Electrical Activity and Predation in the Clariid Catfish Clarias macrocephalus (Clariidae) Exposed to Varying Illumination

The influence of illumination (light–dark) on electrical emission in a clariid catfish Clarias macrocephalus hunting fast-moving prey (guppies Poecilia reticulata ) has been studied. A total of five types of electrical events has been registered, of which monopolar electrical pulses are classified as specialized electrical discharges. Pulses with multiple polarity reversal and long duration are myograms accompanying the locomotor activity of fish. Pulses with noticeable ruggedness, brief pulses, and a series of pulses can be considered intermediate between the two categories of electrical discharges. The emission of electrical discharges occurs mainly in the dark, which corresponds to the daily feeding chronology in clariid catfishes. It has been first shown that catfish can emit all types of electrical events, including specialized discharges, even when a single fish is isolated. The obtained results confirm that clariid catfish belongs to the weakly electric fishes with episodic emission of specialized electrical discharges. The evolutionary pathway of electric fishes from nonelectric ancestral forms with episodic unspecialized emission of nonsynchronized action potentials to forms that emit more and more synchronized action potentials and further to specialized electric fishes, including strongly electric ones and/or those using electrical discharges for location and communication, is discussed.