Williaminae glass fish
Parachela williaminae
Williaminae glass fish exhibit a transparent body with elongated, laterally compressed shapes and distinctive, shimmering silver markings.
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About the Williaminae glass fish
Parachela williaminae is one of those sleek, silvery river "glass fish" types from the Mekong/Chao Phraya systems - built for current and open-water cruising. It is not a tiny rasbora-style fish at all (it can hit around 12 cm/4.7 in), so think "active river minnow" and plan space and flow accordingly.
Also known as
Quick Facts
Size
12 cm SL
Temperament
Peaceful
Difficulty
Advanced
Min Tank Size
55 gallons
Lifespan
5-8 years
Origin
Southeast Asia
Diet
Omnivore leaning carnivore - small insects, zooplankton, frozen foods, quality pellets
Water Parameters
24-28°C
6.5-7.5
2-12 dGH
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Calculate heater sizeCare Notes
- They are jumpy and will launch through tiny gaps, so use a tight lid and keep the water line a bit low. Give them a long tank with open swimming room plus a wall of plants or wood to retreat into.
- Keep them in a real group (8-12+), otherwise they go pale and hide all day. In a big shoal they stay out and you actually see that cool glassy body.
- They do best in soft, clean freshwater with stable temps - think roughly 74-79F, pH about 6.0-7.0, and low nitrate. They do not forgive swings, so do smaller, frequent water changes instead of big random ones.
- Feed like they are tiny predators: live or frozen stuff (baby brine, daphnia, cyclops, small bloodworms) is the fast track to keeping weight on them. If you use dry food, go micro pellets and feed small amounts 2-3 times a day so the shy ones get some.
- Tankmates: small, calm schooling fish and gentle bottom fish are fine (rasboras, small tetras, otos, small loaches). Avoid fin nippers and anything that competes like crazy at feeding time, and skip big gouramis/cichlids that will stress them out.
- They can look healthy right up until they are not, so watch for hollow bellies and clamped fins - that usually means they are being outcompeted or carrying internal worms. Quarantine and deworm if you see weight loss even while they are eating.
- If you want to try breeding, condition them with heavy live food and give fine-leaved plants or spawning mops. Pull the adults after spawning or move the eggs, because they will snack on their own eggs and fry.
Compatibility
Good Tankmates
- Small, chill schooling fish like ember tetras, glowlight tetras, or small rasboras - they match the vibe and nobody bothers the Williaminae glass fish
- Other gentle midwater shoalers like harlequin rasboras or lambchop rasboras - calm, predictable swimmers that do not turn the tank into a chase scene
- Peaceful bottom crews like corydoras (pygmy or regular) - they stick to the floor and keep things social without getting in the glass fish's face
- Otocinclus - super mellow algae grazers, great in planted setups, and they do not compete or hassle them
- Small, non-territorial loaches like kuhli loaches - they are mostly night noodles and won’t stress a shy, see-through midwater fish
Avoid
- Anything nippy like tiger barbs or serpae tetras - the glass fish are peaceful and will get stressed and ragged if fins start getting sampled
- Semi-aggressive territory fish like most cichlids (even the 'not too bad' ones) - they can turn it into constant pressure and the glass fish stop acting normal
- Big mouthy predators like larger gouramis, oscars, or big catfish - if it fits, it gets tested, and these glass fish are slim and easy to gulp
Where they come from
Parachela williaminae (Williaminae glass fish) is one of those little Southeast Asian forest-stream fish that makes you squint the first time you see it. They come from clear, flowing waters with lots of plants and leaf litter, and they tend to show up in the trade as delicate, skinny-looking juveniles.
The big takeaway from their origin: they are built for clean, oxygen-rich water and they do not love sudden changes.
Setting up their tank
If you try to run these like generic community fish in a brand-new tank, you will have a rough time. I have had the best results in a mature tank that has been running a while, with stable parameters and lots of micro-life.
- Tank size: I would start at 20 gallons long for a group. Bigger is easier because it buffers mistakes.
- Group size: 8-12+. They are a schooling fish, and small groups stay jumpy and hide.
- Filtration: strong biological filtration plus gentle-to-moderate flow. Think stream, not washing machine.
