Caohai stone loach

Where they come from

Caohai stone loaches (Eonemachilus caohaiensis) come from a pretty specific corner of China around Caohai Lake, where the water stays cool and oxygen-rich and the bottom is all rock, gravel, and leaf litter. Think shallow edges, current, lots of hiding cracks. If you set up your tank to feel like that, you are halfway there.

Setting up their tank

I treat these like a small river fish. Give them footprint more than height. A 20 long can work for a small group, but bigger is honestly easier because stability and territory issues get less dramatic.

• Tank size: 20 long minimum for a small group, 30-40 breeder is nicer
• Footprint matters more than depth
• Keep them in a group (4-8) so one fish does not take all the heat

Substrate and hardscape are a big deal. They spend their day on the bottom and under things. I like a mix of smooth sand and rounded pea gravel, plus lots of fist-sized river stones and slate pieces stacked to make tight crevices. Driftwood roots also work if you can wedge them to form little tunnels.

Flow and oxygen are where most people miss. A strong filter with a spray bar pointed along the back glass, or a powerhead aimed down the length of the tank, makes them act way more natural. Keep the surface churning. If your tank ever looks "still," they will tell you by acting listless and hanging in the easiest-flow spot.

• Temperature: cool to mild (roughly 18-22 C / 64-72 F is where I have had the best results)
• Oxygen: high (surface agitation, decent turnover, no stagnant corners)
• Water quality: very clean, low nitrate, consistent parameters

Lighting can be moderate, but give them shade. Floating plants or taller plants along the edges help. They are not plant-eaters, but they will bulldoze delicate stems while foraging, so pick tough stuff (Crypts, Java fern, Anubias, mosses wedged into rocks).

What to feed them

They are micro-predators and scavengers, not algae grazers. Mine go nuts for anything meaty that sinks and fits their little mouths. If you only offer flakes at the surface, you will think they are shy or not eating. They are just waiting for food to hit the bottom.

• Staples: sinking micro-pellets, small sinking wafers with higher protein
• Frozen: bloodworms, brine shrimp, daphnia, chopped blackworms
• Live (if you can): grindal worms, blackworms, live daphnia
• Occasional: gel foods or repashy-style mixes pressed into crevices

I do small portions more often rather than one big dump. They hunt all day in nature, and heavy feedings can foul the water fast in a rockscape. One fast day a week also helps keep the tank cleaner and the fish lean.

How they behave and who they get along with

Personality-wise they are classic stone loach: curious, twitchy, always inspecting cracks. Not aggressive like some bigger loaches, but they do sort out a pecking order. You will see little shoving matches and "face-offs" in favorite hiding spots.

• Best kept with: other cool-water, current-loving fish
• Good tankmates: small danios, white cloud mountain minnows, hillstream loaches (with enough space), small barbs that like cooler water
• Avoid: slow long-finned fish, warm-water community fish, big boisterous bottom fish (they will get outcompeted)

They are masters at getting into places you did not design for fish. Any gap in a lid, any open filter intake, any loose rock pile will get tested. Once they settle in, they are not as jumpy, but new imports can bolt.

Breeding tips

Breeding in home tanks is possible but not something I would call consistent. The big hurdle is getting a settled group through seasonal cues: cooler period, then gradual warm-up and heavier feeding, plus lots of micro-habitat (gravel pockets, rock crevices, and plants or moss).

• Keep a group so you have both sexes (sexing is not always obvious)
• Simulate seasons: cooler, leaner period then a slow warm-up with more food
• Add spawning media: fine gravel areas, moss clumps, leaf litter pockets
• Watch for eggs in crevices and under stones

If you ever see a sudden spike in chasing and the fish working one area of the substrate, check that spot later with a flashlight. If you get fry, they need tiny foods right away (infusoria, rotifers, baby brine later). Also, adults will snack on eggs and fry if they find them, so a separate rearing setup helps.

Common problems to watch for

Most issues with Caohai stone loaches come down to three things: too warm, not enough oxygen/flow, and not enough food making it to the bottom. They can look "fine" for weeks, then slowly fade because they are stressed and underfed.

• Thin belly or pinched look: getting outcompeted at feeding time or not enough sinking foods
• Hanging near the surface or filter output: chasing oxygen (check temperature, flow, and surface agitation)
• Hiding nonstop for weeks: too bright, too exposed, too much traffic from tankmates, not enough tight cover
• Scrapes and nicks: rock piles shifting, sharp decor, or constant territory pressure

Quarantine is worth the effort. Wild-caught or recently imported loaches can come in skinny with internal parasites. If a fish eats but never fills out, that is a clue. Also be gentle with meds: they are scaleless-ish and can react strongly. I stick to proven dosing, extra aeration, and I avoid stacking multiple treatments at once.