Physiological responses of nile tilapia and water parameters after decomposition of macrophyte using herbicide

Abstract

Macrophytes are important for aquatic biocenosis, however under certain conditions its population can raise becoming a problem in reservoirs, such as the Egeria densa. To control these plants, CONAMA discuss for the use of chemicals, but feasibility and safety studies should be conducted to allow the use for such purpose. Thus, the present study evaluated the effects of decomposition of Egeria densa killed by the herbicide diquat on water quality variables and physiological responses of Nile tilapia. Thus, 176 tilapias were distributed in 16 tanks and submitted to four treatments (tilapia without macrophyte; tilapia and macrophyte; tilapia and macrophyte died by diquat; and macrophyte died by freezing). The values of pH, temperature, dissolved oxygen, alkalinity and conductivity did not differ between treatments. However, an increase in total ammonia and phosphorus and reduction of nitrite concentrations in treatment with macrophyte killed by the herbicide was observed. Chlorophyll-a concentration did not differ between treatments, however, phaeophytin-a increased in water submitted to plants died by freezing. After 21 days of experiment, no differences were observed in blood glucose, cortisol, leukocytes, erythrocytes and hemoglobin. Thus, tilapia does not alter their physiological patterns after chronic exposure to decomposing macrophytes killed by diquat.