On the reaction of marine fishes in interrupted A.C. of 50 Hz

The reactions of marine fishes in interrupted A. C. off uniform electrical field and constant current density have been studied in order to determine the optimum effective periods of shock: for narcosis and fixation. Higher effective periods were required with gradual decrease in potential difference between head and tail, which in turn depended on the length of fish and its position in electrical field. The body voltage of fish varied directly with the length and inversely with the rise of angle between their body axis and field lines. The fish subjected to higher effective period took longer time for recovery from narcosis. The effect of impulse current was manifested by increased rate of gill movements in Platax tefora, Haetodon ollaris, Crysophus burda, Siganus vermiculatus and Scolopsis leucotaenia, and lowered rate of movements in others when subjected to different effective periods inspective of length.

Response of fishes to the underwater D.C. field

Response to external electric field (D. C.) of three different varieties of fish namely Puntius ticto, Heteropneustis fossilis and Tilapia mossambica having different anatomical and behavioural characteristics were studied. Clearly distinguished reactions occurred one after another m all the varieties of fish with the increase in field intensity with minor specific variations. These reactions can be broadly classified into initial start (first reaction), forced swimming (galvanotaxis), slackening of body muscle (galvanonarcosis) and state of muscular rigidity (tetanus). The orientation of the organism (projection of nervous element) to the surrounding field has been found to have important bearing on the behaviour reactions. Clearly differentiated anodic taxis and true narcosis set in when fish body axis was parallel to the lines of current conduction. But with greater angle between the body axis and the current lines, fish did not show well marked reactions. Fish body, when perpendicular to current lines responded for anodic curvature and off balance swimming followed by tetanus.