Utilização de microsternarchus bilineatus (ostariophysi, gymnotiformes, hypopomidae) como biomonitor: o efeito de combustíveis automotivos derivados do petróleo na descarga do órgão elétrico

Abstract

This study evaluated the effect of automotive fuel (gasoline and diesel) on the Electric Organ Discharge (EOD) frequency of Microsternarchus bilineatus (Ostariophysi, Gymnotiform), with the objective of testing the viability of this species as a biomonitor to detect pollutant derived from petroleum. Ten individuals of the species were exposed to concentrations of 110 μL/L and 220μL/L for each of the pollutant tested. Those concentrations correspond, respectively, to 25% and 50% of the Tolerance Limit (LTm) for fish in continental waters. Each experiment lasted for 9 hours, as the first hour was used to acclimate the individuals in the experimental tanks. From the second hour on, the EODs recordings started with 2 minutes duration, in 15 minutes intervals. From the second until fifth hour was considered as a pre-contamination period, and the EODs of this phase were compared with the recordings made after the addition of the pollutant. After the release of the pollutant in the tank, the recordings continued for an additional four hours (pos-contamination period). The bioelectrical signal was captured through a pair of electrodes placed in the tanks, amplified, and then visualized in real time with a digital oscilloscope. The signal was recorded with the aid of an analog to digital converter (16 bits resolution) and analyzed with the program MATLAB. Statistical analyzes were performed on the discharge frequencies pre and pos-contamination. Once the heterogeneity of the data was detected, the paired student t-test (p<0.05) was applied comparing values pre and pos-contamination. Both gasoline and diesel, in the concentrations tested, provoked changes in the DOEs frequencies of Microsternarchus. Nine out of the ten individual tested changed the discharge rhythm for gasoline 110 μL/L, and seven for the concentration of 220 μL/L. For diesel at 110 μL/L, nine out of ten individuals changed their frequency and, for 220 μL/L, nine out of ten individuals tested altered their discharge pattern. From the 34 individuals that had their DOEs altered, 85,30% changed their frequencies within the first hour of exposition to the contaminants. Variations in the results can be occurring due to the individual tolerance to the contaminants, however, the results obtained until now, suggest that Microsternarchus has a great potential to be utilized as a biomonitor species in aquatic environments. The present study also opens a wide number of possibilities for future studies, where the investigations started here could be complemented by the utilization of different concentrations, different pollutants, and other parameters associated to DOEs to be analyzed, besides the frequencies.