Fork-tailed Yunnan loach

Where they come from

Fork-tailed Yunnan loaches (Yunnanilus forkicaudalis) come from cool, clear streams up in Yunnan, China. Think shallow water, lots of rock and gravel, steady current, and seasonal swings. That backstory explains why they act "picky" in the average warm community tank - they are basically built for flow and oxygen.

Setting up their tank

Give them a footprint more than a tall tank. A 20 long can work for a small group, but bigger makes life easier because you can keep the water stable and spread out territories. I like 30-40 gallons if you want a real "stream" layout.

• Substrate: smooth gravel and mixed pebbles, with a few sand patches (they graze and poke around).
• Hardscape: rounded stones, cobbles, and a couple pieces of wood for cover. Build little breaks in the flow so they can rest.
• Plants: optional, but stick to tough stuff (Anubias, Java fern, Bolbitis) tied to rocks/wood. Moss in crevices is great.
• Flow: strong enough that you see debris moving toward the intake, but not a constant hurricane everywhere. Create fast and slow lanes.
• Filtration: oversized sponge + canister/HOB. I run extra mechanical filtration because these tanks collect fine grit.
• Temperature: cool to mid-range. I keep them around 68-74F and avoid long stretches above the mid-70s.
• Water: neutral-ish is fine if its clean. Stable parameters matter more than chasing a number.

I also strongly recommend a tight lid. They are not famous jumpers like some loaches, but startled fish in high-flow tanks do weird things, and gaps around tubing are exactly where they find trouble.

What to feed them

They are micro-predators and pickers. In my tanks they spend the day grazing biofilm and tiny bits, then get bold at feeding time. The mistake is feeding only flakes and calling it done - they stay thin and never really color up.

• Staples: small sinking foods (micro pellets, crushed wafers) that break up and scatter between stones.
• Frozen: daphnia, cyclops, baby brine, chopped bloodworms (not as the only food), and small mysis for larger adults.
• Live: baby brine and grindal worms are like a cheat code for conditioning and bringing shy fish out.
• Grazing: let some rocks get a little "seasoned" with algae/biofilm. They actually use it.

How they behave and who they get along with

They are not bulldozer loaches. Most of the time they are busy hovering and picking at surfaces, with little spurts of chasing in the lower half of the tank. In a group they are more confident and you see more natural behavior.

• Group size: aim for 6+ if you can. Smaller groups can get a bit twitchy or one fish becomes the punching bag.
• Tankmates that work: other cool-water, current-loving fish that are not aggressive at the bottom (small danios, white clouds in cooler setups, some small barbs, certain hillstream loaches if the tank is big enough).
• Tankmates to avoid: big, pushy bottom feeders (large loaches, big Cory groups in a small tank), fin-nippers, and warm-water fish that want 78-80F.
• Territory: they like to claim a rock or crevice. Add more hardscape than you think you need.

Breeding tips

They can be bred, but its not a "throw them in a tank and wake up to babies" fish. What worked best for me was treating them like seasonal spawners: heavy feeding, lots of clean water changes, and a mild temperature swing.

• Setup: a separate tank with the same flow/oxygen as the main tank, fine-leaved plants or moss, and piles of small stones.
• Conditioning: 2-3 weeks of live/frozen (baby brine, daphnia, grindal worms) with frequent water changes.
• Trigger: a slightly cooler water change after a warm spell often got them displaying more.
• Egg safety: adults will snack on eggs/larvae. If you see spawning behavior, move the adults or move the egg-covered moss/stone to a rearing box/tank.

Fry are tiny and need infusoria-type food first, then baby brine. A mature tank with lots of micro-life makes the early days way less stressful.

Common problems to watch for

• Slow wasting/skinny fish: usually not enough food hitting the bottom, or the tank is too warm/low oxygen.
• Gill stress: hanging in the flow, rapid breathing, hiding more than usual. Often points to low dissolved oxygen, dirty filter, or high organics.
• Bloat after rich foods: they will overeat bloodworms. Mix in daphnia and smaller foods and do not make bloodworms the main course.
• Ich and other parasites after import: they can arrive stressed. Quarantine helps a lot, and I prefer gentle, oxygen-friendly treatments with extra aeration.
• Mysterious losses in "clean" tanks: look at flow and oxygen, not just ammonia/nitrite. A tank can test fine and still feel stale to stream fish.

If you want a quick sanity check: if your glass and rocks never grow any biofilm and you rarely have to rinse mechanical media because it stays spotless, the tank is probably too "sterile" for their grazing style. On the flip side, if detritus piles up behind rocks, increase flow and tighten up maintenance so it does not turn into a nutrient soup.