The weatherfish is a living barometer that breathes through its own digestive tract

Nature · Published 3 October 2026 Swipe more like this →

In short: Known as the European weatherfish, this slender loach is far more than a bottom-dwelling scavenger. It possesses the uncanny ability to sense shifts in barometric pressure, reacting with frantic activity when the weather turns. Even more remarkable is its biological hack for surviving in oxygen-depleted waters: it breathes through its intestines.

The weatherfish, or Misgurnus fossilis, is a true loach found across a vast European and Asian range, stretching from the Meuse River in the west to the Volga and Ural drainages in the east. These fish are long and thin, an evolutionary adaptation that allows them to burrow into the substrate and navigate dense aquatic vegetation where other species struggle. While typically reaching lengths of 30 cm, some anecdotal reports from fishermen suggest they may grow as large as 45 cm, potentially making them the largest of all true loach species.

The species earns its common name from its sensitivity to atmospheric pressure. When barometric conditions shift, the fish becomes visibly agitated, swimming excitedly near the surface. This behavior is linked to its unique survival mechanism: when oxygen levels in the water drop, the weatherfish rises to the surface to gulp air. This air travels through the digestive system, where a complex network of blood vessels in the intestinal mucous membrane extracts oxygen before the gas is expelled through the anus.

Despite being classified as a species of least concern, the weatherfish faces significant threats from human activity. Because both adults and juveniles rely heavily on dense vegetation or detritus-rich shorelines, practices like dredging and the removal of aquatic weeds can devastate local populations. Consequently, while not currently endangered, the weatherfish is legally protected across most of its natural range to ensure its survival in the varied, often challenging habitats it calls home.

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