Weather loach

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: sand.

Behavior

Plant interaction: digs up plants.

Feeding

Omnivore that takes almost anything reaching the bottom: sinking pellets, frozen bloodworm and brine shrimp, blanched vegetables, and live blackworms or chopped earthworm. It forages by rooting through soft substrate, often burying itself and resurfacing somewhere else. Activity rises toward dusk and through the night, so an evening feeding helps it get its share in a community tank. Not a competitive feeder, but methodical; given time it finds buried food the others miss.

Nocturnal feeder; drop food after lights out.

Compatibility

• One of the most personable freshwater fish. Weather loaches learn to recognize their keeper, gather at the glass at feeding time, and tolerate, even seem to welcome, gentle handling during maintenance. The behavior reads more like a pet than a typical tank fish.
• Peaceful with everything. They hold no territory, do not nip, and pose no threat even to tiny tankmates. The only real risk is accidental injury to very small fish during the loach's energetic burrowing and thrashing at feeding time.
• Cool-water species (10–24°C). Not a tropical fish. Best kept with other cool-water or subtropical fish such as goldfish. It can survive warmer tropical tanks (26°C+), but its lifespan suffers.
• Grows larger than people expect: 20–25 cm. It needs a long tank (100 cm) with soft substrate to burrow into.

Origin and habitat

Native to eastern Asia, ranging from Siberia south to northern Vietnam and including Japan, Korea, and much of China. Cantor described the species in 1842, placing it in the loach family Cobitidae (order Cypriniformes). It goes by several common names: dojo loach, pond loach, oriental weatherloach, and oriental weatherfish. The cylindrical, eel-shaped body bears five pairs of barbels around a small mouth, and color runs from yellow and olive to brown or grey, with pink, orange, and albino strains also sold. It lives in slow or still water over soft muddy or sandy bottoms: rice paddies, ponds, ditches, and floodplain margins, burrowing into the substrate to hide or wait out dry spells. The fish gulps air at the surface and absorbs oxygen through its hindgut, an enteral respiration that lets it endure low-oxygen water and survive out of water for a time. The 'weather' name reflects a long-noted habit of swimming frantically or standing on end when barometric pressure drops ahead of a storm. Wild fish reach about 25 to 30 cm, while aquarium specimens often stay nearer 15 to 20 cm. The IUCN lists it as Least Concern. It is farmed heavily for food across East Asia, turning up in Korean chueo-tang, the Japanese hotpot dojo nabe, and Sichuan cooking, and it ranks among the most farmed fishes in the world by individual count. Released aquarium and bait stock have founded invasive populations across the United States, Canada, Europe, and Australia, where it is treated as a noxious pest.

Breeding

Spawning tracks the seasons: a cool winter followed by warming water in spring brings the fish into condition, and the eggs are scattered rather than guarded. Reliable breeding in home aquariums is uncommon, though it happens in outdoor ponds and large tubs where the temperature swing occurs on its own, which is part of why the fish establishes itself so easily once released. Reproduction in this loach is unusual. Most populations are sexual diploids, but some wild populations carry all-female clonal lineages that reproduce by gynogenesis: a sperm activates the egg without contributing genetic material, so the young are genetic copies of the mother. The species is also raised at large commercial scale, so hatchery technique is well developed even where hobby spawning stays inconsistent.

Common problems

Temperature is the usual mistake. These are cool-water fish often kept in heated tropical tanks, where sustained warmth above roughly 24 C brings stress, respiratory trouble, fatigue, and a shortened life. Cooler water near 15 to 22 C suits them, which is why goldfish make good companions. Substrate matters too: they burrow constantly, and coarse or sharp gravel abrades their barbels and skin, so fine sand or smooth fine gravel is the safer choice. They are determined jumpers, especially when agitated by storms or water changes, and they will also work their way into open filter intakes or tubing, so a secured lid and guarded inlets are needed. The species is hardy and forgiving of imperfect water chemistry. The most common surprise for new keepers is size: a small youngster grows into a 20 cm to 25 cm burrower that needs a long tank and more room than expected.

Outdoor pond suitability

Climate

temperate

USDA zones

3–10 (winter low around -40°C or warmer)

Outdoor pond at least 60 cm deep for thermal mass. Local frost depth and surface freezing matter.

Bioload

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size