Keywords
Osteoglossiformes
Bony tongues
Non-monophyletic
Cytogenetics
Clade
Bony tongues
Non-monophyletic
Cytogenetics
Clade
Abstract
Pollimyrus is a non-monophyletic and paraphyletic species-rich Mormyridae genus that is still cytogenetically understudied. Here, the chromosome composition of Pollimyrus adspersus in the Oluwa River, Nigeria, was investigated for the first time to determine its karyotype and highlight the cytogenetic relationship between it and the two earlier studied species in the genus. Mitotic cells were arrested at the metaphase stage after a 0.05% peritoneal colchicine injection at 0.05ml per 10g of fish weight for 1 hour. Metaphase chromosomes were extracted from the fish kidney following the standard procedure. Slide staining was done using 6% Giemsa solution. Chromosome metaphases were snapped and processed in Photoshop. Chromosomes were characterised as metacentric, submetacentric, and acrocentric based on centromeric position. Chromosome homologs were paired and arranged in descending order of size. The chromosome number of 2n = 50 all acrocentric; 2n = 50 (50a), recovered from the fish, represents one of the least rearranged Mormyridae chromosome conditions, and was significantly different from its Ethiopian cogenerics; P. nigricans and P. isidori. The present study provides cytogenetic Evidence supporting an earlier morphologically based study that separated the studied species and its Ethiopian counterparts into different clades. Given previous cytogenetic and morphological data and the result presented herein, the appropriateness of retaining the species in the Pollimyrus genus should be reviewed. However, further studies incorporating molecular genetics, electrical organ discharge, and cytogenetics are essential for a more robust approach to the genus taxonomy.
References
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Bertollo, L. A. C., Cioffi, M. B. and Moreira-Filho, O. (2015). Direct Chromosome Preparation from Freshwater Teleost Fishes. In: Ozouf-Costaz, C., Pisano, E., Foresti, F., Almeida Toledo, L. F. (eds). Fish Cytogenetic Techniques (Chondrichthyans and Teleosts) (Vol. CRC Press: Enfield, USA. 1:21-26.
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Canitz, J., Kirschbaun, F. and Tiedermann, R. (2017). Karyotype Description of the African Weakly Electric Fish, Campylomormyrus compressirostris, in the Context of Chromosome Evolution in Osteoglossiformes. Journal of Physiology Paris, 110 (3), 273 – 280. https://doi:10.1016/j.physparis.2017.01.002.
Cioffi, M. B., Moreira-Filho, O., Ráb, P. Sember, A., Molina, W. F. & Bertollo, L. A. C. (2018). Conventional Cytogenetic Approaches—Useful and Indispensable Tools in Discovering Fish Biodiversity. Current Genetic Medicine Reports, 6:176 186. https://doi.org/10.1007/s40142-018-0148-7.
Cioffi, M. B., Ráb, P., Ezaz, T., Bertollo, L. A. C., L., S. Oliveira, E. A., Sember, A., Molina, W. F., Souza, F. H. S., Majtánová, Z., Liehr, T., Al-Rikabi, A. B. H., Yano, C. F., Viana, P., Feldberg, E., Unmack, P., Hatanaka, T., Tanomtong, A., & Perez, M. F. (2019). Deciphering the Evolutionary History of Arowana Fishes (Teleostei, Osteoglossiformes, Osteoglossidae): Insight from Comparative Cytogenomics. International Journal of Molecular Science, 20, Article 4296. https://doi.org/10.3390/ijms20174296.
de Souza, F. H. S., Sassi, F. M. C., Ferreira, P. H. N., Bertollo, L. A. C., Ezaz, T., Liehr, T., Perez, M. F. & Cioffi, M. B. (2022). Integrating Cytogenetics and Population Genomics: Allopatry and Neo-Sex Chromosomes May Have Shaped the Genetic Divergence in the Erythrinus erythrinus Species Complex (Teleostei, Characiformes). Biology, 11:315. https://doi.org/10.3390/biology11020315.
