Freshwater Fish Diversity and Phylogenetic Evolution

Freshwater fishes represent one of the most species-rich assemblages of vertebrates, with lineages distributed across rivers, lakes and wetlands on every continent except Antarctica. Molecular phylogenies have revealed that many modern clades arose through repeated habitat transitions, most notably multiple independent colonisations of freshwaters by ancestrally marine groups. These shifts have been driven by euryhaline tolerance and have often precipitated adaptive radiations, leading to remarkable morphological and ecological diversification in regions such as the African Great Lakes, Neotropical river basins and Southeast Asian floodplains. Phylogenomic approaches using whole-genome and mitochondrial data have clarified deep branching patterns, dated key divergence events and identified genomic signatures of selection associated with osmoregulatory, dietary and locomotor adaptations. Comparative analyses show that ecological factors—such as lake versus river habitats, species richness and clade age—play a crucial role in determining rates of phenotypic evolution. Understanding these patterns is critical for conservation, as habitat fragmentation, pollution and climate change threaten the evolutionary potential of many freshwater lineages.

Research from Nature Portfolio

Recent studies have employed long-read and whole-genome sequencing across multiple species of sea catfishes to reconstruct their evolutionary history over approximately 50 million years. Younger freshwater lineages exhibit elevated incidences of positive selection compared with their marine relatives, particularly in genes linked to body size and shape. A pronounced signature of selection on the prolactin gene family underscores the importance of osmoregulatory adaptation during transitions from marine to freshwater environments. This work demonstrates how genome-wide analyses can uncover the molecular basis of habitat-driven morphological innovation and yield a nuanced picture of adaptive radiation in a widely distributed teleost clade.

Freshwater Fish Diversity and Phylogenetic Evolution publication trend

The graph below shows the total number of articles in freshwater fish diversity and phylogenetic evolution across all publications each year (not limited to Nature Index journals).

Technical terms

Adaptive radiation: Rapid diversification of a lineage into a variety of ecological roles following colonisation of new habitats.

Mitogenomic phylogeny: Evolutionary tree constructed using complete mitochondrial genome sequences to infer species relationships and divergence times.

Osmoregulatory adaptation: Physiological modifications that enable organisms to maintain internal ion and water balance when moving between environments of differing salinity.

Euryhaline: Describing organisms capable of tolerating a wide range of salinities, facilitating transitions between marine and freshwater habitats.

References

1. Ecological diversification of sea catfishes is accompanied by genome-wide signatures of positive selection. Nature Communications (2024).
2. Salinity plays a limited role in determining rates of size evolution in fishes globally across multiple scales. Global Ecology and Biogeography (2024).
3. Multiple Invasions into Freshwater by Pufferfishes (Teleostei: Tetraodontidae): A Mitogenomic Perspective. PLOS ONE (2011).
4. Mitogenomic Evidence for an Indo-West Pacific Origin of the Clupeoidei (Teleostei: Clupeiformes). PLOS ONE (2013).