International Journal of Aquaculture, 2025, Vol.15, No.2, 88-98 http://www.aquapublisher.com/index.php/ija 91 early stage: the Neotropical catfish suborders (Loricarioidei and Diplomystoidei) and the remaining Siluroidei suborder. In other words, the South American armored catfish suborder (Loricarioidei, including benthic adsorbed groups such as the family of Siluroidei) was restored as the most basal evolutionary branch in the order Siluriformes, followed by the Diplomystidae, which is also distributed in South America, together forming the basal group of the order Siluroidei. This result is consistent with the hypothesis that "Siluriformes originated in the Gondwana ancient land and spread outward from South America." On this basis, the vast majority of the remaining catfish families (collectively known as the Siluroidei) further differentiated into several large branches, among which the geographical distribution can be summarized as the two major evolutionary lines of "Asia + America branch" and "Africa branch" (Kappas et al., 2016; Brito et al., 2024). Long before the emergence of molecular evidence, studies based on fossils and limited molecular markers have proposed the concepts of "Big Asia" and "Big Africa". The latest mitochondrial genome phylogenetic tree well supports this view and makes a more detailed description of the family-level relationship. 4.2 Identification of deep divergence nodes and time estimation Specifically, in the “Asia+America clade”, several families living in East Asia and North America were found to be closely related, such as the Cranoglaniidae (only found in China) and the Ictaluridae (only found in North America) forming a sister group, which together with the marine Ariidae (mainly distributed in subtropical and tropical coastal waters) and Pangasiidae (Southeast Asia) form a highly supported monophyletic clade on the phylogenetic tree (Schedel et al., 2022). Interestingly, the African-specific Austroglanididae (endemic to South Africa) was not classified as a branch with other African catfishes in the molecular tree, but was clearly embedded in the above-mentioned Asian clade as a sister group of Pangasiidae (Duong et al., 2023). This discovery updates our understanding of the evolutionary status of African catfishes: the family Clariidae was traditionally believed to be a member of the African lineage, but new evidence shows that it shares a closer common ancestor with the Asian giant catfish family. In terms of the "African lineage", it mainly includes several families such as the Mochokidae (commonly known as the upside-down catfish) and the Claroteidae, which live on the African continent. They form a monophyletic group with each other and are sister groups to the above-mentioned "Asian + American lineage". 4.3 Comparison of new lineages with existing taxonomy In addition to the lineage division at the continental scale, mitochondrial genome data also clarified many systematic relationships between and within families. For example, molecular phylogenetic trees consistently support that the Clariidae (mainly distributed in Africa and South Asia) and the Heteropneustidae (South Asia) are the closest relatives to each other. Both families have auxiliary respiratory organs in anatomy, and molecular evidence confirms the kinship behind their convergent characteristics. For example, the American families Doradidae and Auchenipteridae are both thoracic catfishes, and their taxonomic status has long been unclear. The latest phylogenetic analysis shows that the two families constitute sister groups and evolved together in the freshwater system of South America. In terms of the relationship within the family, the affiliation of some genera that were controversial in the past has also been resolved with molecular evidence. For example, the classification of the subfamily Pelteobagrus in East Asia (formerly classified into the genus Pseudobagrus and the genus Leiocassis, etc.) has been confusing for a long time. Through mitochondrial genome analysis, it was found that these species with different genus names are actually clustered into one branch and have no obvious difference from the genus Tachysurus (whip catfish) (Zou et al., 2020). This result is consistent with the new classification scheme based on morphology, that is, Leiocassis, Pseudobagrus, Pelteobagrus, etc. are incorporated into the genus Tachysurus and unified into the broad genus Pelteobagrus. For example, the famous Bagridae family in the Siluriformes was found not to be a strictly monophyletic group in the past: the South Asian genus Rita is independent of other cichlids on the molecular phylogenetic tree. The latest study has also verified this again. Rita rita is not clustered on the main trunk of the cichlid family, but is closer to other groups, so that if it is excluded, the rest of the cichlid family can form a monophyletic group. It is suggested that the taxonomic status of the genus Rita should be re-evaluated, for example, it may be necessary to set up a separate family for it (Zhang et al., 2022).
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