Bioacoustics of Synodontis

The genus Synodontis Cuvier, 1816 is the most species rich and widespread genus of mochokid catfishes. As currently recognized the genus contains approximately 120 valid species distributed throughout most of the freshwaters of sub-Saharan Africa and the Nile River system. Larger Synodontis species are important food fishes in many parts of Africa and are commonly known as “squeakers” because they readily produce sounds by stridulating their pectoral spines when handled or disturbed. Furthermore many Synodontis species are prized ornamental fishes because they have striking pigmentation patterns or display unusual behaviors like an upside down swimming posture. Poll (1971) last revised the entire genus and noted seven species reported from Gabon based on specimens he examined or previous published accounts and faunal lists: S. angelicus Schilthuis 1891 , S. albolineatus Pellegrin 1924 , S. guttatus Guenther 1865 , S. haugi Pellegrin 1906 , S. obesus Boulenger 1898 , S. polyodon Vaillant 1895 and S. tessmanni Pappenheim 1911 . Four of these species have well documented type localities within Gabon ( S. albolineatus , S. haugi , S. polyodon and S. tessmanni ) and appear to be endemics of the Ogooue or Ntem Rivers and their tributaries. In contrast, the presences of S. angelicus , S. guttatus , and S. obesus in Gabon are uncertain or possibly erroneous. First, the claim for S. angelicus is based on the junior synonym S. tholloni Boulenger 1901 known from a single specimen (MNHN 1890-0030) collected at an unspecified locality possibly within the Ogooue basin of Gabon. Otherwise, S. angelicus is known exclusively from the Congo basin. Second, Poll (1971) did not find any specimens of S. guttatus from Gabon, questioned published records from Gabon by Sauvage (1880, 1884) and concluded that the species is only found in the lower Niger basin. Finally, Boulenger (1898) described S. obesus based on three syntypes, one from the Opobo River, Nigeria (BMNH 1896.5.5.67) and two from an unspecified locality in Gabon (BMNH 1881.7.20.5-6). Poll (1971) subsequently designated the Nigerian syntype as the lectotype for S. obesus . Given this type fixation and the uncertain locality data for the paralectotypes, the presence of S. obesus in Gabon remains ambiguous. Since Poll’s revision, the first author and others have made many more collections of Gabonese fishes. Review of this material for an upcoming edited book on the freshwater fishes of West Central Africa (Lower Guinea) has revealed the presence of at least eight Synodontis species in Gabon. These include the previously known endemics ( S. albolineatus , S. haugi , S. polyodon , and S. tessmanni ), plus four additional species. One of these, S. batesii Boulenger 1907 , originally described from the Congo basin of Cameroon, is now known from both the Ogooue and Ntem basins of Gabon. The other newly recorded species are currently under study by several researchers. One of these new species that has unique bony ornamentation and sexual dimorphism is described here.