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We have investigated the detailed behavioral responses of Oreochromis niloticus exposed to direct current (DC) and 3 low frequencies of pulsed DC (PDC) (1 Hz, 3 Hz, 6 Hz). The study was aimed to find out the threshold current densities (µA/mm²) for the perception of electric field, galvanotaxis (involuntary movement towards the electrode) and narcosis (loss of equilibrium, unconsciousness). Effects on opercular movements before and after electrical exposure was extensively studied. The threshold values for all three responses were found to be higher in DC in comparison with PDC. Among three types of PDC (1, 3 and 6 Hz) applied in the experiments, the threshold values for all the three reactions (perception, taxis and narcosis) were lowest in PDC 6 Hz and highest in PDC 1 Hz followed by continuous DC and PDC 3 Hz. Anodal galvanotaxis was most effectively shown in 90% test individuals in both DC sharp rise and PDC 3 Hz. However, PDC 3 Hz is preferred over DC due to low current requirement. In case of DC, opercular movements were regained immediately after the removal of current, whereas fishes regained opercular movements within 20seconds- 1 minute after exposure in PDC. Though recovery after exposure was delayed upto 1 minute in PDC, it can be ignored as there was no mortality in the present study. So PDC 3 Hz may be a more sustainable option over DC sharp rise due to lower power consumption.
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