Age and growth patterns of the ten spotted live-bearing fish (Cnesterodon decemmaculatus) along a polluted freshwater system.

Age and growth patterns of fish provide important information about the effects of environmental disturbances, which can be used as comparative tools in subsequent studies that attempt to assess freshwater quality. The main goal of our study was to provide information on relevant biological aspects of a native fish species used as a bioindicator in an extensive area of South America. In particular, we evaluated the age and growth patterns of Cnesterodon decemmaculatus (Poeciliidae) to establish reference species values and to compare them in different sites along an environmental quality gradient in a South American freshwater system. Water quality assessments indicated increasing environmental degradation downstream, reflecting anthropogenic impacts. The estimated ages of C. decemmaculatus along this quality gradient varied across sampling sites. The longest-lived individuals were those from the reference site, also presenting the highest average age value (almost 2 years). The best model to describe the growth in length of the individuals was the Logistic model. According to the parameters estimated from the growth curves, individuals from the most disturbed site showed slower growth although they reached greater maximum lengths than fish from the other sites. These results suggest that fish would tolerate the adverse conditions of the most altered sites, allocating their energy differentially. Our study provides valuable information on the age and growth patterns of C. decemmaculatus, a species endemic to the Neotropical region and a useful bioindicator in ecotoxicological studies.