Three-spot righteye flounder

Where they come from

The three-spot righteye flounder (Samariscus triocellatus) is a small coastal flatfish from the western Pacific. Think shallow sandy areas, rubble patches, and seagrass edges where it can vanish into the bottom in a second. Those three eye-like spots are not just for looks - they help break up the outline when the fish is half-buried.

Setting up their tank

If you have not kept flatfish before, the big mindset shift is that floor space matters more than height. You want a wide footprint and a calm, stable system. I would not try one in a brand-new tank.

• Tank size: I would start at 30-40 gallons for a single fish, bigger if you want tankmates. A long tank beats a tall one every time.
• Substrate: fine sand, not crushed coral. Grain should be small enough that they can bury without scraping themselves up.
• Sand depth: 2-3 inches is usually plenty. Give them room to cover the body, not just sit on top.
• Rockwork: keep it stable and leave open sandy lanes. They like an edge where sand meets rock.
• Flow: moderate and not blasting the bottom. Aim for turnover in the tank, but avoid a sandstorm.
• Filtration: oversized and consistent. These fish eat meaty foods and the tank will feel it if you slack on export.
• Lighting: not picky, but provide shaded areas. They spend a lot of time partially buried and do not love being in a spotlight all day.

A tight lid is worth doing even if you think a flounder will not jump. They can launch when spooked, especially during acclimation and the first week or two.

What to feed them

These guys are ambush predators. If it fits in the mouth, it is food. In captivity, the goal is getting them onto frozen and keeping the diet varied so they do not slowly waste away on one type of shrimp.

• Best staples: frozen mysis, chopped shrimp, chopped clam, squid strips, and quality marine carnivore blends.
• Treats (use sparingly): live ghost shrimp, live mollies acclimated to salt, small live crabs. Live can help start stubborn new imports.
• Avoid: freshwater feeders like goldfish/rosies (fatty acid issues), and relying only on brine shrimp (too little nutrition unless enriched).
• Feeding method: tongs or a feeding stick works great. Place food right in front of the face on the sand.
• Schedule: small meals daily at first. Once settled, 4-5 feedings per week usually keeps body condition nice.

Watch the body shape. A healthy flounder looks filled out behind the head and along the back edge. If it starts looking thin even though it is "eating," it may not be getting enough nutrition or it may have internal parasites.

How they behave and who they get along with

Most of the time you will see a pair of eyes and a little outline in the sand. Then feeding time happens and suddenly it is lightning fast. They are not aggressive in the "chase you around" way, but they are absolutely predatory.

• Good tankmates: calm fish that stay midwater and are too large to swallow (bigger gobies, some wrasses, cardinals, larger clownfish in a big enough setup).
• Bad tankmates: anything shrimp-sized (shrimp, small gobies, tiny blennies), and fish that pick at the bottom.
• Also avoid: boisterous feeders that will steal every bite before the flounder can line up a strike.
• Inverts: snails are usually fine; small crabs may become food; decorative shrimp are basically expensive snacks.

They can handle other sand-sitters if there is plenty of space, but I would not mix it with aggressive burrow defenders (some dottybacks, territorial damsels, or a nasty watchman goby in a small tank). The flounder needs to feel relaxed enough to feed consistently.

Breeding tips

Breeding this species in home aquariums is basically a long shot. Flatfish often have pelagic eggs and tiny larvae that need specialized live foods and very stable rearing setups. I have never seen a reliable hobby track record for Samariscus triocellatus specifically.

Common problems to watch for

Most issues with righteye flounders come down to shipping stress, rough substrate, and not getting them eating well enough early on.

• Refusing food: common in the first days. Keep the tank calm, offer live to start if needed, and do not let tankmates outcompete it.
• Abrasions and belly sores: almost always from coarse substrate or being forced onto rock. Fix the sand first, then treat infections if they pop up.
• Crypt/velvet: they can get the usual marine parasites. Quarantine is your friend, but be careful with meds and oxygen levels.
• Internal parasites: if it eats but keeps losing weight or spits food a lot, consider deworming protocols in a QT after you have it stable and feeding.
• Nitrate creep and dirty sand: meaty feeding plus a sand bed can turn into a nutrient sink. Siphon lightly and keep up with water changes.
• Starvation by competition: they can be "invisible" at feeding time. Target feed so you know it is getting its share.

Last thing: acclimation matters. Take your time with salinity and temperature, keep lights low, and give it a quiet sandy spot right away. The first two weeks set the tone for whether it becomes a long-term pet or a "mystery disappearance" under the sand.