The African weakly electric elephantfish family Mormyridae comprises 22 genera and almost 230 species. Up-to-date cytogenetic information was available for 17 species representing 14 genera. Here we report chromosome number and morphology in Hyperopisus bebe (Lacepède, 1803) and Pollimyrus isidori (Valenciennes, 1847) collected from the White Nile system in southwestern Ethiopia. Both taxa displayed the diploid chromosome number 2n = 40, but they differed in fundamental numbers: FN = 66 in H. bebe and FN = 72 in P. isidori; previously the same diploid chromosome number 2n = 40 was reported in an undescribed species of Pollimyrus Taverne, 1971 (FN = 42) from the same region. Our results demonstrate that not only pericentric inversions, but fusions also played a substantial role in the evolution of the mormyrid karyotype structure. If the hypothesis that the karyotype structure with 2n = 50–52 and prevalence of the uni-armed chromosomes close to the ancestral condition for the family Mormyridae is correct, the most derived karyotype structures are found in the Mormyrus Linnaeus, 1758 species with 2n = 50 and the highest number of bi-armed elements in their compliments compared to all other mormyrids and in Pollimyrus isidori with the highest number of bi-armed elements among the mormyrids with 2n = 40.

中文翻译：

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两个象鱼属（Hyperopisus 和Pollimyrus）的衍生核型：Mormyridae（Osteoglossiformes）中最低的染色体数

非洲弱电象鱼科 Mormyridae 包括 22 属和近 230 种。可获得代表 14 个属的 17 个物种的最新细胞遗传学信息。在这里，我们报告了从埃塞俄比亚西南部的白尼罗河系统收集的 Hyperopisus bebe (Lacepède, 1803) 和 Pollimyrus isidori (Valenciennes, 1847) 的染色体数量和形态。两个分类群都显示出二倍体染色体数 2n = 40，但它们的基本数目不同：H.​​ bebe 的 FN = 66 和 P. isidori 的 FN = 72；以前在同一地区的 Pollimyrus Taverne，1971 种（FN = 42）中报道了相同的二倍体染色体数 2n = 40。我们的结果表明，不仅是中心倒位，而且融合也在 mormyrid 核型结构的演变中发挥了重要作用。