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 eats anything that reaches the bottom. Sinking pellets, frozen bloodworm, frozen brine shrimp, blanched vegetables, live blackworms, live earthworm pieces. They forage by rooting through the substrate, sometimes burying themselves completely and surfacing elsewhere. Feed once or twice daily. In community tanks with goldfish, they eat whatever the goldfish miss. They're not competitive feeders but they're thorough; given time, they find everything.

Compatibility

• One of the most personable freshwater fish. Weather loaches learn to recognize their owner, beg for food at the glass, and tolerate (sometimes seem to enjoy) being touched during tank maintenance. Their behavior is more like a pet than a typical aquarium fish.
• Peaceful with everything. They don't compete for territory, don't nip, and don't threaten even tiny tankmates. The only risk is accidental injury to very small fish during the loach's energetic burrowing and thrashing at feeding time.
• Cold-water species (10–25°C). Not a tropical fish. Best kept with other subtropical or cold-water species: goldfish, white clouds, rosy barbs, and hillstream loaches. They survive in tropical tanks (26°C+) but their lifespan shortens.
• Grows larger than expected: 20–25 cm. They need a long tank (100 cm) with soft substrate they can burrow into.

Origin and habitat

Native to eastern Asia, from Siberia south through China, Japan, Korea, and Vietnam. Described by Cantor in 1842. A member of the family Cobitidae (true loaches). Also widely known as dojo loach, pond loach, or oriental weatherfish. Found in muddy or silty substrates in low-gradient, shallow water: rice paddies, ponds, ditches, streams, and river floodplains, often in aquatic macrophyte beds. Considered a cool-water species; individuals burrow into soft substrates during dry periods and tolerate low-oxygen conditions by breathing atmospheric air through a modified intestine. The "weather" common name comes from the well-documented behavior of becoming notably active and agitated before storms, presumably detecting changes in barometric pressure; this behavior is observed in aquariums as well as in the wild. Wild fish can grow up to 30 cm, though captive specimens may only reach about 15 cm. A gold color variant is commonly available in the trade. Also valued as a food fish and for medicinal purposes in parts of its native range. Has become a major invasive species across parts of the United States, Canada, Australia, Europe, and other regions from released aquarium and bait stock.

Breeding

Not commonly bred in home aquariums, though it does happen in large outdoor tubs and ponds where the seasonal cycle can be replicated. Breeding requires a cool-to-warm temperature cycle (a winter period at 10–15°C followed by warming to 20–25°C in spring) and a large water volume. The pair embraces, with the male wrapping around the female, and eggs are scattered among vegetation. Clutch sizes are reportedly large (hundreds of eggs). Eggs hatch in 3-4 days. Fry eat infusoria and baby brine shrimp. Indoor breeding in heated tanks has been reported but is inconsistent. The species breeds readily in outdoor ponds in temperate climates, which is one reason it has become invasive outside its native range.

Common problems

Temperature mismanagement is the main issue. Weather loaches are cold-water fish kept in tropical tanks far too often. At 26–28°C they survive but their lifespan drops from 10+ years to 3-5 years. Ideal temperature is 15–22°C. Sand substrate is important; they burrow constantly and coarse gravel traps and abrades them. Jumping is a concern during periods of agitation (storms, water changes); a lid is necessary. The species is hardy and disease-resistant at cool temperatures. Ich is uncommon. They tolerate a wide range of water chemistry. The main 'problem' is that people don't expect a 25 cm loach when they buy a 7 cm juvenile, and the space requirement is larger than it appears.

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