@article {667, title = {Organization of the stalk system on electrocytes in mormyrid weakly electric fish Campylomormyrus compressirostris}, journal = {Cell and Tissue Research}, year = {2024}, month = {Dec-20-2024}, pages = {1-17}, abstract = {

The adult electric organ in weakly electric mormyrid fish consists of action-potential-generating electrocytes, structurally and functionally modified skeletal muscle cells. The electrocytes have a disc-shaped portion and, on one of its sides, numerous thin processes, termed stalklets. These unite to stalks leading to a single main stalk that carries the innervation site. Here, we describe the 3-dimensional layout of the stalklet/stalk system in adult Campylomormyrus compressirostris by differential interference contrast microscopy and confocal fluorescence microscopy. Using antibodies against Na+/K+-ATPase \α-subunit and plasma membrane Ca2+-ATPase, we show that these ion pumps are differentially distributed over the stalklet/stalk system, with plasma membrane Ca2+-ATPase being enriched on the stalklet membrane. Stalklets are distributed and organized in a quite uniform pattern on the posterior face of the electrocyte disc and fuse to terminal stalks. The latter then unite in a mostly dichotomic mode to stalks of increasing thickness, with the main stalk measuring about 100\ \µm in diameter. We further analyse the structural organization of stalklets and stalks, with a characteristic cytoskeletal system of bundled actin filaments in the centre and nuclei in subsurface position. These results suggest that the stalklet/stalk system is adapted in its structural layout to generate an action potential highly synchronized over the entire disc-portion of the electrocyte, accounting for the short electric organ discharge in this species. Our results suggest that actin-related proteins overexpressed in electrocytes, as shown previously by transcriptome analysis, may be involved in the organization of the unique F-actin system in stalklets and stalks.

}, keywords = {Ca2+-ATPase, Confocal microscopy, electrocyte, F-actin, Plasma membrane, Sodium pump}, issn = {0302-766X, 1432-0878}, doi = {10.1007/s00441-024-03938-y}, url = {https://doi.org/10.1007/s00441-024-03938-y}, author = {Baumann, Otto and Cheng, Feng and Kirschbaum, Frank and Tiedemann, Ralph} } @article {664, title = {Biogeographic barriers are differentially permeable based on traits: Movement of hypoxia tolerant mormyrid fish in the Lake Victoria basin}, year = {2024}, month = {Nov-01-2024}, pages = {102485}, abstract = {

Lake Nabugabo is a small satellite lake separated from Lake Victoria by hypoxic swamps that impose a biogeographic barrier to fish assemblages. Some species occur exclusively in Nabugabo while others show high differentiation across this barrier, yet air-breathing fishes show nearly zero genetic differentiation between the two lakes. We hypothesize that hypoxia-tolerant fishes, unlike other non-air-breathing species, would have similarly low genetic differentiation across the barrier. We used pooled RAD-seq to examine the degree of genetic differentiation in two species of non-air-breathing but hypoxia-tolerant mormyrid fishes, Marcusenius victoriae and Petrocephalus degeni. Other non-air-breathing fishes have been shown to have FST values as low as 0.05 but mostly between 0.10 and 0.20; however, we discovered that the genetic differentiation in our focal species was very low, with FST values between 0.02 and 0.04, making them much more comparable to air-breathing fishes with FST values of near zero. We conclude that this and other analogous barriers should be understood as differentially permeable depending on the traits of the organisms crossing them, such as hypoxia tolerance in this case.

}, keywords = {Differentially permeable barriers, Hypoxia tolerance, Lake Nabugabo, Lake Victoria, Mormyridae, Population connectivity}, issn = {0380-1330}, doi = {10.1016/j.jglr.2024.102485}, url = {http://dx.doi.org/10.1016/j.jglr.2024.102485}, author = {Hunt, David A.G.A. and Thomas, Quinn and Clarke, Shelby B. and Chapman, Lauren J.} } @article {662, title = {Morphometric synthesis of Pollimyrus (Teleostei, Mormyridae) with the description of four new species}, journal = {Journal of Fish Biology}, volume = {2024}, year = {2024}, month = {Nov-24-2024}, pages = {1-47}, abstract = {

