Johnston's Docimodus

Where they come from

Docimodus johnstoni is one of those African cichlids that shows up in the hobby mostly because hardcore Tanganyika people want something different. Theyre from Lake Tanganyika, and they come with that whole lake vibe: hard, mineral-rich water, lots of rock structure, and fish that dont do well with sloppy setups.

Setting up their tank

Give them space and give them rockwork. I wouldnt even consider this species in a small tank. Theyre not a tiny shellie you can tuck into a 20 long. Think big footprint first, then build upward with rocks.

• Tank size: I like 75g absolute minimum, and 125g feels way more forgiving if you plan on tankmates.
• Footprint matters more than height. Long tanks make territory lines easier.
• Rock piles with caves and cracks. Build it stable (zip ties, epoxy, or egg crate under the rocks) because big cichlids will redecorate.
• Substrate: sand or fine gravel. Sand makes them act more natural and is easier on mouths and gills.
• Filtration: oversized and boring-reliable. Strong bio capacity plus decent flow.
• Water: hard and alkaline. Keep it consistent rather than chasing numbers.

I also keep lighting moderate. Too bright and a lot of Tanganyikans stay edgy. Plants are usually a non-issue because most setups are rock and sand, but if you try any, stick to tough stuff and expect it to get dug up.

What to feed them

This is an expert fish partly because feeding is easy to get wrong long-term. You want variety, but you also want to avoid dumping rich foods every day and watching the fish get fat, bloaty, and lazy.

• Staple: quality cichlid pellets that arent ultra-high fat.
• Frozen foods: mysis, krill, chopped shrimp, and occasional high-protein treats in small amounts.
• Add some roughage: spirulina-based foods or veggie-leaning pellets a few times a week.
• Feeding rhythm: smaller meals more often beats one big dump.

How they behave and who they get along with

Expect a territorial Tanganyika cichlid with attitude. Theyre not mindless killers, but theyre not community fish either. If you keep them with timid species, the timid fish will spend their life hiding and slowly wasting away.

Ive had the best luck keeping them with other Lake Tanganyika fish that can handle themselves and that use different zones of the tank. Rockwork helps a ton. Break up sight lines and you break up a lot of the drama.

• Good direction for tankmates: robust Tanganyikan cichlids of similar size and temperament, especially those that hold different territories.
• Avoid: slow, gentle fish and anything small enough to be bullied relentlessly.
• Stocking approach: either a focused species tank, or a carefully planned Tanganyika mix in a large tank with heavy rockwork.

Breeding tips

Breeding is doable, but its not a beginner project. The first challenge is getting a compatible pair without one fish turning the other into a punching bag. If you want to try, start with a small group of juveniles in a big tank and let a pair form naturally.

• Start with juveniles and grow them out together. Watch for a pair that sticks to the same area without constant violence.
• Give them multiple caves and a couple of flat rock surfaces. Fish choose the spot, not you.
• Once a pair forms, be ready to remove extra fish if the dominant one starts pinning others in corners.
• If you get fry, have a plan. A lot of Tanganyika setups are not fry-friendly unless you add piles of small rock rubble for hiding.

Common problems to watch for

Most issues I see with this kind of fish come from three things: unstable water, bad diet habits, and social stress. The fish might look okay for a month, then slowly fall apart.

• Chronic hiding, clamped fins, faded color: usually stress from tankmates or not enough cover.
• Mouth injuries and torn fins: territory fights, especially in smaller tanks or sparse rockwork.
• Bloat-like symptoms: overfeeding, too many rich foods, or a stressed fish not digesting well.
• Hole-in-the-head style pitting: often tied to long-term water quality issues and poor diet variety.