Peacock Eel Care Guide: Tank Setup, Feeding & Compatibility for Macrognathus siamensis

Species Overview#

The peacock eel (Macrognathus siamensis) is a slender, scaleless spiny eel from the rivers of Southeast Asia. Despite the common name, it is not a true eel — it belongs to the family Mastacembelidae, a group of freshwater oddballs prized for their snake-like movement, expressive eyes, and a row of ocelli (eyespots) running along the dorsal fin. Hobbyists keep them for the same reason they keep black ghost knifefish: they bring a distinctly different silhouette to a community tank, and they reward keepers patient enough to learn their nocturnal rhythms.

Peacock eels are not difficult once their basic needs are met, but they punish keepers who shortcut the setup. The two requirements that matter most — fine sand substrate and a sealed lid — are decided before you ever bring the fish home. Get those right and the rest of the care is straightforward.

Adult size

10-12 in (25-30 cm)

Lifespan

8-18 years

Min tank

35 gallons

Temperament

Peaceful, predatory on small fish

Difficulty

Intermediate

Diet

Carnivore

Natural Habitat & Origin#

Peacock eels come from slow-moving, heavily vegetated rivers and floodplains across Thailand, Cambodia, Vietnam, and parts of India. The water is warm, soft, and slightly acidic, with leaf litter and silty bottoms that give them somewhere to burrow during the day. In the wild they spend daylight hours buried with only their snout visible, then emerge after dark to hunt small invertebrates and insect larvae. Replicating that day/night rhythm in the home aquarium is the key to actually seeing the fish behave naturally instead of cowering.

Appearance & Identifying Markings#

The peacock eel earns its name from the row of three to six dark ocelli — round black eyespots ringed in pale gold — that run along the rear half of the dorsal fin. The body is yellow-tan to olive brown, often with faint horizontal lines and a paler belly. The snout is elongated into a soft, fleshy proboscis the eel uses to sift sand for food.

Two related species are routinely mislabeled as peacock eels at fish stores. The fire eel (Mastacembelus erythrotaenia) is much larger (up to 36 inches) and has bright red lateral striping. The zigzag eel (Mastacembelus armatus) reaches 24+ inches and has a chain-link pattern instead of distinct eyespots. If the fish you are buying tops 14 inches in the tank or carries red coloration, it is not a peacock eel.

Size & Lifespan#

Peacock eels reach 10-12 inches in captivity, with 15 inches reported in older specimens given large tanks and steady feeding. Growth is slow — expect a 4 inch juvenile to take 18-24 months to hit 8 inches. Lifespan in well-kept aquariums runs 8-18 years, which puts them in the same long-term-commitment bracket as goldfish or large cichlids.

Water Parameters & Tank Requirements#

Peacock eels tolerate a useful range of water conditions, but they are sensitive to ammonia and to sharp swings in temperature or pH. Cycle the tank fully before introducing one — they are too expensive and too long-lived to risk on an unstable system.

Ideal Water Parameters#

The numbers below cover the species' wild range and the conditions reported by experienced keepers. Aim for the middle of each range and prioritize stability over chasing exact figures.

Tank Size & Substrate#

A 35-gallon tank is the practical minimum for a single adult peacock eel, and 55+ gallons is better if you want to keep tank mates or a second eel. Footprint matters more than height — peacock eels live on the bottom, so a long, shallow tank like a 40 breeder or 55-gallon serves them better than a tall hex.

For aquarium dimensions and footprint planning, prioritize length over depth — a 48-inch-long tank gives an adult eel room to stretch out and pick a hiding spot away from tank mates.

Filtration, Flow & Escape-Proofing#

Run a canister filter or a robust hang-on-back rated for at least 1.5x the tank volume. Peacock eels are heavy feeders on protein-rich foods, which means more waste and more nitrate buildup than a typical community tank produces. Cap any intake strainer with a coarse sponge pre-filter — eels will investigate intakes and can wedge themselves into uncovered slots.

Keep flow moderate. Peacock eels evolved in slow-moving water and dislike strong currents whipping across the substrate. Aim a powerhead at the surface for gas exchange rather than blasting it across the sand bed.

Diet & Feeding#

Peacock eels are obligate carnivores that hunt by smell after dark. They will not race to the surface for flakes, and most refuse dry pellets indefinitely. Plan to feed live or frozen meaty foods.

