Small Yunnan loach

Where they come from

Small Yunnan loaches (Yunnanilus parvus) come from cool, clean streams and springs around Yunnan in southwest China. Think shallow water, lots of oxygen, and a bottom full of gravel, pebbles, and leaf bits. They are one of those fish that look plain in a store tank, then turn into little gems once you give them the right setup.

Setting up their tank

They do best in a tank that feels like a stream, not a planted pond. You want lots of surface movement, clean water, and plenty of small hiding spots. I have had the best results keeping them in a mature tank with stable parameters and a bit of biofilm already going.

• Tank size: 10-20 gallons works for a small group, but bigger is easier to keep stable
• Substrate: smooth sand or fine gravel so they can root around without scraping themselves up
• Hardscape: rounded stones, small cobbles, driftwood, and piles of leaf litter in a corner
• Plants: optional, but tough stuff like Java fern, Anubias, moss, and floating plants work well
• Flow and oxygen: a strong filter, powerhead, or airstone - aim for ripples everywhere
• Lighting: moderate is fine; a bit of algae and biofilm is your friend

Water-wise, cool to mid temps are where they settle in and act natural. I keep mine in the low 60s to low 70s F (about 17-22 C) depending on the season. Neutral-ish pH is usually fine, but the big thing is cleanliness and oxygen. They really do not forgive neglected maintenance.

What to feed them

They are micro-pickers. In a good tank they graze all day, grabbing tiny worms, crustaceans, and whatever is living in the gunk on rocks and leaves. If you only feed big pellets, they will look like they are eating... and then slowly get skinny.

• Staples: small sinking foods (micro pellets, crushed wafers) that break up easily
• Frozen: cyclops, daphnia, baby brine, chopped bloodworms (small portions)
• Live: baby brine shrimp, grindal worms, microworms, blackworms (if you trust the source)
• Extras: Repashy-style gel foods smeared on a stone can work great for grazers

I watch their bellies more than their enthusiasm at feeding time. A healthy group has slightly rounded bellies most days. If you see hollow-looking sides, bump up tiny live/frozen foods and check if faster tankmates are stealing everything.

How they behave and who they get along with

They are peaceful, busy little fish. Most of the "drama" is harmless posturing and short chases, usually around favorite hiding cracks or food. In a small group they are way less skittish, and you get to see more natural foraging.

• Group size: 6+ is a good starting point if your tank can handle it
• Good tankmates: other cool-water, calm fish that like flow (small danios, white clouds, some minnows), and gentle bottom dwellers that will not bulldoze them
• Use caution: bigger loaches, aggressive barbs, or anything that competes hard for the bottom
• Avoid: warm-water community mixes, fin nippers, and large predators

They are also surprisingly good escape artists. Any gap around hoses or a loose lid is worth fixing. If they get spooked (netting, sudden lights, a big fish thumping around), they can launch.

Breeding tips

Breeding them in home tanks is possible, but it is one of those "it happens when the tank is right" situations. The best odds come from a settled group, heavy conditioning on small live/frozen foods, and seasonal cues.

• Conditioning: 2-4 weeks of daily small live/frozen feedings (daphnia, baby brine, cyclops)
• Cue changes: slightly cooler water and larger water changes can trigger activity
• Spawning sites: fine-leaved moss, leaf litter, and tight rock gaps
• Egg and fry safety: adults may snack, so mossy/leafy cover helps a lot

If you do get fry, they are tiny and need tiny foods. Think infusoria-style first foods, then baby brine shrimp as soon as they can take it. Clean water matters even more at this stage, but go gentle on the flow so they are not pinned around the tank.

Common problems to watch for

Most issues with Yunnanilus parvus come from warm, stale water, or from them slowly wasting away because they are not getting enough small food. They can look "fine" right up until they are not, so little check-ins go a long way.

• Skinny fish: usually food competition or food size being too big (add small live/frozen and spread feeding spots)
• Gasping or hanging in high flow: oxygen is low or the tank is dirty (increase surface agitation, check filter, water change)
• Sudden losses after purchase: stress plus immature tank or swings in temperature (slow acclimation, stable cool temps, mature biofilter)
• Scrapes and red marks: rough decor or sharp gravel (switch to smoother substrate/rocks)
• Ich and other stress illnesses: often triggered by swings and crowding (stabilize temps, improve water quality, treat carefully)

My routine that keeps them looking good is simple: cool, clean, high-oxygen water; lots of hiding cracks; small foods they can actually swallow; and a group big enough that no single fish gets picked on. Do that, and they turn into confident little foragers instead of "mystery fish that disappear."