Weather loach

Quick facts

Adult size

20 cm

Lifespan

can live up to 10 years; long-lived; 7-10 years is routine

Tank zone

bottom

Temperament

peaceful

Difficulty

beginner

Schooling

recommended 3+ (critical minimum 2, thrives at 5+)

Water parameters

Temperature

5–25°C

pH

6.5 to 8.0

Hardness

5 to 20 dGH

Tank requirements

Minimum volume

200 L

Minimum length

100 cm

Flow

low

Lighting

dim preferred

Substrate

sand

Hiding spots

needed

Lid

required - jumper

Feeding

Diet: omnivore, feeds primarily at the bottom.

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.

Vegetable matter required (algae wafers, blanched zucchini, spinach).

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.

Habitat

Native to still and slow-moving freshwater across a vast range: Japan, Korea, China, Myanmar, and mainland Southeast Asia. Found in rice paddies, ponds, ditches, streams, and river floodplains over muddy or sandy substrates. The species (Misgurnus anguillicaudatus) was described by Cantor in 1842. The 'weather' common name comes from the observation that these loaches become notably active and agitated before storms, presumably detecting changes in barometric pressure. This behavior is well documented in aquariums: before a weather front, weather loaches swim erratically, thrash at the surface, and generally act unsettled. The body is elongated and eel-like, olive to gold-brown with variable dark mottling. A gold variant is commonly available. Adult size is 20–25 cm, occasionally larger. They breathe atmospheric air through a modified intestine; you'll see them dash to the surface and gulp air, then expel it through the vent. This is normal, not a sign of low oxygen. The species is also sold as 'dojo loach.' In some regions, it's a food fish. Invasive populations exist in Australia, North America, and Europe from released aquarium and bait fish.

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

This species is suited to outdoor ponds, not just indoor aquariums.

Climate classification

temperate

Outdoor pond zones (USDA)

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

Outside the zone range, this species can still be kept indoors. Within the zone, an outdoor pond at least 60 cm deep usually has enough thermal mass to overwinter the species, though local frost depth and surface freezing matter.

Bioload

Bioload coefficient: 5.0 (large eel-like body with active foraging; high absolute waste output).

Bioload coefficients are calibrated against the neon tetra as the anchor (1.0). See the methodology page for the formula and how each value was derived.

Further reading

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