Efeito de combustíveis derivados do petróleo na descarga do órgão elétrico de Parapterontus Hasemani (ELLIS 1913) (Ostariophysi, Gymnotiformes)

Abstract

This study determined the circadian rhythm during for 24 hours period and the effect of automotive fuels (gasoline and diesel) on the discharge rate, coefficient of variation, amplitude and waveform shape oscillations of the Electric Organ Discharge (EOD) in the weakly electric fish Parapteronotus hasemani (Ostariophysis, Gymnotiformes), with the objective of testing the viability of this species as biomonitor to detect contaminants derived from petroleum. The individuals were exposed to concentrations of 110, 220 and 440 μl/5L and those concentrations corresponded to 25, 50 and 100% of concentration allowed for fish in continental waters. Each experiment lasted for 9 hours, as the 1st two hours were used to acclimate the individuals in the experimental tanks, pre- contamination started at the 3rd time, and EODs of this phase were compared with the recordings made after the addition of the contaminant, which followed by 4 more hours and from the 5th until 9th hour was considered as a pos-contamination period. The bioelectric signal was captured through a pair of electrodes placed in the experimental tanks, amplified, monitored, and visualized in real time a digital oscilloscope. The signal was recorded with an analog/digital converter (16-bit resolution) and analyzed with the program MATLAB ® , Mathworks. EODs recordings were 2 minutes duration, in 15 minutes intervals. Statistical analyzes of the circadian rhythm was detected through the paired Student’s t-Test (p≤0.05) was applied comparing the normalized values of the night and day period. Oscillations from gasoline and diesel experiments were detected through the analysis of repeated measures (ANOVA RM) followed by Bonferroni or Fisher's LSD post-hoc tests. The circadian rhythm had differences between the day-night oscillations in the discharge rate (p= 0.000), 1st area (p= 0.017), 3rd area (p= 0.000) and the ratio of the 1st area to 3rd area (p= 0.05) of the waveform shape. The variation was higher during the day, due higher values of standard deviations, determining regularity and stability of these parameters at night because they are synchronized to the feeding activity. The diesel oil caused an increase in discharge rate (p= 0.000) in 440 μl/5L, oscillation of the waveform shape in the 3rd area (p= 0.049) and the ratio of the 1st area to 3rd area (p= 0.045) and decreased the discharge rate in the concentration 110 μl/5L. The gasoline caused no significant oscillations waveform shape in the 1st area by Bonferroni post-hoc test. Variations have occurred due to the individual tolerance to the contaminants in the central nervous system in pacemaker nucleus. It is suggest P. hasemani has a great potential to be utilized as a biomonitor species in aquatic environments, because the effect of diesel determined by the minimum detectable species concentrations in a maximum time of 3 hours within 4 hours of exposure. This research presented new possibilities for future studies, where the investigations started here could be complemented by the utilization of higher concentrations, especially for exposure to gasoline.