Supersaturação gasosa em tilápias-do-nilo (Oreochromis niloticus) em tanques-rede: um estudo de caso sobre os impactos da operação hidrelétrica no Rio Iguaçu

Abstract

The aquaculture sector, particularly the intensive farming of Nile tilapia (Oreochromis niloticus) in net-cage systems, shows continuous expansion, contributing significantly to economic progress and food security, with the state of Paraná being the national leader in this production. Given the dependence of intensive systems on water quality, this case study aimed to analyze the factors that culminated in a massive fish mortality event at a fish farm located in a hydroelectric power plant reservoir. The main event, which occurred in October 2023, resulted in the immediate loss of approximately 120,516 tilapias (about 52.8 tonnes of biomass), with the total volume of dead fish removed over the subsequent 10 days reaching about 400 tonnes. The methodology consisted of the analysis and discussion of retrospective data obtained from technical reports and media outlets. The results of the documentary research revealed that the event was preceded by intense rainfall and the unannounced opening of the dam gates. Clinical inspection of the dead fish evidenced gas embolism, with the presence of bubbles in the fins, and environmental monitoring registered an oxygen supersaturation of approximately 132% in the water, a level that exceeds safety limits and is directly associated with the observed pathology. The conclusion is that the mass mortality was caused by Gas Bubble Disease, a severe physiological disorder resulting from the acute dissolved gas imbalance, triggered by the combination of climatic conditions and the dam's hydraulic dynamics. The study proposes urgent preventive measures, such as the implementation of continuous monitoring of total dissolved gas pressure and the establishment of a rigorous hydrological communication and operation protocol between the plant and the fish farm, aiming to enhance the productive safety and environmental sustainability of the farming system.