Large-scale Yunnan loach

Where they come from

Large-scale Yunnan loaches (Yunnanilus macrolepis) are little stream fish from Yunnan, China. Think cool, clear water running over rock and gravel, lots of oxygen, and a steady current. They are not a swampy-pond loach at all, which is why they trip people up.

Setting up their tank

Give them a footprint more than height. Mine spent almost all their time on the bottom and hardscape, picking and cruising, and they used every inch of floor space.

• Tank size: I would not bother with less than a 20 long for a small group. Bigger is easier because the water stays steadier.
• Substrate: smooth gravel, rounded pebbles, and some sand patches. Skip sharp stuff - these fish wedge themselves into places.
• Hardscape: lots of smooth stones, cobbles, and a few pieces of wood for line-of-sight breaks.
• Plants: they do fine with plants, but pick stuff that does not mind current (Anubias, Java fern, Bolbitis, mosses).
• Flow and oxygen: strong filtration and surface movement. A powerhead or river-manifold style flow makes a big difference.

Temperature matters more than most people expect. Aim for cool to low-70s F most of the time. If your fish room runs hot in summer, plan for it with extra aeration, fans, and shaded lighting. Warm water plus low oxygen is where they start going downhill.

What to feed them

They are micro-predators and pickers. In my tanks they grazed surfaces all day, then went nuts for small meaty foods. I would not treat them like strict algae/biofilm fish, but I also would not keep them on only pellets.

• Staples: frozen daphnia, cyclops, baby brine, chopped bloodworms, and good micro pellets that sink.
• Live foods: grindal worms, blackworms (if you can source clean), moina/daphnia cultures.
• Supplement: occasional Repashy-type gel foods or finely crushed flakes if they will take it.

Make sure food actually gets to the bottom. I used a turkey baster to squirt thawed frozen foods into rock piles and along the flow line. That little trick stops the midwater fish from intercepting everything.

How they behave and who they get along with

They are generally peaceful, a bit shy at first, and then surprisingly busy once they settle. In a group they show more natural behavior and come out more. Solo fish tend to stay tucked under stones and only dart out to feed.

• Best kept in groups: 6+ is a nice number if your tank size allows it.
• They do some low-key sparring and chasing, but it is usually more posturing than damage.
• They appreciate hiding spots that break up sight lines so the "boss" fish cannot see everybody all the time.

For tankmates, pick other cool-water, current-friendly fish that will not bully them or outcompete them at feeding time.

• Good options: small danios from cooler water, white clouds, some small barbs, and other mellow stream loaches if the tank is big enough.
• Use caution: super food-aggressive fish (big danios, boisterous barbs) because your Yunnanilus can get skinny without you noticing.
• Avoid: warm-water community fish, big predatory species, and anything that likes to dig constantly in the same crevices they use.

Breeding tips

Breeding them in home tanks is possible but not something I would call predictable. The biggest trigger I have seen for stream fish like this is seasonal-style changes: a cooler period, then a bump in food and a run of larger water changes with slightly cooler water.

• Keep a group with a good mix of sexes (if you can). More fish gives you better odds.
• Give them pebble piles, cracks between stones, and fine-leaf plants or moss where eggs can disappear.
• Condition with live and frozen foods for a few weeks, then do a series of cool, heavy water changes.
• If you suspect spawning, consider moving the adults or moving the rocks/moss to a fry box or small grow-out. They are not dedicated egg guards.

Common problems to watch for

Most issues with this species come from the environment, not some mysterious disease. If you nail cool, clean, oxygen-rich water and steady feeding, they are pretty hardy. If you miss those, they look fine until they suddenly do not.

• Heat stress: rapid breathing, hanging in high-flow spots, fading color, hiding more than usual. Add aeration and drop temps.
• Slow starvation: belly pinching in, fish getting timid at feeding, weight loss even though "they eat." Feed targeted bottom foods.
• Poor oxygen/dirty substrate: fish camping at the filter outflow and acting restless. Increase flow, vacuum dead zones, clean one filter at a time.
• Skin and gill issues after purchase: many arrive stressed. Quarantine helps, and keep meds gentle because loaches can be sensitive.

Last practical thing: cover the tank. They are not famous jumpers like some fish, but startled stream fish can and will launch if the lid is loose and the lights flip on suddenly.