Alarm substances for the protection of ichthyofauna in the hydroelectric sector
fish confinement; alarm substances; hypoxanthine-3-N-oxide; chondroitin; repulsion.
Hydroelectric power plants normally interrupt power generation to carry out some maneuvers, test and mechanical maintenance on the generating units, which can cause the accumulation of fish biomass in the suction tube. Consequently, water quality determinants such as obtained oxygen, temperature and ammonia can be altered due to the long period of preparation for rescue activities of confined fish. Thus, the development of sustainable technologies that minimize fish trapping in hydroelectric plants is necessary. Alarm substances have the ability to change the behavior of fish exposed to it, causing alarm and repulsion reactions. These substances are naturally released after injury to the skin of fish as a sign of a defensive response to a danger situation. According to the literature, hypoxanthine-3-N-oxide and chondroitin are active compounds present in alarm substances and are synthesized and marketed. Considering the potential of these substances as a tool to protect the ichthyofauna, this study presents an investigation of the efficiency and feasibility of application in hydroelectric plants. The methodologies for applying the skin extract, hypoxanthine-3-N-oxide and chondroitin were developed in the laboratory and the evaluation of the behavior of the fish conditioned to these substances occurred remotely with the aid of instrumentalized treatments. Metabolism stress analyzes were also done through fish blood glucose determinations. The application at the Jirau Hydroelectric Plant, in Rondônia, occurred with the adaptation of the aeration system present in the generating units and the monitoring of the fish in the draft tube was done with the aid of a hydroacoustic monitoring system in real time. Matrinxã (Brycon cephalus) and Tambaqui (Colossoma macropomum) species exhibit anti-predatory reactions when exposed to hypoxanthine-3-N-oxide (3.0 and 6.0 µg L-1), chondroitin sulfate (5 µg L-1) and skin extracts of Matrinxã and Pirarucu species (Arapaima gigas). The most recurrent behaviors were fast swimming and organization, as well as lethargy and some episodes of aggression among the specimens. In the field, skin extracts and chondroitin sulfate caused some degree of disturbance, indicating the potential of these substances as a future method of protecting ichthyofauna in the hydroelectric sector.