Mormyridae, a species-rich family endemic to Africa, remains taxonomically understudied. This has been the case for the genus Pollimyrus Taverne, 1971, which hinders further understanding of the distribution, ecology, and conservation of its species. Therefore, an in-depth morphometric comparison of all currently valid species is carried out using most of the available type specimens. Species delineations were re-evaluated, and four species new to science described: Pollimyrus ibalazambai sp. nov. (the Luki River, the Democratic Republic of the Congo), Pollimyrus krameri sp. nov. (the Lugenda River, Mozambique), Pollimyrus vanneeri sp. nov. (the Kouilou-Niari River, the Republic of the Congo), and Pollimyrus weyli sp. nov. (the Buzi River, Mozambique). In this study, Pollimyrus guttatus is confirmed to belong to Pollimyrus, whereas Pollimyrus eburneensis and Cyphomyrus plagiostoma seem more similar to species allocated to other genera. No or only little morphological differences were found between the type series of several species, which could indicate the need for synonymization of these species (Pollimyrus cuandoensis with Pollimyrus marianne and Pollimyrus nigripinnis with Pollimyrus pulverulentus). As such 20 species are currently morphologically identifiable in the genus Pollimyrus. The present study highlights the critical need for further synthetic efforts and new collecting efforts across Africa for this and other Mormyridae genera.

}, keywords = {morphology, Pollimyrus ibalazambai sp. nov., Pollimyrus krameri sp. nov., Pollimyrus vanneeri sp. nov., Pollimyrus weyli sp. nov., Taxonomy}, issn = {0022-1112, 1095-8649}, doi = {10.1111/jfb.15983}, url = {http://dx.doi.org/10.1111/jfb.15983}, author = {Dierickx, Katrien and Wamuini Lunkayilakio, Soleil and Bills, Roger and Vreven, Emmanuel} } @article {660, title = {Diet of some fish species of the family Mormyridae (Actinopterygii: Teleostei; Bonaparte, 1831) from the upper Sanaga River, Central Region of Cameroon}, journal = {Journal of Animal Diversity}, volume = {6}, year = {2024}, month = {31 March 2024}, pages = {51-62}, chapter = {51}, abstract = {

This study was carried out between October 2020 and October 2021 with the aim of determining sustainable management options and nutrition for the domestication of Mormyridae fish species living in the Sanaga River in central Cameroon. For this purpose, 451 specimens collected from local fishermen were identified and grouped into four genera and seven species, constituting 20.84\% Campylomormyrus phantasticus (Pellegrin), 5.32\% Hippopotamyrus castor (Pappenheim), 24.61\% Mormyrops anguilloides (Linnaeus), 18.63\% Mormyrops caballus (Pellegrin), 4.66\% Mormyrops zanclirostris (G\ünther, 1867), 15.52\% Mormyrus rume (Valenciennes), and 10.42\% Mormyrus tapirus (Pappenheim). Fish were measured, and parameters were obtained after dissection using intestinal morphometric characteristics and stomach content analysis methods. The emptiness coefficient varied from 0\% (Hippopotamyrus castor and Mormyrops zanclirostris) to 26.66\% (Mormyrus rume). The relative mass of the intestine was low in all studied species; the intestinal coefficient and the Zihler index of all these species are within the range of carnivorous species. Analysis of stomach contents revealed a broad food spectrum containing twelve categories of prey. Insects, macrophytes and larval insect shelters were the preferred foods of Mormyrops anguilloides, Mormyrops caballus and Mormyrops zanclirostris, while insect larvae and larval shelters were the preferred prey for other species. Site and season had little effect on the categories of prey consumed by these species.

