Weather Loach / Dojo Loach (Misgurnus anguillicaudatus)

Choose a peaceful, burrowing weather loach for a cool indoor aquarium

The Weather Loach, also sold as the Dojo Loach or Oriental Weather Loach, is Misgurnus anguillicaudatus, a long, slim, bottom-dwelling loach from eastern Asia. It is not a tropical fish. It comes from Siberia, Sakhalin, Korea, Japan and China south to northern Vietnam, where it lives in shallow, slow rivers, swamps, backwaters and paddy fields with soft mud, leaf litter and dense plants. FishBase calls it the pond loach. Its weather-loach name comes from its habit of becoming restless when the air pressure changes before a change in the weather.

Please read this first: this fish is for indoor aquaria only. It must never be put into a garden pond, river, stream or lake, or released anywhere in the wild. Outside its native range it has become an invasive species in parts of Europe, North America and Australia, and in England and Wales the licence that allows it to be kept covers indoor aquaria only. The UK rules are set out in full below.

Seriously Fish gives a maximum of 28 cm standard length and recommends a large aquarium with a base of at least 120 × 45 cm. It is peaceful, hardy and full of character, but it is a big fish for a big tank, not a small "cleaner" for a community aquarium.

Decide from the complete care picture

Browse our other loaches and oddball fish and the full loaches and algae eaters category. Our photographs are representative images of this species, not the individual fish supplied.

Keep it indoors: never release a weather loach

Seriously Fish describes the weather loach as exceptionally hardy and adaptable, with high reproductive potential. It reports introduced populations in Germany, Spain, Italy, Kazakhstan, Uzbekistan, Turkmenistan, the Philippines, the USA including Hawaii, Canada and Australia. FishBase lists it as a potential pest and notes that at least one country reports harm to the environment after its introduction.

In Australia, the Queensland government lists the Chinese weatherfish (this species) as a restricted noxious fish. It says wild populations exist throughout New South Wales, the Australian Capital Territory and Victoria, that the fish competes with native fish for food and space, can introduce disease and degrade habitats, and that fish reach waterways after being released from aquariums or escaping from ornamental ponds. Seriously Fish is more cautious, saying there is no proof yet of harm to native fish outside its range; the sources disagree on the evidence, but they agree that it spreads.

The same traits that make it easy to keep are the ones that let it survive outside. It tolerates about 5–25°C, can breathe air through its gut and skin when the water is short of oxygen, and buries itself in mud.

Know what UK law and guidance say

In practice that means four simple rules. Keep it in an indoor aquarium. Never put it, or its eggs or fry, in a garden pond, even for the summer. Never tip a tank containing it into a pond, stream or outside drain. If you can no longer keep it, ask a local aquatic shop or fishkeeping club to rehome it rather than letting it go.

Know what you are buying

One purchase quantity supplies one live Weather Loach in a medium-large size grade. The grade describes the fish at dispatch, not its adult size, and the sex is not specified. This listing is the natural golden-brown form with small dark speckles along the body and fins and long, sensitive barbels around the mouth.

Seriously Fish notes that xanthic "golden" and leucistic "pink" or "piebald" forms are also traded and need exactly the same care. It also warns that hybrids with the related Paramisgurnus dabryanus are produced in China and may reach the aquarium trade, so a "weather loach" from any source is best treated as needing the same cool, indoor, never-release care.

Tell males from females as they mature

• Females are heavier-bodied and slightly larger.
• Mature males have enlarged pectoral fins with a thickened second ray, a rounded plate called the lamina circularis.
• Males also develop horizontal swellings behind the dorsal fin, which you can see from above.

Young fish cannot be sexed reliably, so plan any group without counting on a particular mix.

Plan the aquarium around a 28 cm adult

Seriously Fish gives a minimum base of 120 × 45 cm, about 243 litres. Seriously Fish and FishBase both record a maximum of 28 cm standard length, OATA says weather loaches can reach up to 25 cm, and FishBase gives 15 cm as a common length. Plan for the larger figure: a fish that may end up around the length of a school ruler needs floor space to turn, dig and rest.

Floor area matters more than height for a bottom-dweller. A long, wide aquarium gives each loach room to burrow and gives tank mates open water above, while a tall, narrow tank wastes volume where the loach will rarely go.

