Factors associated with parasite aggregation levels in fishes from Brazil.

The degree of parasite aggregation is determined by a number of factors that are not well understood. In total, 3,746 fish from 73 species and their parasites were analyzed to determine associations between the degree of aggregation by taxon and specific characteristics of the fish. A multiple linear regression (95% confidence interval - CI) was used to show that in most taxa, the degree of parasite aggregation was significantly higher in freshwater fish and schooling fish but varied according to taxon in relation to gender, habitat and feeding habits. Parasite aggregations were also significantly increased in fish with a large number of parasitic larvae and greater body length in all evaluated taxa. Because the coefficients of determination of the models were lower than 60% for all taxa, other factors may be involved in parasite aggregation. Conversely, marked significance was observed for the tested variables in relation to taxon dependence, which indicates that additional studies should be performed for these factors using comprehensive databases with larger samples per parasite species.