Meet the fish with 30× more DNA than humans

A new genomic heavyweight has been crowned in the animal kingdom: the South American lungfish (Lepidosiren paradoxa) now holds the record for the largest sequenced animal genome. Its DNA spans about 91 billion base pairs—roughly 30 times more than the human genome—yet it encodes a comparable number of genes, around 20,000. The vast majority of this genetic material is noncoding, dominated by repetitive transposable elements, or “selfish” DNA that copies and pastes itself throughout the genome. Comparative analyses with other lungfish species indicate that L. paradoxa has effectively been adding the equivalent of an entire human genome’s worth of DNA every 10 million years. Because lungfish are considered “living fossils” and close relatives of the ancestors of all land vertebrates, decoding their genomes offers a rare window into vertebrate evolutionary history.

Researchers found that South American and African lungfishes lack key genes that normally suppress the spread of these transposable elements, allowing their genomes to expand with little restraint. This genomic bloat comes at a potential biological cost: all but one of the fish’s 19 chromosomes are each about the size of the entire human genome, demanding substantial energy to replicate and enlarge the nuclei and cells that house them. While such large genomes can occasionally foster adaptation—by tweaking gene activity or providing raw material for new genes—runaway expansion can also threaten organismal viability if gene regulation becomes unmanageable. Although some plants, such as New Caledonia’s fork fern and the Japanese shrub Paris japonica, have even larger genomes, L. paradoxa appears to be the current front-runner among animals, though unsequenced contenders like the marbled lungfish may yet challenge its title.

References (APA style)

Pennisi, E. (2024, August 14). This odd fish has 30 times as much DNA as humans—a new record for animals. Science.  

Meyer, A., Schartl, M., & colleagues. (2024). The genome of the South American lungfish Lepidosiren paradoxa and the evolution of vertebrate genome size. Nature.