Use a three-step space check

1. Measure the base: at least 120 cm long and 45 cm from front to back.
2. Count every adult: each weather loach at up to 28 cm, plus every tank mate at its adult size.
3. Allow for the group: the 120 × 45 cm figure is a minimum for the species; three adults, as OATA recommends, and their companions need more floor space.

Our aquarium volume calculator turns your tank's dimensions into litres, and our stocking calculator helps you check the adult population before you buy.

Lay soft sand and smooth hiding places

Weather loaches spend a lot of time digging, and often bury themselves completely with only the head showing. Seriously Fish recommends soft sand or fine gravel, because coarse material can stress or injure them, and OATA notes that their skin is sensitive, so sharp or rough ornaments are not suitable.

Divide the footprint by function

Seriously Fish suggests fairly dim lighting unless you are growing plants. If you add plants, choose hardy ones and anchor them well or attach them to wood and rock, because a digging loach will uproot anything loosely planted in the sand.

Keep the water cool, not tropical

Seriously Fish recommends 18–23°C, pH 6.0–8.0 and 1–12 dGH, and says the fish reportedly tolerates 5–25°C. OATA gives 17–24°C, pH 6.5–8.0 and 4–12°dH. The ranges overlap well: aim for a steady 18–23°C with pH 6.5–8.0 and soft to medium hardness.

In a heated home an indoor aquarium often sits in that range without a heater, but measure it rather than assume. A tank in a warm room in summer can climb above 23°C, and one in an unheated room can fall below 18°C in winter. Our water matcher checks your tap-water readings against the range, and the guide to aquarium water chemistry explains pH and hardness.

Separate habitat values from waste readings

The waste limits come from OATA's unheated aquarium guide. A weather loach can survive poor water in the wild, but surviving is not thriving: in an aquarium, waste builds up in the sand where it lives, so keep those readings at the limits above.

Filter well but keep the flow gentle

Seriously Fish advises avoiding strong flow but providing some oxygenation, and never adding this fish to a biologically immature aquarium. Use a well-established filter sized for the adult stock, with the outflow spread across the surface rather than blasting across the sand, and cover the intake with a guard or sponge.

Follow a weekly maintenance sequence

1. Test ammonia, nitrite and nitrate before you start.
2. Change at least 25% of the water each week, treating new water with a dechlorinator and matching its temperature.
3. Siphon the sand surface gently, without digging out the loaches or exposing the whole bed.
4. Check the filter intake guard and flow.
5. Rinse filter media only in water taken from the aquarium, never under the tap.

Our nitrogen cycle guide explains how a new aquarium matures and why a weather loach should only go into a tank that is already established.

Feed sinking foods and regular frozen treats

In the wild the weather loach feeds mainly on insect larvae and small crustaceans, and FishBase adds worms and other small aquatic animals. Seriously Fish says it accepts sinking dried foods but should regularly get live or frozen foods such as Daphnia, brine shrimp and bloodworm for a varied diet. OATA describes it as omnivorous and recommends a good-quality sinking catfish pellet.

Build one measured meal

• Staple: a sinking pellet or granule for bottom fish, such as Welsi Gran sinking bottom-fish food.
• Frozen and live foods: frozen Daphnia, brine shrimp or live bloodworm several times a week.
• Placement: drop food where the loaches can reach it before faster fish above take it all.
• Portion: only what the fish clear within a few minutes; remove leftovers from the sand.

If busy tank mates eat everything first, split the same daily amount and give part of it shortly after the lights go out, when the loach can feed undisturbed. Keep the total amount the same: uneaten food hidden in sand rots quickly.

Introduce it to a mature aquarium

Before the loach arrives, confirm that the filter is mature, ammonia and nitrite read zero, the temperature is 18–23°C and the lid closes fully. Float the sealed bag for about 10 minutes with the lights off, add small amounts of aquarium water over up to 20 minutes, then net the fish into the tank and discard the bag water. Expect it to bury itself or hide for the first few days.

Use a first-week checkpoint plan

For more detail, follow our step-by-step guide to acclimatising new fish, and check our delivery and live arrival terms so you can be at home on the day.

Watch for problems and act on them

A healthy weather loach has intact barbels, smooth skin, clear eyes and a good appetite. Some behaviour that looks odd is normal: burying itself with only the head showing, becoming restless when the air pressure changes, and an occasional dash to the surface to gulp air.

Pair each observation with an action

Keep weather loaches together

Seriously Fish says the weather loach can be kept alone but is more settled and active with others of its kind. OATA describes it as a social species and recommends groups of at least three so they can interact. A group digging and resting together is one of the best things about keeping them, but only plan for it if the floor space allows three adults.

