Armoured stickleback

Where they come from

Armoured sticklebacks (Indostomus paradoxus) come from slow, plant-choked waters in Southeast Asia - think quiet backwaters, marshy edges, and little ditches with tons of leaf litter. They are one of those fish that look like a tiny pipefish got shrunk and put into freshwater.

That background explains basically everything about them in the aquarium: they like calm water, lots of cover, and food that drifts past their face.

Setting up their tank

If you treat these like regular nano fish, you'll be frustrated. They do best in a species tank or with extremely gentle tankmates, and the tank has to be set up for hunting micro-food all day.

• Tank size: 10+ gallons is comfortable for a small group. You can do smaller, but stability and food density get harder fast.
• Filtration: sponge filter or a baffled filter with very low flow. They hate being blasted around.
• Substrate: sand or fine gravel. I like adding leaf litter (catappa/oak/beech) so microfauna builds up.
• Hardscape: lots of stems, moss, and twiggy stuff. They use plants like a jungle gym and as ambush points.
• Lighting: not too intense unless you have floating plants. Dim tanks make them bolder.
• Cover: floating plants and dense corners matter more than open swimming space.

Water-wise, they are not super picky, but they are sensitive to instability. I kept mine in neutral to slightly acidic freshwater with moderate hardness and they were fine. What they do not like is sudden swings, big temperature jumps, or a tank that gets dirty and then gets "fixed" with a huge water change.

What to feed them

This is the make-or-break part. Indostomus are micropredators. Most will ignore flakes and pellets like they do not exist, especially at first. They want tiny live foods that move.

• Staples that worked for me: live baby brine shrimp (newly hatched), live daphnia/moina, grindal worms, microworms.
• Great "lazy day" food: frozen cyclops, frozen daphnia, finely shaved frozen mysis (only for bigger adults), frozen baby brine shrimp if they recognize it.
• Nice bonus: copepods and seed shrimp populations in the tank (leaf litter and moss help a lot).

They hunt by sitting still and snapping at passing prey. I had the best results feeding small amounts 2-3 times a day rather than one big dump. If you only feed once, the bold individuals eat and the shy ones slowly fade.

How they behave and who they get along with

They are calm, slow, and kind of sneaky. Most of the time they perch in plants and watch. You will see little bursts of movement when they hunt or posture at each other.

Males can be a bit territorial, but it is more "get out of my plant" than real damage, especially if the tank is planted thick. In a sparse tank they get stressed and you see more chasing.

• Best setup: species-only group, heavily planted, lots of sight breaks.
• If you must do tankmates: tiny, calm fish that will not outcompete them (and that is a short list).
• Avoid: anything fast, anything nippy, and basically any fish that will hoover up live foods before the Indostomus even notices.

Breeding tips

Breeding is doable, but it is not a quick win. You need well-fed adults, calm conditions, and lots of fine plants. They are bubble-nest-ish in behavior, with the male tending eggs in a small shelter.

• Give males places to claim: small caves, bits of tubing, dense moss clumps, leaf stacks.
• Condition with live foods for a couple weeks. Baby brine shrimp and small daphnia make a huge difference.
• Keep the tank peaceful and the flow gentle so the male can guard without getting stressed.

If you get fry, the first-food problem is even more intense than with the adults. You will need infusoria-type foods and copepods early on, then baby brine shrimp once they are big enough.

Common problems to watch for

• Slow starvation: belly starts to look pinched, they perch more and hunt less. Fix by increasing live micro-food frequency and reducing competition.
• New tank syndrome: they look fine, then you lose one at a time. These fish do better in mature, stable tanks.
• Stress from flow: constantly getting pushed around, hiding nonstop, not taking food. Swap to a sponge filter or baffle the output.
• Internal parasites: wild fish sometimes come in thin even if they eat. Quarantine and consider a deworming plan if weight does not improve.
• Over-cleaning: big water changes and scrubbing can crash the microfauna they rely on and can swing parameters. Do smaller, more frequent changes instead.