Singapore glassy perchlet

Where they come from

Singapore glassy perchlets (Ambassis kopsii) are little see-through perchlets from Southeast Asia. You will usually find them around estuaries, mangroves, and slow coastal waterways where fresh and salt mix. That brackish background explains basically every quirk they have in the aquarium.

Setting up their tank

Think of these as small schooling fish that want space to cruise, but also want cover to duck into. A longer tank beats a tall one. I have had the best luck keeping a group in a 20 long or bigger, and they look way more relaxed once the group is 8+.

• Tank size: 20 gallons long minimum for a proper group (bigger is better if you want tankmates)
• Group size: 8-12 is the sweet spot; fewer and they get skittish and nippy
• Filtration: steady, not blasting; they like clean water but not a washing machine current
• Lighting: moderate; they color up and feed better with some shaded areas

For decor, I do a mix of open swimming room and structure. Driftwood, rocks, and clumps of hardy plants (or fake plants) work. In brackish, true plants can be hit or miss, so I lean on things like Java fern and Anubias tied to wood (they often tolerate low-end brackish), plus algae-coated rocks and floating cover.

Use marine salt mix, not table salt. Measure with a refractometer if you can. Hydrometers work, but they are easy to misread in the low brackish range.

What to feed them

They are micro-predators. Mine act like tiny piranhas when food hits the water, but they are picky about texture. If you only offer flakes, you might watch them spit it out all day.

• Best staples: frozen mysis, brine shrimp, daphnia, chopped krill, Cyclops
• Live foods they go nuts for: baby brine shrimp, grindal worms, small mosquito larvae (where legal/safe)
• Dry foods: small pellets and good flakes can work, but train them onto it slowly

I feed small amounts 1-2 times a day. They do better with frequent little meals than one big dump, especially if you have a mixed tank where faster fish steal everything.

How they behave and who they get along with

They are schooling, midwater fish with a mild predator vibe. In a good-sized group they are confident and stay out in the open. In a small group they get nervous, hide, and sometimes start pecking each other.

They are not the best choice with tiny shrimp or tiny fry. If it fits in their mouth, they will try. With fish, they usually do fine with other brackish species that are not pushovers and not small enough to be snacks.

• Good tankmates: bumblebee gobies, knight gobies (in larger tanks), mollies in similar salinity, figure 8 puffers only with caution (often too nippy), larger peaceful scats/monos only if the tank is big enough and salinity matches
• Avoid: long-finned slow fish, very small fish (they may hunt), aggressive brackish predators, freshwater community fish that do not like salt
• Best look: species-only or a calm brackish community with lots of midwater room

Breeding tips

Breeding is possible, but it is not as straightforward as livebearers or many egg scatterers. They spawn in groups, and the eggs and fry are easy snacks for the adults. If you want to try, plan around separating eggs or raising fry elsewhere.

• Conditioning: heavy feed with live/frozen foods for a couple weeks
• Spawning setup: fine-leaved cover (Java moss-style texture, spawning mops, or dense artificial grass) plus gentle filtration
• What to do next: pull adults after you see spawning behavior, or remove the mop/cover with eggs to a small rearing tank
• First foods: rotifers/infusoria, then baby brine shrimp once fry can take it

Common problems to watch for

Most issues I see with A. kopsii come from two things: being kept too fresh for too long, and being underfed or kept in small groups. Once those are fixed, they are pretty hardy.

• White spot/ich outbreaks after purchase: common if they were stressed in transit; treat in a hospital tank and keep salinity stable
• Wasting away: often they are not getting enough food in a competitive tank or they never accepted dry food
• Fin damage: usually nipping from small groups or cramped tanks
• Sudden losses after water changes: usually SG or temperature swings, or using the wrong salt

If you buy a new group, quarantine them if you can. They come in stressed pretty often, and once one fish in the school breaks with ich, the whole tank can follow. A calm quarantine with stable brackish water and good food saves a lot of headaches.