Read the breeding notes before you plan a group

Seriously Fish says reports of captive breeding are scarce and short on detail. In the wild it probably breeds like the European weatherfish: first spawning at two to three years old and about 11 cm, between March and July, with the male coiling around the female in dense plants as she releases eggs. The fry have external gill filaments that disappear after 10–12 days. That high breeding potential is one more reason the fish, its eggs and its fry must never reach a pond or the wild.

Choose tank mates that swim higher in the water

Seriously Fish describes the weather loach as peaceful with its own kind and other species, and says it does best with medium to large, active fish that stay higher in the water. It may eat eggs, fry and very small fish, and because it hunts small crustaceans in the wild, dwarf shrimp are at risk too.

Use the same screening questions every time

Single-tailed goldfish grow large too, so the aquarium must suit their adult size as well. Our comet goldfish guide covers their needs, and you can browse more coldwater companions in our goldfish and coldwater fish range. The Stone Loach is another loach for cool water, but it is a European river fish that needs faster, well-oxygenated flow, so it is not a natural partner for a weather loach set-up.

Answer weather loach buying questions

Is it legal to keep a weather loach in the UK?

Yes, indoors. In England and Wales the government list of freshwater fish kept under a general licence includes Misgurnus anguillicaudatus, and that licence allows keeping in indoor aquaria only. It is an offence to release it into the wild anywhere in Great Britain.

Can I put a weather loach in my garden pond?

No. The general licence covers indoor aquaria only, OATA says it is not legally permitted outdoors, and Seriously Fish says it should never be kept outdoors. It has been introduced and has spread in the wild in parts of Europe, North America and Australia.

Does a weather loach need a heater?

Usually not in a heated home. Seriously Fish recommends 18–23°C and OATA 17–24°C. Measure the water: use a heater only if the room drops below that range, and cool the tank if summer heat pushes it higher.

How big do weather loaches get?

Seriously Fish and FishBase both give a maximum of 28 cm standard length; OATA says up to 25 cm, and FishBase gives 15 cm as a common length. Plan for the larger figure.

What size tank does a weather loach need?

Seriously Fish gives a minimum base of 120 × 45 cm, about 243 litres, with soft sand, smooth hiding places and a tight-fitting lid. A group needs more room than that minimum.

How many weather loaches should I keep?

OATA recommends at least three. Seriously Fish says one can live alone but is more settled and active with others of its kind. Each purchase quantity supplies one fish.

Can a weather loach live with goldfish?

It suits active coldwater fish such as comet and wakin goldfish. Seriously Fish warns it can disturb slow fancy goldfish at feeding time, and it may eat eggs, fry and very small fish.

Why does my weather loach dash about or gulp air?

Restless activity when air pressure changes gave it the name weather loach. It can also breathe air through its gut and skin, so an occasional gulp is normal; frequent gulping means you should test the water and add aeration.

Consult the care and legal references

• Seriously Fish: Misgurnus anguillicaudatus — names, native and introduced range, habitat, maximum length, minimum aquarium, décor, water range, diet, behaviour, sex differences, breeding, colour forms and the "never outdoors" advice.
• FishBase: Misgurnus anguillicaudatus — family, maximum and common length, temperature tolerance, distribution, introductions, wild diet, air breathing and pest status.
• OATA: Indoor coldwater fish, how to care for unheated aquarium inhabitants (September 2022) — UK trade guidance on weather loaches: size, group size, skin, feeding, water values and the rule that these fish must be kept indoors only.
• GOV.UK: Introduce or keep non-native fish and shellfish — licensing of non-native fish in England and the link to the list of fish that may be kept in indoor aquaria.
• GOV.UK: Freshwater fish that can be kept for ornamental purposes (list updated 13 October 2026) — lists the genus Misgurnus with only M. anguillicaudatus and M. mizolepis, under a general licence for indoor aquaria only.
• Wildlife and Countryside Act 1981, section 14 — offence of releasing, or allowing to escape into the wild, an animal not ordinarily resident in Great Britain (Scotland has its own version).
• Business Queensland: Chinese weatherfish — legal status as a restricted noxious fish in Queensland, impacts on native fish and spread from released aquarium fish and ornamental ponds.
• Tropical Fish Co delivery policy — current dispatch days and live arrival terms.