Fire eel

1) Where they come from

Fire eels (Mastacembelus erythrotaenia) come out of Southeast Asia, mostly slow rivers and floodplain areas around Thailand/Cambodia/Vietnam. Think warm water, lots of leaf litter, roots, muddy/sandy bottoms, and plenty of places to disappear. That “vanish into the scenery” lifestyle explains about 80% of their tank needs.

2) Setting up their tank

This is an advanced fish mostly because it gets big, it’s strong, and it’s a professional escape artist. A cute 10-inch juvenile turns into a thick, powerful eel that wants floor space more than height.

• Tank size: I’d treat 125 gallons as a starting point for an adult, with a long footprint (6-foot tank is your friend). Bigger is honestly easier.
• Substrate: fine sand is the best. They dig and “bury” themselves; gravel can scratch them up.
• Hardscape: driftwood, root tangles, PVC tubes hidden behind décor, and caves they can fully fit into.
• Plants: optional, but tough plants (Java fern, Anubias) tied to wood work better than delicate rooted stuff—fire eels rearrange the furniture.
• Flow/filtration: moderate flow with beefy filtration. They’re messy eaters and big-bodied fish = big waste.
• Temp/pH: warm tropical range; keep it stable more than chasing a magic number.

Lighting doesn’t need to be bright. If you want to actually see your fish, floating plants or dimmer LEDs help a lot. Mine became way more confident with shaded areas and cover.

3) What to feed them

Fire eels are predators with a great sense of smell. They learn routines fast, and once they trust you, they’ll take food from tongs like a puppy. The challenge is getting a new one eating and not overdoing fatty foods long-term.

• Go-to foods: earthworms/nightcrawlers (cut to size), shrimp, mussel, clam, squid pieces, quality frozen carnivore mixes.
• Good variety: bloodworms for smaller juveniles, blackworms if you can get them clean, silversides/white fish occasionally.
• Pellets: some will learn sinking carnivore pellets, but many need “real” food first.
• Feeding schedule: juveniles more often; adults usually do great with a few solid meals per week.

4) Behavior and tankmates

Most of the time they’re calm, a little shy, and kind of goofy once they settle in. But they’re still predatory. If it fits in their mouth, it’s a menu item. Also: they’re surprisingly strong and can bulldoze décor if it’s not stable.

• Good tankmates: larger, sturdy fish that won’t pick at them—big barbs, larger rainbowfish, sturdy cichlids (not the hyper-aggressive kind), larger peaceful catfish.
• Avoid: small tetras, guppies, small loaches, juvenile anything you’re attached to.
• Also avoid: fin-nippers and bullies (some barbs/cichlids can be a problem), because fire eels don’t handle constant harassment well.

They’re also a hands-off fish. They’ll recognize you, they’ll come out for food, and they can be interactive—but they don’t want to be handled. Netting one is a whole event, and they can get scraped up if you’re rough about it.

5) Breeding tips

Breeding fire eels in home aquariums is rare. Most of what you see in the trade is wild-caught or from large-scale setups. Sexing them isn’t straightforward, and getting a compatible pair plus the right seasonal triggers is the real hurdle.

6) Common problems to watch for

Most issues I’ve seen come down to three things: scratches/infections from rough substrate or décor, stress from poor hiding spots or aggressive tankmates, and water quality sliding because the fish is big and eats meaty foods.

• Escapes: the #1 “problem.” Seal the lid and every gap.
• Nose/skin abrasions: often from gravel, sharp rocks, or squeezing into tight décor. Sand + smooth hides help a lot.
• Refusing food: common in new arrivals. Dim lights, offer worms, don’t crowd them, and give them time.
• Parasites and skinny-new-eel syndrome: wild-caught individuals can come in rough. Quarantine if you can.
• Ich/skin infections: scaleless-ish fish tend to react strongly to meds. Go slow with dosing and watch them closely.
• Bloat/constipation: too much rich food or big chunks too often. Mix in worms and smaller portions.