Three-spined stickleback

1) Where they come from

Three-spined sticklebacks are little tough-guys from coastal areas across the Northern Hemisphere. You’ll find them in everything from cool freshwater streams to brackish ditches and tidal creeks—places where conditions swing around a lot. That “built for chaos” background is a big reason they’re such interesting aquarium fish.

2) Setting up their tank

Give them more footprint than height. A 20 long works nicely for a small group, and bigger is always easier because it spreads out the drama (and they can be dramatic).

For brackish, I’ve had the best luck around low-end brackish—think slightly salty, not “mini reef.” Aim for a steady salinity instead of chasing numbers daily. Mix your saltwater in a bucket first, then add it to the tank. Don’t sprinkle salt into the aquarium.

• Tank size: 20 long for a group; 10g can work for a single fish or a pair short-term, but it gets tense fast
• Temp: cool to moderate (they don’t love tropical heat). Low-to-mid 60s°F is great; low 70s can work if oxygen is high
• Flow/oxygen: they appreciate clean, well-oxygenated water—use a decent filter and consider an airstone
• Substrate: sand or fine gravel; they pick and peck constantly
• Hardscape: piles of small rocks, driftwood, and plant thickets to break line-of-sight
• Plants: hardy options that tolerate brackish (java fern, anubias, some crypts depending on your salinity), plus algae growth is a bonus

Lids matter. Sticklebacks can launch when startled, especially during sparring or breeding mode. I’ve lost one to a tiny gap that I swore was “too small to matter.”

3) What to feed them

These are hunters. They’ll take prepared foods, but you’ll get better color, better body shape, and way more natural behavior if you lean into frozen/live foods.

• Staples I rotate: frozen bloodworms, daphnia, brine shrimp, mysis
• Live treats: blackworms, mosquito larvae (if you can collect safely), live brine shrimp
• Prepared foods: small sinking carnivore pellets or high-protein micro pellets (introduce slowly and mix with frozen at first)

Feed small amounts 1–2 times a day. If you dump a big meal in, the bold fish eats everything and the shy one fades away. I like to spread the food across the tank so everyone gets a shot.

4) Behavior and tankmates

Sticklebacks are curious, clever, and—depending on the individual—kind of pushy. You’ll see them posture, flare, and chase. A calm tank with lots of cover keeps it interesting instead of stressful.

A group can work, but the social dynamics shift fast once a male decides it’s breeding season. If you want the classic stickleback behavior (nest building and courtship), you’ll also see the classic stickleback attitude.

• Best kept: species-only, especially if you want to see breeding behavior
• If you try tankmates: choose fast, non-nippy fish that can handle brackish and cooler water (and be ready with a backup plan)
• Avoid: slow fish, long fins, shrimp you care about, and tiny fish that fit in a stickleback’s mouth

5) Breeding tips (the fun part)

Breeding sticklebacks are honestly one of the coolest “small fish” projects you can do. The male builds a nest (usually in plants) and guards it hard. He’ll court the female, herd her to the nest, and then fan the eggs to keep water moving over them.

• Conditioning: lots of frozen/live foods for a couple weeks
• Set the stage: dense plants/algae, fine material (like short plant fibers), and calm corners
• Watch the male: brighter colors and nonstop patrolling usually means he’s ready
• After spawning: consider removing the female (and sometimes other fish) so the male can guard without constant battles

Once the fry are free-swimming, the male may still guard them for a bit, but eventually they become “just food” if the tank is crowded or he’s stressed. A separate grow-out tank makes life simpler.

6) Common problems to watch for

Most stickleback problems I’ve seen come down to three things: warm stagnant water, poor diet variety, and bullying. They’re hardy, but they don’t forgive “lazy setups” the way some livebearers do.

• Fin damage from aggression: usually starts as ragged fins and stress hiding—add cover, rearrange decor, or separate fish
• Low oxygen/high temp stress: hanging near the surface, fast breathing—cool the tank, increase surface agitation, clean the filter
• Parasites from wild foods/fish: flashing, skinny fish, stringy poop—quarantine new arrivals and be cautious with live foods from unknown sources
• Salinity swings: odd behavior after water changes—pre-mix brackish water and match temperature/salinity before adding

If you keep the water cool, the tank well-oxygenated, and you manage the social drama, they’re ridiculously rewarding. You’ll actually catch yourself just watching them “think,” which isn’t something I say about every fish.