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Fish

Weatherfish

Misgurnus fossilis

Weatherfish

General Overview

Zvârluga is the largest European loach, a fascinating benthic fish of the Cobitidae family, known for its remarkable ability to survive in extreme environmental conditions - it tolerates very low concentrations of dissolved oxygen and high water temperatures. It is called "weatherfish" because it becomes extremely active before storms and barometric changes - behavior historically used for weather prediction. Serpentine body, elongated like a snake. It has 10 barbels (whiskers) around its mouth - more than any other European loach. It can air breathe - it swallows air at the surface and processes it in the intestine for oxygen extraction (intestinal respiration). It lives in marshes, swamps, silty canals and dense vegetation. Buried in the mud by day, active by night. Protected in many European countries but not in Romania - used as live nada.

Physical Characteristics

The body is extremely elongated, serpentine, and cylindrical, making the weatherfish Europe's largest loach with typical lengths of 20–30 cm and a maximum of 35 cm. The head is small, relatively flat, with tiny eyes — an adaptation to a subterranean life in sediment. The most important diagnostic feature is the 10 barbels (whiskers) around the mouth: 4 on the upper jaw, 2 at the corner of the mouth, and 4 on the lower jaw. Scales are small, embedded in the thick skin covered with a generous layer of slippery mucus that facilitates movement through sediment. The coloration is brownish-yellow to ochre, with dark longitudinal stripes on the flanks alternating with lighter areas, creating a striped pattern. The belly is lighter, yellow-orange in color. The tail is short and rounded. The musculature is strong, enabling rapid undulating movements through the substrate.

Habitat & Distribution

The weatherfish has a wide distribution across Central and Eastern Europe, extending eastward into Central Asia. In Romania it is found mainly in low-lying plains: marshes, ponds, eutrophic lakes with dense vegetation, irrigation canals, and oxbow lakes of lowland rivers. The Danube Delta represents an ideal habitat — ponds with deep mud and dense reed and cattail vegetation offer optimal conditions for this species. The weatherfish requires specific conditions: low dissolved oxygen (tolerable thanks to intestinal breathing), relatively high summer temperatures, abundant mud in which to burrow, and emergent or submerged vegetation. Preferred depths are shallow, under 1 metre, in peripheral zones of lakes and ponds. It is entirely absent from cold mountain waters or fast-flowing rivers.

Behavior & Feeding

The weatherfish is a benthic omnivore scavenger with a varied and opportunistic diet. It consumes copepods, cladocerans, ostracods, oligochaetes, chironomid larvae, aquatic beetle larvae, small gastropods, and large quantities of organic detritus. Unlike other cobitids, the weatherfish feeds both by day and night, though nocturnal activity predominates. Its unique capacity for intestinal breathing — swallowing air at the water surface and processing oxygen in the intestine — allows it to survive in hypoxic waters where other species would already be dead. The behavior of intense agitation before storms and atmospheric pressure changes is well documented and was used for centuries as an informal weather predictor by rural communities in Central Europe. In winter it can enter a state of torpor in the sediment at temperatures below 5°C.

Life Cycle & Reproduction

Sexual maturity is reached at 2–3 years of age. Reproduction takes place between April and June when water temperature exceeds 12°C, with peak intensity at 15–18°C. Fish migrate toward shallow areas with abundant aquatic vegetation for egg deposition. Females deposit 50,000–150,000 sticky eggs on submerged aquatic plants, in multiple batches. Fecundity is high, compensating for the large mortality in the first years. Incubation lasts 5–8 days at optimal temperatures. Growth is moderate — in the first year individuals reach 8–12 cm, reaching maturity in their second or third year. Maximum lifespan is 8–10 years under favorable conditions.

Conservation Status

The weatherfish is classified as Least Concern (LC) by the IUCN globally, but the situation varies significantly at regional level. In Germany, Austria, and the Czech Republic it is considered threatened or vulnerable due to habitat destruction through marsh drainage and river channelization. In Romania it is relatively abundant and is not protected under Government Emergency Ordinance 57/2007, allowing it to be captured and used as live bait. The main threats are: draining of marshes and ponds for agriculture (loss of main habitats), extreme eutrophication, pollution with toxic substances that destroy benthic fauna, and accelerated silting of lowland lakes. The ecological role of the weatherfish is important: it processes organic detritus in extreme marsh habitats, contributes to the nutrient cycle, and serves as a food source for shallow-water species.

Sources

  • FishBase: Misgurnus fossilis
  • Wikipedia: Weatherfish (Misgurnus fossilis)
  • IUCN Red List: Misgurnus fossilis