Rubenstein's nannocharax

Where they come from

Rubenstein's nannocharax is one of those small African oddballs that gets under your skin. They come from Central/West African river systems where the water is often soft, a little acidic, and moving. Think leaf litter, sand, roots, and that tea-stained look from tannins in a lot of spots.

That background explains 90% of their vibe in the aquarium: they like stability, clean water, and they act way more relaxed when you give them cover and gentle flow.

Setting up their tank

These are not a "toss them in a community tank" fish. They settle in slowly, and they show their best behavior and color in a calm, established setup. I have had the best luck starting them in a tank that has been running a while, with lots of biofilm and zero swings.

• Tank size: 20 gallons long works well for a small group. Bigger is easier to keep steady.
• Group size: 8-12 if you can. They act tighter and less twitchy in numbers.
• Substrate: fine sand or smooth small gravel. They spend a lot of time low in the tank.
• Decor: wood, root tangles, rounded stones, leaf litter, and plants around the edges for cover.
• Flow: gentle to moderate. They appreciate movement but do not want to get blasted around.
• Lighting: subdued. Floating plants or tannins help a lot with confidence.

Water-wise, I treat them like a "soft, clean, stable" fish. Soft to moderately soft water is where they look and behave best. Keep nitrates low and do not let the tank get dirty, but also do not go crazy scrubbing everything spotless every week.

What to feed them

Most of the ones I have kept were not enthusiastic pellet eaters at first. Once settled, some will take small quality micro pellets, but live and frozen foods are what really get them going.

• Frozen: cyclops, daphnia, baby brine shrimp, finely chopped bloodworms (not as an everyday staple).
• Live: baby brine shrimp, grindal worms, microworms, small daphnia if you can culture it.
• Dry: micro pellets and fine flakes, but introduce slowly and mix with frozen at first.

If you are quarantining them (and you should), watch that they are actually eating. A fish that looks "fine" but ignores food for days is usually stressed, bullied, or dealing with internal issues.

How they behave and who they get along with

They are peaceful, but they are not pushovers. In a group they do little sparring displays, and you will see a loose pecking order. It is usually more posturing than damage, but cramped tanks can turn that into fin nips.

They are also easily outcompeted at feeding time. Fast midwater fish will steal everything unless you plan around it.

• Good tankmates: small, calm tetras, African butterflyfish only in large setups (and if the nannocharax are too big to be snacks), peaceful dwarf cichlids that stay low drama, small catfish like Corydoras in similar water (though true soft-water Cory species fit better).
• Use caution: boisterous barbs, danios, bigger gouramis, or anything that rushes food.
• Avoid: fin nippers, aggressive cichlids, and any predator that sees a 1-2 inch fish as a bite-size meal.

Breeding tips

Breeding Nannocharax rubensteini is doable, but it is not a "free fry" fish. Adults will snack on eggs and tiny fry, and they seem pickier about conditions than a lot of small egg scatterers.

• Set up a separate breeding tank if you can. 10-20 gallons, mature sponge filter, dim light.
• Use soft, slightly acidic water and keep it very clean. Gentle aeration helps.
• Add spawning media: clumps of fine-leaf plants, moss, or a spawning mop.
• Condition heavily with live and frozen foods for a couple of weeks.
• If you see chasing and tight pairing behavior, check the plants/mop for eggs.

Fry are tiny. The first foods need to be equally tiny. Infusoria, rotifers, or commercial liquid fry foods can bridge the gap until they can take baby brine shrimp.

Common problems to watch for

Most issues I have seen with this species come down to stress: too much light, too much activity in the tank, unstable water, or being kept in pairs instead of a real group.

• Not eating in a new tank: usually stress. Add cover, dim the lights, offer live foods, and stop fussing in the tank.
• Fin nipping within the group: often crowding or not enough line-of-sight breaks. Add more wood/plants and keep a bigger group.
• Wasting away despite eating: consider internal parasites. Quarantine and treat thoughtfully, and do not mix meds "just because."
• Ich and other common diseases: they can get it like any small fish, but they hate rapid temp/pH swings during treatment.

If you give them a mature tank, a group, calm tankmates, and a steady feeding routine, they reward you with really cool behavior. They are one of those fish that makes you slow down and actually watch the tank.