Impact of electric field exposure and salinity on behaviour of common carp (Cyprinus carpio) during entanglement of fishing gear

Electric fishing is one of the research methods used for sampling of aquatic species in freshwater and riverine habitats. Also in the marine environment using electric fields to reduce by-catch species and increase targeted fishing activities specially is a common useful method on particular for benthoses species. Electric current density and environmental factors such as water salinity can have different effects on fish species. Therefore, the study of behavioral changes and possible physical effects of electrical currents on fish species are important in terms of biological aspects and changes in population distribution for target prey species. The present study aimed to investigate changes in behavior of common carp (Cyprinus carpio) in experimental pond condition using a variable voltage electric field in different water salinity during entanglement of fishing gear. Common carp behavioral reactions in response to the strength and conductivity of the electric field in the water with different salinity and temperature such as distance from the source of electric current, fear reactions, convulsions and ultimately death of the fish when they were in the test environment were measured. In this study electric field treatments include a range of voltages 240, 225, 210, 195, 180, 165, 150,135, 120, 105 and 90 V in four water salinity levels (0, 2, 4 and 8 g/l) , respectively. The results showed that an increasing of water salinity (0-8) g /l does not have a significant effect on the distance of carp from the electric source. While, the increase in voltage has significant impact on the distance of carp from the electric source. Also in all water salinity treatments the maximum convulsion has been recorded in voltages higher than 150 volts. Mortality was observed at higher voltages above 225 v. Further complementary behavioural studies are needed to investigate potential effects of anthropogenic environmental pollutions including electric fields, produced by commercial fish pond mechanization and fisheries gear developments on fish species behavioural changes in both growing ponds and commercial fisheries activities. Moreover, we suggest that to understand the effects of environmental pollutions at the community levels require more laboratory and field experiments on many fish species at individual levels.