International Journal of Aquaculture, 2025, Vol.15, No.5, 255-265 http://www.aquapublisher.com/index.php/ija 255 Research Report Open Access Evolutionary Pathways of Fishes: Insights from Fossil Records and Molecular Phylogenetics Xianming Li 1, Lingfei Jin 2 1 Aquatic Biology Research Center, Cuixi Academy of Biotechnology, Zhuji, 311800, Zhejiang, China 2 Institute of Life Science, Jiyang College of Zhejiang A&F University, Zhuji, 311800, Zhejiang, China Corresponding author: lingfei.jin@jicat.org International Journal of Aquaculture, 2025, Vol.15, No.5 doi: 10.5376/ija.2025.15.0025 Received: 20 Aug., 2025 Accepted: 10 Oct., 2025 Published: 25 Oct., 2025 Copyright © 2025 Li and Jin, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Li X.M., and Jin L.F., 2025, Evolutionary pathways of fishes: insights from fossil records and molecular phylogenetics, International Journal of Aquaculture, 15(5): 255-265 (doi: 10.5376/ija.2025.15.0025) Abstract Fish, as the oldest and diverse group of vertebrates, play an important role in the history of biological evolution. This study summarizes the main stages and characteristics of fish evolution pathways, focusing on combining fossil record with molecular phylogenetic research to reveal the evolution of fish from early jawless fish to modern diversified taxa. We reviewed the important discoveries of early jawless fish fossils and the outbreak of fish diversity during the Silurian and Devonian periods; explored the profound impact of the origin of the jaw on predation strategies, as well as the early differentiation of boneless and cartilage fish in the Paleozoic era. Analysis of morphological characteristics and molecular phylogenetic evidence of radial fin fish. Based on the latest molecular phylogenetic research, we reconstructed the evolutionary relationships of important fish populations and conducted case analysis in combination with key evolutionary events. Finally, we emphasize the importance of combining fossil evidence with molecular clock calibration, and combining fossil and molecular insights can help deepen our understanding of the origins and adaptive evolution mechanisms of fish biodiversity. Keywords Fish evolution; Fossil record; Molecular phylogenetic; Origin of jaw; Adaptive radiation 1 Introduction Fish are the earliest vertebrates and the most abundant vertebrate group. In the history of animal evolution, the emergence of fish marks an important stage in the evolution of vertebrates, and its evolutionary path is of foundational significance for understanding the subsequent emergence of amphibians, reptiles, birds and mammals. As early as the late Cambrian period, the earliest vertebrates similar to fish had appeared in the ocean, such as the Haikou fish and Kunming fish found in Chengjiang, China, and are considered to be the oldest known vertebrate fossils (Cartwright and Collins, 2007). After Ordovician-Silurian radiation, fish gradually differentiated into multiple branches, including jawless and jawless, laying the foundation for the further evolution of vertebrates. Fossil record provides direct morphological evidence and chronological frameworks that allow us to reconstruct key nodes in fish evolution. Fossils can determine when a certain group first appeared, what anatomical characteristics it had, and how these characteristics change over time. But fossil evidence alone is often not sufficient to fully reveal the evolutionary relationship: fossil records have problems with incomplete and biasedness, and some soft body features are difficult to preserve (Carroll, 2012). At the same time, the fossil abundance of strata in different periods varies due to geological processes. Therefore, the introduction of molecular phylogenetic methods can compensate for the shortcomings of fossil record by comparing the genome and molecular characteristics of fresh fish (Chen et al., 2014). This study will sort out the important fossil discoveries about the early evolution of fish in the field of paleontology, including the emergence, diversity and extinction events of jawless and jawless fish; summarize the new understanding of the relationship between major fish taxa by molecular phylogenetics, such as redefining the internal phylogenetic structure of bone fish through high-throughput sequencing data; analyze several key evolutionary events and adaptive radiation cases, explore the integration of fossils and molecular evidence, and
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