Flag-tailed glass perchlet

Where they come from

Flag-tailed glass perchlets (Ambassis miops) are little see-through perchlets from coastal areas - think mangroves, estuaries, and slow, tidal creeks. Theyre used to water that swings between fresh-ish and salty depending on the tide, which is why they do best in a real brackish setup instead of plain freshwater.

The cool part is watching a school of them in brackish water under decent lighting. You can see their bones and guts like tiny living X-rays, and the flaggy tail spots make them stand out more than most glassfish.

Setting up their tank

These are schooling fish. If you keep 2 or 3, they get jumpy and hidey and the bolder one often bullies the rest. In a group, they settle down and act like the fish you actually wanted.

• Tank size: 20 gallons is a workable starting point for a small group, but 30+ gallons makes everything easier (more swimming room, less bickering).
• Group size: 6 minimum, 8-12 looks way better and spreads any chasing out.
• Filtration: moderate flow with good oxygenation. They like clean water, but not a river.
• Cover: they will jump if spooked, especially new arrivals. A lid saves headaches.

For the brackish side of things, I keep them at low-to-mid brackish. You dont need a marine reef situation. A steady specific gravity around 1.005 to 1.010 has been a sweet spot for me, and stability matters more than chasing a perfect number.

Decor-wise, give them open midwater to cruise, plus some structure so the group can relax. Roots, rock piles, and tough brackish-friendly plants (or fake plants) work. If you can do mangrove-style wood and leaf litter looks, they really pop against it.

• Temperature: mid-70s F is fine (around 24-27 C).
• pH: theyre pretty forgiving in brackish, usually 7.5-8.5 ends up happening anyway.
• Substrate: sand is nice if you want a natural estuary vibe, but they dont care much.

What to feed them

Theyre small-mouthed micropredators. In my tanks they ignored flakes at first, then some learned, but youll get the best color and behavior on meaty foods. If youre used to livebearers that vacuum up anything, these guys can feel a bit picky early on.

• Great staples: frozen baby brine shrimp, cyclops, daphnia, finely chopped mysis.
• Live treats: baby brine shrimp, grindal worms, small mosquito larvae (where legal/safe).
• Pellets/flakes: can work if small enough, but dont be surprised if they spit it out at first.

Aim the food into the water column. Theyre midwater pickers, not bottom grazers, and they can lose out if you keep them with fast, aggressive eaters.

How they behave and who they get along with

In a proper group theyre active, a little twitchy, and they do that classic glassfish hover-and-dart thing. Youll see short chasing sprees, especially around feeding time, but it should look like pecking-order stuff, not constant harassment.

Theyre not fin-nippers in my experience, but they will eat very small shrimp and tiny fish fry if it fits. Think of them as peaceful predators.

• Good tankmates: other calm brackish fish that wont outcompete them, like smaller gobies, bumblebee gobies (with compatible salinity), knight gobies (if the tank is big), and some brackish-tolerant livebearers.
• Avoid: big, boisterous feeders (theyll get out-eaten), fin-nippers, and anything that views small fish as snacks.
• Skip: delicate long-finned fish. Not because the perchlets shred fins, but because brackish and active schooling fish can stress them.

Breeding tips

They can spawn in aquariums, but its not the easiest project because the eggs and larvae are tiny and the adults will happily snack. If you just want to see spawning behavior, a well-fed group in a planted/brushed-up tank might surprise you.

• Conditioning: heavy feedings of small live/frozen foods for a couple weeks.
• Spawning setup: a separate tank helps a lot. Add fine-leaved plants, spawning mops, or dense cover for eggs.
• After spawning: pull the adults or move the eggs. Otherwise the spawn usually disappears overnight.

If you try raising fry, youll need very small first foods (infusoria, rotifers, or commercial liquid fry foods) before they can take baby brine shrimp. Its doable, just more like raising tiny egg-layers than livebearers.

Common problems to watch for

Most issues I see with these come from two things: keeping them in freshwater because the store had them that way, and bringing home a stressed, half-starved group and expecting them to bounce back on flakes.

• Shyness, hiding, glass-surfing: usually too small a group, too much traffic, or not enough cover.
• Skinny fish that wont eat: common with new arrivals. Try live/frozen foods and dim the lights the first day or two.
• White spot/ich-like outbreaks: often from salinity swings or stress. Keep the salinity steady and quarantine new fish if you can.
• Mysterious losses after water changes: check your mixing. Big swings in specific gravity or temperature can hit them hard.

If you give them stable brackish water, a real school, and small meaty foods, theyre honestly pretty rewarding. Watching a tight group hover in the current with that little flag tail pattern is one of those niche brackish setups that makes you glad you didnt just do another freshwater community.