- Oxygen: high. Surface agitation helps a lot, especially if you keep them warmer.
- Plants: yes. Give them cover (stem plants, floating plants) and broken sight lines.
- Substrate/decor: dark substrate, wood, leaf litter (if you know how to manage it). They color up and settle down with a darker scape.
- Lighting: moderate. Too bright and they spend the day looking nervous. Floaters are your friend.
I like to seed their tank with seasoned sponge filters or media from an established tank. They react badly to that "new tank wobble" even if your test kit says things look fine.
They jump. Use a tight lid, cover filter gaps, and do not leave open feeding doors. I have lost more than one glass fish to a tiny opening I thought was "probably fine."
Water-wise, aim for clean and steady. Soft to moderately hard can work depending on your local water, but stability beats chasing a perfect number. Keep nitrate low, keep the water clear, and do smaller, regular water changes instead of big swings.
What to feed them
They are micropredators. If you only offer big flakes and pellets, some will learn, but a lot of them just slowly waste away. The fish looks "not sick" right up until it suddenly is.
- Best staples: live or frozen baby brine shrimp, cyclops, daphnia, small bloodworms (sparingly), chopped blackworms.
- Good training foods: high-quality micro pellets, crushed flakes, small granules (feed tiny portions).
- Feeding rhythm: 2-3 small feeds a day at first, then 1-2 once they are putting on weight.
- Target feeding: use a pipette or turkey baster to put food right into the school. It cuts down on food getting stolen by faster tankmates.
New imports often ignore dry food for a while. I start with frozen cyclops or baby brine, then mix in micro pellets once they are eating aggressively.
How they behave and who they get along with
They are peaceful, but they are not "tough." A confident, boisterous community will keep them pinned in a corner, and then you will see the classic combo of stress plus weight loss.
- Temperament: shy to moderately active once settled. They school loosely and hang midwater.
- Best tankmates: small, calm fish that will not outcompete them (tiny rasboras, pencilfish, small peaceful danios in the right setup), and gentle bottom fish (small Corydoras, kuhli loaches).
- Avoid: fin nippers, big gouramis/cichlids, hyperactive feeders, anything that sees tiny fish as snacks.
- Shrimp: adults may be okay with larger shrimp, but expect baby shrimp to disappear.
If your glass fish stay pale and stick to the glass or corners, usually something is off: too bright, too little cover, too much traffic from tankmates, or water that is not as stable as it seems.
Breeding tips
Breeding is possible, but it is not a "they spawned in the community tank and I raised 50 fry" kind of fish for most people. They scatter eggs, and the adults (and basically everything else) will eat them.
- Conditioning: heavy feeding of live/frozen small foods for a couple of weeks.
- Setup: a separate tank works best. Use fine-leaved plants or spawning mops, and gentle aeration.
- Egg protection: marbles or a mesh-bottom insert helps the eggs fall out of reach.
- After spawning: pull the adults. Keep the tank dim.
If you try breeding in a brand-new bare tank, the eggs/fry tend to lose to water quality swings and fungus. A small, mature sponge-filtered setup is your best friend.
Common problems to watch for
Most issues I have seen with Williaminae glass fish come down to stress, shipping damage, and slow starvation. They do not always show obvious symptoms until they are already in trouble.
- Slow weight loss: usually not enough of the right food, or tankmates are beating them to it.
- Sudden deaths after a water change: big parameter swings, temperature mismatch, or too much cleaning at once.
- Clamped fins and hiding: bright light, lack of cover, not enough of a group, or aggressive tankmates.
- White spots (ich) and other parasites: common on new arrivals. Quarantine if you can, and raise temperature only if you also raise oxygen.
- Mouth/gill issues and rapid breathing: often tied to low oxygen, dirty water, or gill parasites. Increase aeration and check ammonia/nitrite first.
Do not buy them if they are already pinched-bellied and hovering at the surface in the store. Some can be recovered, but a lot of those fish never bounce back, even in a great setup.
If you keep them in a calm, planted, mature tank and you feed small meaty foods consistently, they stop being "advanced" pretty fast. The hard part is getting them through that first month and into a steady routine.
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