ANALYSIS OF ELECTRIC DISCHARGES AND PREY CAPTURE BEHAVIOUR IN ELECTRIC CATFISH MALAPTERURUS ELECTRICUS GMELIN 1789 (SILUROIDEA MALAPTERURIDAE LACEP 1803)

1. 55 electric catfishes (4.5-60 cm long) have been studied. - The electric catfish, Malapterurus electricus, produces monophasic pulses of only one type. The duration of a single pulse is a function of water temperature (1.3 msec at 28° C) (Fig. 3). 19 electric catfishes, used in these experiments, discharged impulses from 25 to 182 V (measurements were made in water of a specific resistance of 1700 Ohm · cm). 2. The electric discharge of Malapterurus consists of bursts, which are composed of several pulses (Fig. 6). These bursts are elicited not only when the fish is touched, but also and very regularly during the capture of its prey, a little fish. Wheras the bursts, released by tapping the head or body of the fish consist of 3-67 pulses (most frequently 10-12 pulses) (Fig. 5), the number of pulses per burst fluctuates between 14 and 562 while swallowing its prey. 3. The pulse rate within a burst varies over a large range and only the beginning of a burst is marked by a low fluctuation of signal frequency. In this part of discharge the pulse rate is at its highest and correlated to the temperature of the aquarian water (450 Hz at 28° C) (Fig. 12). From the initial maximum to the end of the burst the repetition rate decreases, but another stimulation of the fish again rises the frequency. 4. The electric discharges of the catfish are part of the prey capturing behaviour. Immediately while thrusting forward and snapping at its prey, the catfish emits the first signals (Figs. 14and 15). The discharge is correlated to the subsequential reactions and stops after the prey is swallowed. When Malapterurus catches a small prey its bursts are short (35-1524 ms), but when the prey is large they become longer (max. 24,8 sec). 5. The most important stimulus, which releases the prey capturing behaviour together with electric discharges is a gustatory one. A Malapterurus, touched at the tail with a glass-rod, covered with mucus of other fishes, at once emits a long train of pulses. If all sensory pathways, going from the tail to the brain, are eliminated, except Ramus lateralis accessorius VII, which innervates the terminal buds at the trunk and tail, the animal shows still the described reactions. But when the R. lat. acc. VII is cut, no more discharges could be observed. 6. Snapping reaction and discharges are also elicited by small water disturbances produced in the vicinity of the head of the catfish. 7. Fishes whose vision and sense of smell have been eliminated show no failure in prey capture. 8. Some blinded individuals were trained to weak artificial electric stimuli. Conditioning is easily and quickly established. The catfish is very sensitive to such stimuli. © 1968 Springer-Verlag.