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A recent collection of African electric fish of the genus Petrocephalus from the Bangweulu-Mweru ecoregion of the Congo basin comprises two endemic species, Petrocephalus squalostoma (Boulenger, 1915), which was previously known only from its type specimens and another specimen, and a new species described herein as Petrocephalus frieli sp. nov. An exclusive set of morphological characters distinguishes P. frieli sp. nov. from P. squalostoma and all other species of Petrocephalus from the Congo basin. Petrocephalus frieli sp. nov. can further be distinguished from the East African Petrocephalus catostoma catostoma (Gunther, 1866) in having only 12 circumpenduncular scales (versus 15/16 in P. c. catostoma). A molecular phylogenetic analysis confirms the distinctiveness of P. squalostoma and P. frieli sp. nov. among a sampling of 18 species of Petrocephalus. Previous reports of Petrocephalus simus Sauvage, 1879 from the Bangweulu-Mweru ecoregion probably represent misidentifications and the occurrence of P....

This is the first description of vocalisations produced by the mormyrid species Petrocephalus catostoma from the Upper Zambezi River whilst defending a territory. Agonistic behavioural displays of a dominant male towards a conspecific, such as mutual circling or short attacks, were accompanied by characteristic tonal sounds, termed hoots. The mean hoot duration (43 ± SD 1.8 ms) was longer, and the fundamental frequency (Hi, 180 ± SD 4.7 Hz) lower, than in the closely related species Petrocephalus ballayi. P. catostoma vocalised hoots only during intraspecific agonistic interactions, especially those accompanying territorial conflict.

The mormyrids are well known for their remarkable electrogenic and electrolocation capabilities and exceptionally large cerebellum that may account for much of their total oxygen consumption. Mormyrids living in oxygen-deficient waters may use oxygen efficiently, protecting the brain from hypoxia damage; and/or brain size may be reduced. This study compares the TFL, gill lamellar density, gill lamellar area, total gill surface area, and brain size of two species of mormyrids from extremely hypoxic waters in Uganda (Gnathonemus victoriae and Petrocephalus catostoma) to two open-water species (Mormyrus kannume and Gnathonemus longibarbis) from the same region. In addition, interdemic variation was considered by comparing swamp populations of G. victoriae and P. catostoma to open-water populations of the same species. Total gill surface area of all species fell within the upper range for freshwater fishes. However, there were both intraspecific and interspecific differences in gill characters. Interdemic comparisons showed larger gill size in swamp-dwelling populations. Brain size varied among species; larger brains were characteristic of species from well-oxygenated waters. Large gill surface area may permit survival of mormyrids in oxygen-stressed environments; however, mechanisms compensating for hypoxia seem to be inadequate to support a brain size as large as that seen in fish from well-oxygenated waters.

The morphology of the sagittal otoliths of two South African mormyrid fish, Marcusenius macrolepidotus and Petrocephalus catostoma, were studied to determine possible morphological significance. The sagittae of M. macrolepidotus and P. catostoma are kidney-shaped and oblong, respectively. The ventral margin is slightly indented in the former and slightly flattened in the latter. The sulcus acusticus of both species is archaesulcoid but mesial in M. macrolepidotus and ostio-caudal in P. catostoma. The crista inferior in M. macrolepidotus is ridge-like and well defined posteriorly and anteriorly, whereas in P. catostoma it is clearly defined posteriorly and disappears anteriorly. The otoliths of both species do not have a rostrum, antirostrum or an excisura. The differences in sagittal morphology between the two mormyrid species are distinct.

East African and south African churchills (Petrocephalus, Mormyridae) were synonymised in 1959 to become members of a single species of subcontinental, southern African distribution, Petrocephalus catostoma (Gunther, 1866). By comparison with the type material for P. catostoma from the Ruvuma River and P. stuhlmanni from the Ruvu River, both of East African origin, we confirm the South African form of churchill to represent a new species, P. wesselsi, ranging from the northern Limpopo and Incomati systems south to the Pongola River (Natal) as its southern limit. We also compared churchills from the Sabie River (25° S, South Africa, Incomati system) with churchills from the Upper Zambezi River (17° S, Namibia), using electric organ discharges (EODs) and morphology. The duration of an EOD pulse of the South African form (N = 39; 943.2±S.E. 18.82 µs) is, on average, more than twice that of the Upper Zambezi form (N = 37; 436.6±15.1 µs), and the amplitude of the second head-positive phase (P2 phase relative to P1 = 1) significantly weaker (0.133 ± 0.0005 vs. 0.472 ± 0.002 for Upper Zambezi males, 0.363 ± 0.03 for Upper Zambezi females). In contrast to the Upper Zambezi form, the EOD of the South African form exhibits no difference between the sexes. Fish from the two origins differ significantly in 11 out of 14 anatomical characters studied, confirming molecular genetic differentiation on the species level.

changes in fish faunal structure and diversity. Though catches of many species had declined by the 1960s due to overexploitation (Kudhongania et al., 1992), the dramatic increase in Nile perch in the 1980s in Lake Victoria was followed by a drastic decline in the populations of several indigenous species (Kaufman, 1992). Most notable has been the disappearance of over 50% of the endemic haplochromine cichlids from Lake Victoria (Kaufman, 1992; Kaufman et al., 1997). However, many indigenous noncichlids, some of which were important in the pre-Nile perch fishery, have also declined or disappeared (Kaufman, 1992; Kudhongania et al., 1992). Similar trends have been observed in other