Sound production in the reproductive behaviour of the weakly electric fish, Pollimyrus marianne Kramer et al. 2003 (Mormyridae, Teleostei)

In addition to their electric organ discharges, two West African mormyrid species are known to generate sounds during reproduction. Here, we document the reproductive behaviour and concurrent vocalisations recorded in captive specimens of the new species Pollimyrus marianne from the Upper Zambezi River. Prior to spawning, three male P. marianne established a territory and built a nest of filamentous plant material each (that would hold eggs and larvae at a later stage). Beginning with territory establishment and usually at night, only the males generated two distinct vocalisations, a tonal moan (average duration, 2.26 ± SD 0.6 s), and a harsh grunt (0.596 ± SD 0.029 s; grunt pulse repetition rate, PRR, 32.1 ± SD 1.24 Hz at 25.4 ± SD 0.15 °C). Both vocalisation types were similar to, but clearly different from, those recorded in the two West African species, P. isidori and P. adspersus, the PRR (Pulse Repetition Rate) of which were higher by 25% and 60%, respectively (at similar temperature). At constant standard length, some of a male P. marianne’s sound characteristics varied only slightly over two years, but depended clearly on water temperature. When no other fish were present, the three males produced moans only sporadically. When, however, females were visiting, the males generated long-lasting moan sequences that were superimposed by grunts (moan-grunt bouts; average duration, 14.69 ± SD 2.2 s). The maximum rate of vocalisation occurred in the nights immediately before spawning; this rate receded when larvae were present in the nest, and vocalisations finally stopped after the larvae had dispersed. Vocalisation rate increased again when females restarted to visit the nest site. Long before and also after reproduction, territorial males vocalised with moans and some grunts, when territory intruders evoked escalating agonistic interactions that were correlated with many bites or butts. In agonistic contexts, moan duration, moan peak amplitude frequency and grunt pulse repetition rate differed from the sounds produced during courtship. In P. marianne, the generation of sounds during reproductive and agonistic interactions suggests a dual function: attraction of mates and threatening competing males, or potentially egg-eating females.