Researchers from an international team, led by the Texas A&M College of Veterinary Medicine and Biomedical Sciences (VMBS), have identified extraordinary immune gene diversity in Atlantic herring.
The findings, published in Science Advances on Aug. 28, 2026, indicate that these fish possess a level of genetic variation in major histocompatibility complex (MHC) class II genes that exceeds that of any other vertebrate studied to date, including humans.
Atlantic herring form massive schools containing hundreds of millions or even billions of individuals. While this abundance makes them one of the most successful vertebrates on Earth, it also creates conditions conducive to the rapid spread of viruses, bacteria, and parasites.
The study suggests that the exceptional diversity in their immune genes reflects millions of years of natural selection as the species adapted to defend against a changing array of pathogens.
MHC molecules are critical to the vertebrate immune system because they help recognize harmful invaders by presenting fragments of foreign proteins to immune cells. Greater genetic diversity in these regions generally provides broader protection against disease. However, accurately measuring this diversity has historically been difficult due to the complex nature of MHC gene clusters.
To overcome this challenge, the research team sequenced the complete genomes of 14 fish collected from three geographic locations across the species’ range. They utilized long-read sequencing technology, which reads DNA in one continuous stretch rather than shorter fragments. This method allowed for high-quality genome assembly and unprecedented resolution of complex gene regions.
