Mandeville's loach catfish

Where they come from

Mandeville's loach catfish (Zaireichthys mandevillei) comes from the Congo Basin region (historically called Zaire), living in small rivers and creeks with a lot of flow, smooth rock, and sand. Think shallow, oxygen-rich water where food drifts past and there are cracks and gaps to wedge into.

They are one of those fish that look like they were built for current. If you set them up like a still community tank, they usually hang on for a while... then slowly fade.

Setting up their tank

This is an advanced fish mostly because the tank has to be built around them, not the other way around. Mine did best in a river-style setup: lots of circulation, very clean water, and a bottom they can actually use without shredding themselves.

• Tank size: 20 gallons is workable for a small group, but 30+ makes everything easier (flow, territory, stability).
• Substrate: fine sand or very smooth small gravel. Skip sharp stuff - they scoot and wedge into places a lot.
• Hardscape: rounded river stones, slate, and chunks of driftwood arranged to make tight crevices and shaded lanes.
• Flow: strong. Aim for a steady laminar-ish current across the bottom, not just surface agitation.
• Filtration: oversized and oxygen-forward (good bio, lots of turnover). A sponge prefilter helps if you run strong intakes.
• Lighting: they do not need it bright. If you like plants, stick to tough stuff on rocks/wood (Anubias, Java fern, Bolbitis).

Give them lots of hiding spots that are actually "their" size. They love a crack between two stones where only a thin fish can slide in. PVC works too, but rock piles look better and they seem to use them more naturally.

What to feed them

They are small predators and pickers, built for grabbing tiny meaty things off the bottom and out of the current. In my tanks they ignored a lot of "generic bottom feeder" foods until they settled in, and even then they stayed picky.

• Staples: sinking micro-pellets, small carnivore pellets, and wafer-style foods that soften fast.
• Best frozen foods: bloodworms, blackworms, daphnia, cyclops, chopped brine shrimp, mysis (if pieces are small).
• Live foods (if you can): blackworms and grindal worms are like a cheat code for getting thin new fish eating.

Feed after lights down or at least in low light. They will come out in the open once they trust the tank, but they are still more comfortable grabbing food while the "daytime" fish are calmer.

How they behave and who they get along with

They are shy, bottom-oriented, and kind of "clingy" with structure. You will see bursts of activity, then they melt back into a crack like they were never there. Once established, they get bolder and you will catch them perched on rocks facing into the current.

I have had the best results keeping them in a small group. Singles can work, but they tend to stay hidden and you have no clue if they are doing well until it is too late.

• Good tankmates: small peaceful midwater fish that like flow (small barbs, danios, small African tetras) and calm bottom fish that will not compete too hard.
• Avoid: big boisterous feeders, fin nippers that harass anything hiding, and large cichlids that will treat them like snacks.
• Bottom competition: be careful with other fast bottom carnivores (some loaches, Synodontis, larger catfish). They can outcompete Zaireichthys at feeding time.

Breeding tips

Breeding them in a home aquarium is not common. Most people just do not see obvious spawning behavior, and sexes are not always easy to tell unless you have a mature group and a sharp eye.

If you want to take a swing at it, the best shot is copying what river fish respond to: heavy feeding on live/frozen foods, very clean water, strong oxygenation, then a cool-water water change that mimics rainy-season influx. Give them tight cave-like crevices and let them do their thing without constant disturbance.

Common problems to watch for

Most issues with this species trace back to two things: not enough oxygen/flow, and not enough food getting to them.

• Slow decline in still tanks: they may look fine for weeks, then start hiding nonstop and losing weight.
• Skin and barbels getting damaged: usually from sharp substrate, rough rocks, or getting pulled into a strong intake.
• Starvation in a community: they are small and not pushy. If you only feed one spot, they often miss meals.
• Sensitivity to dirty water: they react poorly to neglected filters and old mulm pockets in low-flow corners.

Medicating can be tricky because these are scaleless catfish. If you have to treat, go gentle, increase aeration, and avoid blasting them with strong doses right out of the gate. Quarantine new fish if you can, because once something like ich gets into a fast-flow river tank, it is a pain to manage.