Forktail blue-eye (Forktail rainbowfish)

1) Where they come from

Forktail blue-eyes (Pseudomugil furcatus) come from Papua New Guinea, hanging around slow creeks and swampy edges where plants and roots break up the flow. That “dappled light over plants” vibe is basically their comfort zone in a tank.

2) Setting up their tank

Think of these as “small fish that like room.” A longer tank beats a tall one because they spend their day cruising midwater and flashing at each other.

• Tank size: 15–20 gallons is a comfy starting point for a proper group (they look best in numbers)
• Temp: ~24–27°C / 75–81°F
• pH: roughly neutral to slightly alkaline (around 7.0–8.0 is usually fine)
• Hardness: moderate is your friend; they generally don’t love super-soft, super-acid water long-term
• Flow: gentle to moderate; enough to keep the water fresh but not blasting them around

Decor-wise, I’ve had the best luck with a planted setup: fine-leaf plants, some floating cover, and open lanes for swimming. Dark substrate makes their colors pop, and a background (even just black vinyl) helps them feel less exposed.

3) What to feed them

Their mouths are tiny. They’ll take dry food, but you’ll get way better color and energy if you mix in small frozen/live foods. In my tanks, the difference between “surviving” and “constantly displaying” was basically diet.

• Staple: high-quality micro pellets or crushed flake (small enough that they don’t spit it out)
• Frozen: baby brine shrimp, daphnia, cyclops, finely chopped mysis (if it fits), rotifers
• Live (if you can): baby brine shrimp, microworms, grindal worms, small daphnia

4) Behavior and tankmates

Forktails are peaceful and surprisingly bold once settled. Males do that “look at me” fin-flicking and short chase displays, but it’s more pageant than fight. If you only keep a couple, they can get shy or pick on the weakest fish. A real group spreads everything out.

• Best group size: 8–12+ if you’ve got the space
• Nice ratio: more females than males (or at least not all males)
• They school loosely—more like a busy little cloud than a tight formation

Tankmates should be calm and not mouthy. Anything that’s fast, nippy, or big enough to see them as snacks will keep them stressed and washed out.

• Good matches: small rasboras, ember tetras, peaceful barbs (the tiny calm ones), otocinclus, small Corydoras, Amano shrimp (usually), nerite snails
• Use caution: big/boisterous tetras, most danios in small tanks (too much chaos), dwarf cichlids if they’re territorial
• Skip: fin nippers, aggressive community fish, anything that can fit them in its mouth

5) Breeding tips

They’re egg scatterers and they’ll spawn pretty regularly if they’re happy—often without you noticing. The trick is keeping the eggs/fry from becoming “live food” for the adults and the rest of the tank.

• Give them a spawning spot: a yarn mop or fine-leaf plants (java moss, guppy grass, etc.)
• Condition them with baby brine/daphnia and good micro foods
• Collect eggs by moving the mop to a small hatching container every few days
• Gentle air stone + clean water in the hatching container helps a lot

If you don’t want a whole breeding project, you can still get the occasional survivor in a heavily planted tank. Floating plants + moss + lots of tiny hiding spots is your best bet.

6) Common problems to watch for

Most issues I’ve seen with forktails come down to three things: unstable water, being kept in too-small groups, or being fed food that’s too big/too dry-only.

• Shyness/pale colors: usually not enough of a group, too much bright light with no cover, or aggressive tankmates
• Wasting away: food particles too large, not enough variety, or competition at feeding time
• Sudden losses after adding them: tank not mature, ammonia/nitrite spikes, or big parameter swings from large water changes
• Fin damage: typically nippy tankmates (less often male sparring in cramped setups)