Dierickx, K., Wamuini Lunkayilakio, S., Bills, R., & Vreven, E. (2025). Morphometric Synthesis of Pollimyrus (Teleostei, Mormyridae) with the Description of Four New Species. Journal of Fish Biology, 106(3), 846–892. https://doi.org/10.1111/jfb.15983.
Fricke, R., Eschmeyer, W. N. & Van der Laan, R. (eds) (2025). Eschmeyer's Catalogue of Fishes: Genera, Species, References. (http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp).
Froese, R. & Pauly, D. (2025). FishBase. World Wide Web Electronic Publication. [Online] Available www.fishbase.org.
Hatanaka, T., Oliveira, E. A., Rab, P., Yano, C. F., Bertollo, L. A. C., Ezaz, T., Jegede, O. I., Liehr, T., Olaleye, V. F. & Cioffi, M. B. (2018). First Chromosomal Analysis in Gymnarchus niloticus (Gymnarchidae, Osteoglossiformes): Insights into the Karyotype Evolution of this Ancient Fish Order. Biological Journal of the Linnean Society, 20(1), 1–10. https://doi.org/10.1093/biolinnean/blx051.
Helfman, G. S., Collette, R. B., Facey, D. E., & Bowen, R. B. (2009). The Diversity of Fishes: Biology, Evolution and Ecology. Wiley–Blackwell, a John Wiley and Sons, Ltd. Publication, p.738.
Hilton, E. J. & Lavoue, S. (2018). A Review of the Systematic Biology of Fossil and Living Bony-Tongue Fishes, Osteoglossomorpha (Actinopterygii: Teleostei). Neotropical Ichthyology, 16(3), 1–35. https://doi.org/10.1093/biolinnean/bly098.
Jegede, O. I., Akintoye, M. A., & Awopetu, J. I. (2018). Karyotype of the African Weakly Electric Fish, Gymnarchus niloticus (Osteoglosiformes: Gymnarchidae) from Oluwa River, Nigeria. Ife Journal of Science, 20(3), 539–545.
Jegede O. I. (2022a). Karyotype of a Nigerian Population of Hyperopisus bebe (Osteoglossiformes: Mormyridae) Revealed Another Evolutionary Lineage in the Monospecific Genus: Hyperopisus. Ife Journal of Science, 24(2), 361–370. https://dx.doi.org/10.4314/ijs.v24i2.15.
Jegede, O. I. (2022b). Chromosomal Analysis of the Freshwater Fish Mormyrus rume (Mormyridae) from Asejire Reservoir, Oyo State, Nigeria. Nigerian Journal of Fisheries, 19(1), 2452 – 2458.
Jegede, O. I. (2022c). Karyotype of a Population of the Elephantnose Fish, Gnathonemus petersii (Osteoglossiformes: Mormyridae) from Oluwa River, Ondo State, Nigeria. Nigerian Journal of Tropical Agriculture, 26:22-30.
Kramer, B., van der Bank, F. H., & Wink, M. (2013). Marked Differentiation in a New Species of Dwarf Stonebasher, Pollimyrus cuandoensis sp. nov. (Mormyridae: Teleostei), from a Contact Zone with two Sibling Species of the Okavango and Zambezi Rivers. Journal of Natural History, 48(7–8), 429–463. https://doi.org/10.1080/00222933.2013.807950.
Kramer, B. & Wink, M. (2013). East-West Differentiation in the Marcusenius macrolepidotus Species Complex in Southern Africa: The Description of a New Species from the Lower Cunene River, Namibia (Teleostei: Mormyridae), Journal of Natural History, 47(35–36), 2327–2362. http://dx.doi.org/10.1080/00222933.2013.798699.
