On mating and function of associated electric pulses in Clarias macrocephalus (Günther 1864): probing an old puzzle, first posed by Charles Darwin

The Asian broadhead walking catfish ( Clarias macrocephalus ) generates weak electric monopolar pulses during spawning. Males emit a single pulse when attracting a female, and while in amplexus, only females emit a single burst of similar pulses. This burst is a necessary component in the mating ritual of C. macrocephalus . Release of milt occurs about 5 s prior to the onset of a burst, which is immediately followed by the release of eggs. Following sperm release, the male remains in tight embrace with the female. Though both male and female could perceive each other’s electric pulses via ampullary receptors (communication mode), we postulate that egg release can be facilitated by direct action of the female’s burst on the male’s neuromuscular system (contraction mode). Shedding light on the function of weak episodic electric emission, we propose that the modification of electrogenic structures evolved towards increasing the efficiency of direct bodily impact. As extant clariids exhibit intermediate features between non-electric and strongly electric catfishes, Clarias should be considered a “serviceable transition,” which Charles Darwin deemed a possible intermediate form between these two groups.