}, keywords = {Biodiversity, Ebebda, feeding, Monatele, Mormyridae, stomach contents}, doi = {10.22034/JAD.2024.6.1.5}, url = {http://dx.doi.org/10.22034/JAD.2024.6.1.5}, author = {Akohogni, MAM and Medjo, KE and Zebaze, TB and Chiassa, NKA and Mepa, TCP and Tiogu{\'e}, TC and Fon, ED} } @article {647, title = {A review of the reproductive biology of mormyroid~fishes: An emerging model for biomedical research}, journal = {Journal of Experimental Zoology Part B: Molecular and Developmental EvolutionJournal of Experimental Zoology Part B: Molecular and Developmental EvolutionJ Exp Zool B Mol Dev Evol}, volume = {342}, year = {2024}, month = {2024/05/01}, pages = {144 - 163}, publisher = {John Wiley \& Sons, Ltd}, abstract = {Abstract Mormyroidea is a superfamily of weakly electric African fishes with great potential as a model in a variety of biomedical research areas including systems neuroscience, muscle cell and craniofacial development, ion channel biophysics, and flagellar/ciliary biology. However, they are currently difficult to breed in the laboratory setting, which is essential for any tractable model organism. As such, there is a need to better understand the reproductive biology of mormyroids to breed them more reliably in the laboratory to effectively use them as a biomedical research model. This review seeks to (1)~briefly highlight the biomedically relevant phenotypes of mormyroids and (2) compile information about mormyroid reproduction including sex differences, breeding season, sexual maturity, gonads, gametes, and courtship/spawning behaviors. We also highlight areas of mormyroid reproductive biology that are currently unexplored and/or have the potential for further investigation that may provide insights into more successful mormyroid laboratory breeding methods.}, keywords = {biomedicine, electric fish, mormyrid, reproduction, teleost}, isbn = {1552-5007}, url = {https://doi.org/10.1002/jez.b.23242}, author = {Saunders, Alyssa N. and Jason R. Gallant} } @article {644, title = {Trophic ecology of the African riverine elephant fishes (Mormyridae)}, volume = {14}, year = {2024}, month = {Aug-01-2024}, abstract = {

Multiple species of the elephant fishes (Mormyridae) commonly coexist in sympatry in most African tropical rivers and lakes. In this study, we investigated the trophic ecology and potential trophic niche partitioning of eleven mormyrid fish species from the Sanaga River system in Cameroon using the stable isotope composition of carbon and nitrogen in the muscle samples. Albeit most mormyrids mainly feed on invertebrates, we found differences in isotope ratios, and we report signs of the trophic niche partitioning among species. We further found significant differences in isotopic signatures within the Mormyrus genus, suggesting ecological niche diversification among three closely related species. We have also evaluated differences in the isotopic signals between seasons in four species, which could be possibly caused by species migration and/or anthropogenic agricultural activities. To evaluate body shape, we applied geometric morphometric analyses, and we show that most of the species are clearly morphologically separated. We focused on the mormyrid ecomorphology to identify a possible interaction between shape and ecology, and we found a relationship between the \δ13C (but not \δ15N) isotopic signal and morphology, suggesting their interplay during mormyrid evolution. Overall, we present robust evidence of the trophic niche partitioning within the mormyrid species community, and we integrate trophic ecology with morphometrics, shedding light on the enigmatic evolutionary history of these fascinating African fishes.

}, keywords = {mormyrids, stable isotopes, trophic ecology, trophic position, trophic resource portioning}, issn = {2045-7758, 2045-7758}, doi = {10.1002/ece3.70173}, url = {http://dx.doi.org/10.1002/ece3.70173}, author = {Sommer, Gina Maria and Njom, Samuel Didier and Indermaur, Adrian and Nyom, Arnold Roger Bitja and Jandov{\'a}, Kate{\v r}ina and Kukla, Jaroslav and Petrt{\'y}l, Miloslav and Hork{\'a}, Petra and Musilova, Zuzana} } @article {643, title = {Fossils indicate marine dispersal in osteoglossid fishes, a classic example of continental vicariance}, volume = {291}, year = {2024}, month = {Aug-01-2024}, abstract = {

The separation of closely related terrestrial or freshwater species by vast marine barriers represents a biogeographical riddle. Such cases can provide evidence for vicariance, a process whereby ancient geological events like continental rifting divided ancestral geographical ranges. With an evolutionary history extending tens of millions of years, freshwater ecology, and distribution encompassing widely separated southern landmasses, osteoglossid bonytongue fishes are a textbook case of vicariance attributed to Mesozoic fragmentation of the Gondwanan supercontinent. Largely overlooked fossils complicate the clean narrative invoked for extant species by recording occurrences on additional continents and in marine settings. Here, we present a new total-evidence phylogenetic hypothesis for bonytongue fishes combined with quantitative models of range evolution and show that the last common ancestor of extant osteoglossids was likely marine, and that the group colonized freshwater settings at least four times when both extant and extinct lineages are considered. The correspondence between extant osteoglossid relationships and patterns of continental fragmentation therefore represents a striking example of biogeographical pseudocongruence. Contrary to arguments against vicariance hypotheses that rely only on temporal or phylogenetic evidence, these results provide direct palaeontological support for enhanced dispersal ability early in the history of a group with widely separated distributions in the modern day.

