Intensive fish farming: changes in water quality and relationship with zooplankton community

Abstract Aim This study aimed to evaluate the interference of intensive fish farming in the physicochemical variables of water and in the zooplankton community from a tilapia (Oreochromis niloticus Linnaeus, 1758) pond in southern Brazil. In addition, it was verified whether the analyzed zooplankton groups could be bioindicators of changes in the quality of pond water. Methods The water and zooplankton sample collections were carried out monthly in different places of the pond: at the water supply site (affluent), in the middle of the pond and at the water outlet site (effluent). Analyzes related to nitrogen series (total nitrogen, total ammonia, nitrite + nitrate), dissolved oxygen, total hardness, total alkalinity, total phosphorus, pH, turbidity and water temperature were performed at all sampling sites. In addition, the density of the zooplankton groups Copepoda (adults and nauplii), Rotifera and Cladocera was determined. Results Regarding the changes between the quality variables of the affluent and effluent water of the pond, the outlet water showed a significant increase only in the variable total alkalinity. Rotifers were the most abundant organisms, and nauplii Copepoda showed a significant increase in the density of organisms in the middle of the pond compared to the inlet water. Both the redundancy analysis (RDA) and the Spearman correlation matrix revealed that zooplanktonic groups are associated with certain physicochemical variables of the water. According to the Analysis of Indicator Species (IndVal), the evaluated organisms are not related to bioindicator species in this environment. Conclusions Therefore, intensive production of O. niloticus caused changes only in the total alkalinity of the pond water. The zooplanktonic organisms correlated with the physicochemical variables of the water and between the groups, and did not show potential for bioindicators of water quality in the different locations of the pond.