Weather loach (Misgurnus anguillicaudatus)

Synonyms: Cobitis anguillicaudata, Misgurnus mizolepis

Common Names: Oriental weatherfish, oriental weatherloach, Japanese weatherfish, pond loach, dojo loach, Chinese weatherfish

Description:

Weather loach (Misgurnus anguillicaudatus) is a small, eel-shaped freshwater fish native to eastern Asia [1][2]. It is sold widely in the aquarium and live-bait trades, and released or escaped fish have set up wild populations in waters across the United States, including the Midwest [1]. MISIN tracks it because it burrows into muddy bottoms, survives in water too low in oxygen for most fish, and can crowd out and feed on the small bottom life that native fish depend on [1][2][3].

Identification:

Weather loach has a long, rounded, eel-like body that is usually brown with darker gray-brown marbling on top and a pale silver belly [1][2]. Most are about the length of a pencil, 4 to 8 inches (10?20 cm) long, though large ones reach close to a foot (about 28 cm) [1]. Around its small, downturned mouth it carries several fleshy, whisker-like feelers called barbels ? the single best feature for telling it apart from native fish [1]. The species earns its name from its habit of swimming about wildly when the weather changes; a drop in air pressure before a storm often sets it darting around [1][2]. Because it lives on the bottom and burrows into mud, it is easiest to find when shallow ponds, ditches, or slow streams are drained, seined, or disturbed during the warmer months [1].

At-a-glance cues:

1. Long, rounded, eel-like body, brown with darker marbling and a pale belly [1][2]
2. Several whisker-like barbels around a small, downturned mouth ? native eels and lampreys have none [1]
3. Pencil-sized at 4?8 inches (10?20 cm), rarely up to about a foot (28 cm) [1]
4. Often surfaces to gulp air and darts around erratically when air pressure drops before a storm [1][2]

Habitat:

Weather loach lives on the bottom of still or slow-moving fresh water ? ponds, ditches, swamps, lake edges, the quiet stretches of rivers, and flooded fields [1][2]. It favors shallow, low-flow water with soft muddy or silty bottoms and beds of underwater plants [1]. It is unusually tough. The fish can gulp air at the surface and pass it through its gut, which works as an extra breathing organ, so it survives in warm, stagnant water that holds too little oxygen for most fish [1][2]. It tolerates water from near freezing up to about 100 ?F (38 ?C), and can ride out drought by burrowing into damp mud and going without food for weeks [1][2]. Native to eastern Asia ? from Siberia south to Vietnam, including China, Korea, and Japan ? it now has established wild populations in many U.S. states, among them Michigan and Illinois in the Midwest [1][2].

Reproduction:

Most weather loach arrive in new waters by way of people, not on their own [1][2]. The two main routes are aquarium owners dumping unwanted pets and anglers tipping out leftover live bait, since the fish is sold for both [1][2]. Once in a connected waterway it can spread on its own into ponds, ditches, and flooded fields [2]. Cleaning, draining, and drying boots, nets, and boats between waters keeps it from hitchhiking to the next site.

Females are larger than males and lay eggs many times through a long season that runs from spring into fall [1]. A single female can carry anywhere from a few hundred to many thousands of eggs ? counts of 150 to roughly 18,000 have been recorded [1]. This high output, paired with the fish's hardiness, lets a population build quickly once it takes hold [1][2]. To curb spread, the most useful step is timing ? remove fish from a small, contained pond before the spring-to-fall spawning season gets underway.

Impact and Damage:

Weather loach is not known to harm people or pets, and it is not a garden or crop pest ? its trouble is in the water [1]. Its main effect is on the small creatures that live on the bottom: in controlled experiments, the fish sharply reduced the numbers and total weight of aquatic insects, worms, and other invertebrates that native fish rely on for food [3]. By rooting and stirring up the bottom, it also clouded the water and raised nitrogen levels such as ammonia and nitrate in those experiments, which can lower water quality [3]. In U.S. waters it is expected to compete with native bottom-feeders for food and shelter, including native mudminnows where the two overlap, and it may eat the eggs and young of other fish [1][2]. Because it survives low oxygen and disturbance better than many natives, it can persist and dominate in degraded waters where native fish struggle [1][2].

Similar species:

No native loaches live in the MISIN region, so a thin, eel-shaped fish in muddy shallows is worth a close look. A few native fish are mistaken for the weather loach.

American eel (Anguilla rostrata) is the closest match in body shape ? long and snake-like ? but it grows far larger, often several feet, and has a smooth mouth with no barbels. Its dorsal, tail, and anal fins join into one continuous fin around the rear of the body, which the weather loach lacks [1].

Lampreys (such as the native American brook lamprey, Lethenteron appendix, and the wormlike young of lampreys that burrow in stream mud) are also eel-shaped and live in soft bottoms. They are easy to separate up close: a lamprey has a round, jawless sucking mouth, a row of seven small gill holes along each side, and no paired fins or barbels [1].

Madtoms (small native catfish in the genus Noturus, such as the tadpole madtom) also feel about the bottom with whisker-like barbels, which can cause confusion. But a madtom has a broad, flattened catfish head, a small fleshy fin on its back called an adipose fin, and sharp spines near the gills, while the weather loach is more uniformly slender and eel-like [1].

Central mudminnow (Umbra limi) shares the same muddy, low-oxygen habitat and can also gulp air, so the two turn up in the same places. The mudminnow is much shorter and stockier with a rounded tail and, like the eel and lamprey, has no barbels around its mouth [1].

Monitoring and rapid response:

Signs to watch for:

1. A slender, eel-like, brown fish with whisker-like barbels turning up in a pond, ditch, water garden, or slow stream [1]
2. Bottom-dwelling fish surfacing to gulp air in warm, stagnant, or low-oxygen water [1][2]
3. Fish darting around erratically when air pressure drops ahead of a storm ? the behavior behind the name [1][2]
4. Easiest to detect in the warmer months when shallow water is drained, seined, or stirred up [1]

What you can do:

1. Never release aquarium fish or leftover live bait into any pond, stream, ditch, or storm drain ? this is the main way the fish spreads [1][2]
2. In a small, contained backyard or ornamental pond, you can drain it down and remove fish by hand or dip net; do this before the spring-to-fall spawning season when possible [1]
3. Put captured fish in the trash, sealed ? never tip them into another waterway or down a drain [1]
4. Clean, drain, and dry boots, nets, buckets, and boats before moving between waters so fish and eggs do not hitch a ride [1][2]
5. Natural area crews can seine or drain isolated ponds and target small, outlying populations first, before the fish reaches connected waters, and coordinate removal across a watershed [1][2]

When to call a professional:

1. The fish is established in a natural stream, lake, or any connected water body that cannot simply be drained ? contact your state natural resources agency or a land manager [1]
2. Large or well-established populations in public waters, where coordinated removal or specialized aquatic methods are needed [1][2]
3. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. U.S. Geological Survey, Nonindigenous Aquatic Species Database. Misgurnus anguillicaudatus (Oriental weatherfish / pond loach) ? Species Profile. nas.er.usgs.gov
2. IUCN/ISSG Global Invasive Species Database (GISD). Misgurnus anguillicaudatus. iucngisd.org
3. Keller RP, Lake PS (2007). "Potential impacts of a recent and rapidly spreading coloniser of Australian freshwaters: Oriental weatherloach (Misgurnus anguillicaudatus)." Ecology of Freshwater Fish 16(2):124?132. semanticscholar.org
4. U.S. Fish & Wildlife Service. Oriental Weatherfish (Misgurnus anguillicaudatus) ? Species Profile. fws.gov

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