Large-spotted Yunnan loach

Where they come from

Large-spotted Yunnan loaches (Yunnanilus macrositanus) come out of Yunnan, China. Think cool, clean hill streams and spring-fed waterways with lots of rock, gravel, and leaf litter - not warm, weedy ponds. That background explains almost everything about why they can be a bit touchy in typical community-tank setups.

Setting up their tank

These are advanced mostly because they are unforgiving about stale water and low oxygen. Give them a tank that behaves like a stream: steady flow, lots of surface agitation, and stable, clean water.

• Tank size: I would start at 20 gallons long for a small group. Bigger is easier to keep stable.
• Substrate: smooth sand or fine gravel. They spend a lot of time on the bottom and around stones.
• Hardscape: rounded river rocks, cobbles, and a few pieces of wood. Make little current breaks and crevices.
• Plants: optional. If you use them, pick stuff that handles cooler water (Anubias, Java fern, mosses).
• Filtration and flow: strong filtration plus a powerhead or spray bar. You want visible surface movement.
• Oxygen: high. Airstone is not mandatory if flow is good, but it never hurt me with this kind of fish.

For water, aim for cool-to-moderate temps and avoid big swings. They generally handle neutral-ish water fine if its clean, but they react fast to ammonia/nitrite and they do not love being cooked in the high 70s F for long.

What to feed them

They are micropredators and pickers. Mine spent the day grazing biofilm and hunting tiny stuff between pebbles, and then got more active at feeding time. You will get better results feeding smaller foods more often instead of one big dump.

• Staples: sinking micro pellets, crushed high-quality pellets, and small wafers that soften fast
• Frozen: bloodworms (sparingly), daphnia, cyclops, brine shrimp, chopped blackworms if you can get them
• Live: baby brine shrimp, grindal worms, live daphnia - they go nuts for these
• Grazing foods: repashy-style gel foods work well because they can rasp at it

How they behave and who they get along with

They are more "busy" than aggressive. Expect lots of prowling, short dashes, and little standoffs over favorite cracks between stones. In a group they look more confident, and you see more natural behavior.

• Keep in a group if you can. I like 6+ if the tank size allows.
• Best tankmates: other cool-water, current-loving fish that are not bullies (small danios, white clouds, some hillstream loaches).
• Avoid: big, pushy bottom fish (large botias, large corys in tight tanks), nippy barbs, and anything that needs warm water.
• Shrimp/snails: small shrimp may get hunted, especially babies. Snails are usually fine.

Breeding tips

Breeding Yunnanilus is possible, but its not like livebearers where it just happens. Most success stories look like this: a settled group, heavy feeding on small live/frozen foods, and then a seasonal trigger (cooler water and big water changes) that mimics spring conditions.

• Start with a group and let them pair off naturally - sexing is not always obvious.
• Use a mature tank with lots of micro-life and cover (moss, fine plants, pebble beds).
• Try a "spring" routine: slightly cooler period, then several larger water changes with fresh, cooler water and stronger flow.
• If you see spawning behavior, consider moving adults out after a day or two. They can snack on eggs and tiny fry.

Common problems to watch for

Most issues I have seen with these come down to warm, low-oxygen water, dirty bottoms, or being outcompeted for food. They can look "fine" for weeks and then start losing weight or clamping fins.

• Skinny loaches: often not getting enough food in a busy community tank. Feed after lights out or target feed with a pipette.
• Hanging near the surface or rapid breathing: not enough oxygen or too warm. Add flow, increase surface agitation, and check temperature.
• Hiding all the time: not enough cover, too much light, or tankmates stressing them out.
• Bloat after heavy feeding: ease off rich foods (like lots of bloodworms) and rotate in daphnia and smaller meals.

Quarantine matters with these. Wild or farmed imports can bring in parasites, and loaches can be more sensitive to some medications. I go slow with dosing, use extra aeration, and I avoid mixing multiple meds unless I am 100% sure what I am treating.