographic consequences when it occurs in a natural population.