}, issn = {0962-8452, 1471-2954}, doi = {10.1098/rspb.2024.1293}, url = {http://dx.doi.org/10.1098/rspb.2024.1293}, author = {Capobianco, Alessio and Friedman, Matt} } @article {642, title = {Overall diet of four species of Marcusenius (M. monteiri, M. stanleyanus, M. sp.{\textquoteright}malebo{\textquoteright} and M. schilthuisiae) from Pool Malebo, Congo River, Kinshasa}, journal = {African Journal of Biological Sciences}, volume = {6}, year = {2024}, month = {08/2024}, pages = {4195-4217}, chapter = {4195}, abstract = {

The objective of this study was to analyze and compare the diet of four Marcusenius species living in the Malebo Pool. The Intestinal Coefficient of these fish ranges from 0.55 to 0.67. These average values make it possible to classify these species in the trophic group of invertivores (larvae of aquatic insects). The analysis of variance at the 5\% threshold reveals that there is not a statistically significant difference between the average intestinal coefficients of 4 species of Marcusenius (Fischer = 2.46963; p = 0.06). stomach contents of M. monteiri, M. stanleyanus, M. schilthuisiae and M. sp.\&$\#$39;malebo\&$\#$39; confirm an invertivorous diet, with a predominance of benthic insect larvae, followed by crustaceans, periphyton and macrocosm organisms benthic that they find in their habitats.

}, keywords = {diet, index, intestinal coefficient, invertebrate, prey}, doi = {10.33472/AFJBS.6.5.2024.4195-4217}, url = {https://doi.org/10.33472/AFJBS.6.5.2024.4195-4217}, author = {Jean M{\'e}tis Ntu Mabedi and Victorine Mbadu Zebe and Jean-Claude, Micha and Michaux Johan, R.} } @article {640, title = {A new type of spermiogenesis in teleost fish: formation of the aflagellate sperm in Campylomormyrus compressirostris (Osteoglossomorpha: Mormyridae)}, journal = {Zoology}, year = {2024}, month = {29 June 2024}, abstract = {

Osteoglossomorpha, the bony tongue fishes, show great variation in morphology, behavioural strategies, reproductive biology and gamete ultrastructure. The order Osteoglossiformes is the only vertebrate taxon, in which four types of sperm (monoflagellate, biflagellate and aflagellate aquasperm and the complex introsperm) have been described. It is also the only vertebrate lineage in which aflagellate spermatozoa exist. The aim of this study was to analyse the structure of the testis and the process of spermiogenesis in the mormyrid Campylomormyrus compressirostris during the breeding season using light and electron microscopy (transmission and scanning). Males of this species have a single testis of the anastomosing tubular type. The tubules of the anterior part of the testis contain cysts with developing germ cells, and this region is much wider than the posterior part, which consists of efferent ducts filled with sperm cells. The cysts are filled with single or mitotic spermatogonia, primary and secondary spermatocytes and early spermatids. At the stage of spermatids with fine granular chromatin, the cysts rupture and successive stages of spermatid differentiation take place in the testicular lumen; we therefore characterise this process as \‘extracystic spermiogenesis\’. Sperm development in C. compressirostris is extremely simple and involves chromatin condensation in the central region of the nucleus, a slight decrease in nuclear volume, the appearance of numerous vesicles in the cytoplasm that form a tubular-vesicular system at the base of the nucleus. Both centrioles and mitochondria are translocated to the peripheral region of the midpiece, which forms the opposite pole to the nucleus. There are many differences between the types of spermiogenesis described so far in teleosts and that found in C. compressirostris, including the loss of flagellum formation. This unique type of spermiogenesis is restricted to species of the families Mormyridae and Gymnarchidae, all of which possess aflagellate spermatozoa. Our data demonstrate that the spermatid differentiation and existence of the aflagellate spermatozoon are a unique phenomena not only among teleosts but also in the whole vertebrate lineage.

}, keywords = {elephantfish, permatozoon, Sertoli cells, spermatids, Tubular testis}, doi = {10.1016/j.zool.2024.126186}, url = {https://www.sciencedirect.com/science/article/pii/S094420062400045X}, author = {Dymek, Anna M and Kirschbaum, Frank and Ralph Tiedemann and Siemi{\'n}ski, Krzysztof and Pecio, Anna} }