Comb flounder

Where they come from

Comb flounders like Marleyella bicolorata are Indo-Pacific sand-sitters. You find them on shallow sandy or rubble bottoms where they disappear in plain sight, waiting for small fish and shrimp to wander too close.

That background matters because they are not a "reef perch" kind of fish. They want a bottom they can work with, and they do a lot better when you set the tank up around that.

Setting up their tank

Plan the tank from the bottom up. This fish lives on the sand, not in the rockwork, so your substrate choice is basically your life support system for it.

• Tank size: I would not bother under 75 gallons, and 100+ is better. They spook easily and need floor space more than height.
• Substrate: fine sand, 1-2 inches. Avoid sharp crushed coral. They bury and scoot, and rough stuff beats up the belly and fins.
• Rockwork: keep it stable and set rocks on the glass, then add sand around. A flounder can undermine rocks without trying.
• Flow: moderate. Give them a calmer zone on the bottom so they are not sandblasted all day.
• Filtration: strong, because they are messy carnivores and uneaten meaty food goes foul fast.
• Lighting: they do not need intense lighting, but they do need a normal day-night rhythm. Too bright with no shade can keep them stressed.

Cover every gap on the lid. They can launch when startled, especially during the first couple weeks. I have seen "bottom fish" end up on the floor because someone opened a cabinet door too hard.

What to feed them

This is where most people lose them. They often arrive thin, stressed, and picky. Once they are eating well they are pretty hardy, but getting there can take patience.

• Best starter foods: live blackworms (if you can do them safely), live ghost shrimp, small live mollies/guppies acclimated to marine (use caution), or live mysis if available.
• Frozen once settled: mysis, chopped shrimp, chopped clam, scallop, squid, and quality marine carnivore blends.
• Avoid: feeder goldfish/rosies (bad fat profile), big chunks they can choke on, and anything that fouls the water if ignored.

I like to target feed with long tweezers or a feeding stick right in front of the face. They hunt by ambush, so they do not always "find" food that drifts around the tank like a tang would.

Feeding schedule: small meals more often beats one big dump. Juveniles do well with daily feedings. Adults I usually feed 3-5 times a week, watching body thickness behind the head and along the back.

How they behave and who they get along with

They are calm, sneaky, and surprisingly bold once settled. Most of the time you will see eyes and an outline in the sand, then a sudden "snap" when something edible passes by.

The rule for tankmates is simple: if it fits in their mouth, it is food. And they can take bigger bites than you think.

• Good tankmates: medium to large, non-bullying fish that ignore the bottom (bigger tangs, rabbitfish, some angels with caution), and sturdy fish that will not pester them.
• Avoid: small gobies, blennies, firefish, small wrasses, tiny cardinals, small shrimp, and basically any "nano" fish you want to keep long-term.
• Also avoid: aggressive feeders that will steal every bite (large wrasses, dottybacks, overly pushy damsels). They will outcompete a flounder fast.
• Inverts: snails and larger hermits are usually fine. Cleaner shrimp are a coin flip - I would assume they will eventually get eaten, especially at night.

They do best in a quieter tank where you are not constantly rearranging rock or blasting the sandbed. Once they pick a favorite area, they tend to stick to it.

Breeding tips

Breeding Marleyella bicolorata in home aquariums is basically a long shot. Like many marine flatfish, they are pelagic spawners and the larvae are not "tiny versions of the adults" - they go through a drifting stage and then a crazy metamorphosis where the eyes migrate.

If you ever keep a pair long-term and see dusk spawning behavior (rising into the water column together), your best bet is to treat it like other pelagic spawners: separate larval rearing tank, gentle round flow, and a serious live food pipeline (rotifers, copepods, then Artemia). Most hobbyists never get past the first few days.

Common problems to watch for

Most problems trace back to three things: shipping stress, starvation, and injuries from rough substrate or unstable rockwork.

• Not eating: common after import. Try live foods, dim the lights for a few days, and reduce competition at feeding time.
• Thin body or pinched look behind the head: they are burning reserves. Increase feeding frequency and use higher-calorie foods like chopped shrimp and clam once they will take them.
• Scrapes/ulcers on the belly side: usually from coarse substrate, rough rubble, or being pinned against rock. Switch to finer sand and check flow patterns.
• Parasites (marine ich/velvet): flatfish can show heavy breathing and hiding before you see spots. Quarantine is hard with sand-sitters, but it is still worth doing.
• Ammonia spikes: caused by uneaten meaty food or a young biofilter. They do not handle bad water well when already stressed.

If you see rapid breathing, failure to bury, or they are constantly perched awkwardly against the glass, take it as a sign something is off. In my experience it is usually water quality, too much flow at the bottom, or harassment from tankmates.