Kretschmer, R.; Franz, I.; de Souza, M. S.; Garnero, A. D. V.; Gunski, R. J.; de Oliveira, E. H. C.; O’Connor, R. E.; Griffin, D. K. & de Freitas, T. R. O. (2021). Cytogenetic Evidence Clarifies the Phylogeny of the Family Rhynchocyclidae (Aves: Passeriformes), Cells, 10:2650. https://doi.org/10.3390/cells10102650.
Krysanov, E. Y. & Golubtsov, A. S. (2014). Karyotypes of Four Fish Species from the Nile and Omo-Turkana Basins in Ethiopia. Journal of Ichthyology, 54(10), 889–892.
Lavoué, S., Bigorne, R., Lecointre, G. and Agnèse, J., (2000). Phylogenetic Relationships of Mormyrid Electric Fishes (Mormyridae; Teleostei) Inferred from Cytochrome b Sequences, Molecular Phylogenetics and Evolution, 14(1), 1-10. https://doi.org/10.1006/mpev.1999.0687.
Lavoue, S., Sullivan, J. P., & Arnegard, M. E. (2010). African Weakly Electric Fishes of the Genus Petrocephalus (Osteoglossomorpha: Mormyridae) of Odzala National Park, Republic of the Congo (Lékoli River, Congo River Basin) with Description of Five New Species. Zootaxa, 2600, 1–52. https://doi.org/10.11646/zootaxa.2600.1.1.
Levan, A., Fredgaa, K. & Sandberg, A. A. (1964). Nomenclature for Centromeric Position on Chromosomes. Hereditas, 52:201-220. https://doi.org/10.1111/j.1601-5223.1964.tb01953.x.
Levin, B. A. & Golubtsov, A. S. (2018). New Insights into the Molecular Phylogeny and Taxonomy of Mormyrids (Osteoglossiformes, Actinopterygii) In Northern East Africa. Journal of Zoological Systematics and Evolutionary Research, 56(1), 61–76. https://doi.org/10.1111/jzs.12186.
Maake, P. A., Gon, O. & Swartz, E. R. (2014). Description of Three New Species of Marcusenius Gill, 1862 (Teleostei: Mormyridae) from South Africa and Mozambique. Zootaxa, 370(3), 455-480.
Ozouf-Costaz, C., Coutanceau, J., Bonillo, C., Belkadi, L., Fermon, Y., Agnese. J., Guidi-Rontani, C. and Paugy, D. (2015). First Insights into Karyotype Evolution Within the Family Mormyridae. Cybium, 39(3),227-236. https://doi.org/10.26028/cybium/2015-393-006.
Paula, G. B. N., Gavazzoni, M., Zawadzki, C. H., Fernandes, C. A., Portela-Castro, A. L. B., Lui, R. L. & Margarido, V. P. (2022). Identification of Cryptic Species in Allopatric Populations of Hypostomus tietensis (Siluriformes: Loricariidae) Through Cytogenetics Analyses. Neotropical Ichthyology, 20(2), Article e210158. https://doi.org/10.1590/1982-0224-2021-0158.
Peterson, R. D., Sullivan, J. P., Hopkins, C. D., Santaquiteria, A., Dillman, C. B., Pirro, S., Betancur-R, R., Arcila, D., Hughes, L. C., & Ortí, G. (2022). Phylogenomics of Bony-Tongue Fishes (Osteoglossomorpha) Shed Light on the Craniofacial Evolution and Biogeography of the Weakly Electric Clade (Mormyridae). Systematic Biology, 71(5),1032–1044. https://doi.org/10.1093/sysbio/syac001.
Rich, M., Sullivan, J. P., & Hopkins, C. D. (2017). Rediscovery and Description of Paramormyrops sphekodes (Sauvage, 1879) and a New Cryptic Paramormyrops (Mormyridae: Osteoglossiformes) from the Ogooué River of Gabon Using Morphometrics, DNA Sequencing, and Electrophysiology. Zoological Journal of the Linnean Society, 180:613–646. https://doi.org/10.1093/zoolinnean/zlw004.
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