Dwarf Neon Rainbowfish

Where they come from (and why they look so good)

Dwarf Neon Rainbowfish (Melanotaenia praecox) come from New Guinea—mostly clear, flowing streams and lake edges where the water stays warm and there’s a lot of plant growth along the margins.

That “neon” blue body with the red fins isn’t just for show—these fish are built for bright light, clean water, and constant motion. If you give them that vibe at home, they color up fast.

Setting up their tank

These are small fish, but they’re active like little torpedoes. I wouldn’t keep a group in anything smaller than a 20 gallon long, and a 29+ is even nicer if you want them really relaxed and displaying.

• Tank size: 20 gallon long minimum for a proper group
• Temp: 24–27°C / 75–81°F
• pH: around 6.5–7.5 works great (they’re pretty flexible)
• Hardness: moderate is fine; avoid extremes
• Flow/filtration: moderate filtration with good oxygenation (they appreciate clean, moving water)

Layout-wise, I like a “racetrack” in the middle: plants and hardscape pushed to the sides/back, open swimming space across the front. They’ll spend all day flashing color and chasing each other through the open lane.

A tight lid helps. They’re not the worst jumpers, but excited rainbowfish do rainbowfish things—especially at feeding time or if something startles them.

What to feed them

They’re easy to feed, but they look their best when you give them variety. Mine always colored up more with a mix of quality dry food and a couple frozen/live options each week.

• Staple: a good small pellet or flake (look for higher protein, not “wheat first”)
• Color/conditioning: frozen daphnia, baby brine shrimp, cyclops
• Treats: live baby brine shrimp, microworms (great if you ever try raising fry)
• Greens: they’ll pick at some veggie-based foods, but they’re not algae-eaters

I feed small amounts 1–2 times a day. They’re enthusiastic eaters, so it’s easy to overdo it—especially in smaller tanks where leftover food turns into cloudy water fast.

Behavior and tankmates

These guys are peaceful, busy, and constantly interacting. Males will spar and “flare” those red fins, but it’s more posturing than damage—assuming they’ve got space and a decent-sized group.

• Great tankmates: small peaceful tetras, rasboras, Corydoras, Otocinclus, small plecos, peaceful loaches
• Also good: shrimp (adults usually fine; tiny shrimp babies may disappear)
• Avoid: fin-nippers (some barbs), aggressive cichlids, anything big enough to view them as snacks

Breeding tips (if you feel like going down the rabbit hole)

They’re egg scatterers, and they’ll spawn pretty readily once they’re settled. The trick isn’t getting eggs—it’s keeping the adults from treating the eggs like snacks.

• Use a spawning mop (yarn) or fine-leaf plants like java moss
• Condition with frozen/live foods for a week or two
• Pull the mop every day or two and move it to a small rearing tank/container with gentle aeration
• Eggs usually hatch in about a week depending on temperature
• First foods: infusoria/rotifers, then baby brine shrimp once they can take it

Common problems to watch for

Most issues I’ve seen with praecox come down to stress from cramped quarters, small groups, or water that’s slipping because the tank is overstocked.

• Faded color / clamped fins: often stress, too few fish, or not enough swimming room
• Ich and other parasites: they can show spots quickly after a new fish addition—quarantine helps a lot
• Fin nips: usually from poor tankmate choices or too small a group
• “Mysterious” losses: often a new tank that isn’t stable yet, or chronic ammonia/nitrite issues

One more thing: buy the best batch you can. Some stores get skinny, stressed imports. Look for fish with full bodies, clear eyes, fins held open, and that “always moving” rainbowfish attitude. Healthy praecox settle in fast and are ridiculously rewarding.