Unknown (name appears invalid for a fish)

Where they come from

Quick heads-up: I cannot find a real marine fish that matches the name Quassiremus polyzona. It might be a misspelling, an old trade name, or something that got mangled in a list somewhere.

That said, the care questions people ask under names like this usually end up being about an eel-like reef predator (often a moray, snake eel, or worm eel) that shows up as a rare import. If that is what you have, the advice below is the kind of stuff that keeps these oddballs alive long-term.

Setting up their tank

Treat this like setting up for a secretive, escape-prone ambush predator that wants a bolt-hole and low stress. A lot of the failures with mystery eels are not water chemistry, its the tank being too open, too bright, or too easy to slip out of.

• Tank size: I would not bother under 40-55 gallons for most eel-like marine oddballs, and bigger is easier if it gets past 18-20 inches.
• Lid: Tight. No gaps around plumbing, cords, or overflows. If a pencil fits, an eel can fit.
• Hiding spots: PVC elbows, rock caves, and a couple deep crevices. Give it at least two choices so it can relocate without feeling exposed.
• Substrate: If it buries, use fine sand and keep sharp rubble out. If it does not bury, sand still helps with comfort and reduces reflected light.
• Flow and filtration: Moderate flow, strong biological filtration, and a skimmer that can handle messy meals.
• Lighting: Dimmer zones matter. Even in reef tanks, build shaded areas with overhangs.

For parameters, keep things boring-stable: normal reef salinity (around 1.025), steady temperature (mid-70s F), and low nitrate. The bigger issue is oxygen and cleanliness after feedings. These fish can be hardy, but a dirty tank catches up with them fast.

What to feed them

Assume it is a carnivore that hunts by smell. New imports often ignore food for a bit, then suddenly switch on once they feel safe. The trick is offering the right foods in the right way, without polluting the tank.

• Best starters: fresh or frozen/thawed shrimp, squid, scallop, clam, and marine fish flesh (not oily freshwater stuff).
• Avoid: feeder fish, goldfish, and anything freshwater-based long term. It is a nutrition mess and can introduce problems.
• Feeding method: long tongs or a feeding stick. Hold the food near its cave entrance and let it grab, then stop. Do not wave it around like a toy.
• Frequency: juveniles 2-3 times a week, larger individuals often 1-2 solid meals a week. Overfeeding is the fastest way to wreck water quality.
• Vitamins: soak in a marine vitamin once or twice a week if it will take it.

How they behave and who they get along with

Most of these eel-shaped mystery predators are not mean in the "chase you around" way. They are mean in the "anything that fits in my mouth disappears" way. They also get bolder after dark, so what looks peaceful at noon can be a different story at 2 a.m.

• Good tankmates: larger, sturdy fish that do not sleep on the sand and are not bite-sized.
• Risky tankmates: gobies, blennies, small wrasses, tiny clowns, cardinals, and anything that wedges into the same caves.
• Inverts: shrimp and small crabs are usually snacks. Big cleaner shrimp sometimes last, sometimes do not. Urchins and snails are often fine, but expect "bulldozer" moments.
• Corals: usually ignored, but the fish can topple frags while it cruises.

Breeding tips

In home aquariums, breeding is basically a lottery for most eel-like marine predators, especially if you cannot confidently sex them. Some species spawn pelagic larvae that are extremely hard to raise. The best you can do is keep one well-fed and stress-free and watch for pairing behavior if you ever keep a confirmed male and female.

Common problems to watch for

Most issues come down to shipping damage, starvation (they look fine until they do not), and tanks that are not secured. Keep a close eye during the first 4-6 weeks.

• Refusing food: often stress or too much light/traffic. Add more cover, feed at night, and do not keep changing foods every day.
• Rapid breathing or hanging at the surface: low oxygen or ammonia after a messy feeding. Increase aeration and clean up uneaten food fast.
• Skin issues: scrapes from sharp rock, especially if it wedges into tight holes. Smooth the caves and give wider PVC options.
• Ich and velvet: eels and scaleless fish can be touchy with meds. Quarantine is your friend, and copper can be risky depending on the actual species.
• Escapes: the #1 killer. Check the lid weekly and after any maintenance.