School and shoal distributions in a freshwater catfish species, Corydoras paleatus (Callichthyidae)

The South American armored catfish Corydoras paleatus has been observed to occur in nature in various aggregations, individually or in pairs. These catfishes are advantageous for laboratory study because their swimming, foraging, and resting behaviors are easily quantified and they school in two dimensions rather than three. In observational studies, we examined positioning of individuals within aggregations, number of groups typically present within an aggregation, how individuals proportion themselves and their time among aggregations and resting behaviors, and the density-dependence of these factors. We found that groups become more cohesive with increasing density and that preferred density is approxiamately 10 individuals. In choice experiments, we examined the effects of density, familiarity, satiation, and touch on shoal choice. Individuals always chose the larger density and chose familiar individuals for equal densities. Satiation primarily influenced the strength of choice. Touch had a small but nonsignificant affect on strengh of choice.