What Peacock Eels Eat#

A varied carnivore rotation keeps them in good condition:

• Frozen bloodworms — the easiest staple, accepted by nearly all specimens
• Frozen or live blackworms — high-fat treat, excellent for conditioning thin or newly imported fish
• Frozen brine shrimp and mysis — useful variety; less filling than worms
• Small earthworms — chopped to size; outstanding nutrition for adults
• Ghost shrimp or feeder guppies — occasionally, but quarantine first to avoid parasite introduction

Skip beef heart and mammalian meats. The fat profile is wrong for tropical fish and fouls water fast.

Feeding Techniques for Picky Eaters#

Feed at night with the room lights off — turn the tank light off 30 minutes before feeding to cue the eel out of its burrow. Use long feeding tongs or a turkey baster to deliver food directly in front of the eel's snout. If you simply drop food into the tank, faster tank mates will eat it before the eel finds it.

A newly imported peacock eel may refuse food for 1-2 weeks while it acclimates. Resist the urge to keep adding food — uneaten worms decay fast in warm water. Try blackworms or live ghost shrimp to break a hunger strike. Once the eel takes food consistently, transition toward frozen options to reduce parasite risk.

Feed adults 3-4 times per week. Juveniles can take small meals daily. Stop when the belly looks gently rounded — a pencil-thin profile means underfed; a balloon belly means overfed.

Tank Mates & Compatibility#

Peacock eels are peaceful toward fish too large to swallow and ruthless toward fish that fit in their mouths. Plan the stocking list around that single rule.

Compatible Community Fish#

Mid-to-large peaceful species work well. Good candidates include:

• Gouramis (pearl, blue, opaline)
• Larger tetras (Congo, Buenos Aires, lemon)
• Rainbowfish (Boesemani, turquoise)
• Peaceful cichlids (angelfish, severums, larger acaras)
• Mid-sized loaches (yoyo, skunk)
• Larger plecos that can hold their own at the substrate

A Senegal bichir is one of the better large-tank pairings — both species are nocturnal substrate dwellers, both are tolerant of one another, and they fill different vertical zones in a deep tank.

Species to Avoid#

Also avoid fin-nipping species like serpae tetras and tiger barbs (the eel's exposed dorsal is tempting), and aggressive bottom-dwellers like territorial cichlids (red devils, jaguars) that will compete for the same hiding spots.

Multiple Eels#

Peacock eels generally tolerate conspecifics in tanks of 75 gallons or larger with plenty of caves and hiding territory. Introduce both at the same time so neither has established a burrow as its own. In smaller tanks, expect the dominant eel to harass the other off feeding territory.

Tank Décor & Hiding Spots#

A bare tank is a stressful tank for this species. Build the layout around hiding cover and indirect light.

Plants & Caves#

Dense planting along the back and sides gives the eel cover during the day. Java fern, anubias (epiphytes that do not need substrate roots), Vallisneria, and Cryptocoryne all work and tolerate the warm temperature range. Add hardscape hides — sections of PVC pipe sized just larger than the eel's diameter, hollow driftwood, or stacked slate caves. Multiple hiding options matter, because an eel that cannot find a comfortable burrow will pace the front glass for hours and refuse food.

Lighting#

Run lighting low to moderate. Bright reef-grade light increases stress and pushes the eel into permanent hiding. If you keep light-demanding plants, use floating species (frogbit, salvinia) or tall stems to break up the surface and shade the bottom.

Common Health Issues#

Peacock eels are tough once settled, but their scaleless skin makes them more vulnerable to skin parasites and to standard medications than typical scaled fish.

Ich & Skin Flukes#

Ich (Ichthyophthirius multifiliis) shows up as white grains of salt on the body and fins. Treat with elevated temperature (82-84°F for two weeks) plus a half-dose of an ich medication labeled for scaleless fish. Avoid full-strength malachite green — peacock eels can react badly. Aquarium salt can be used at half the typical dose (around 1 teaspoon per 5 gallons), but never the full freshwater rate.

Skin flukes (gyrodactylus) cause mucus build-up, scratching against decor (flashing), and clamped fins. Praziquantel is the standard treatment and is generally safe for scaleless species at label dose.

Copper Sensitivity & Medication Warnings#

Avoid copper-based medications entirely. Copper, formalin at full strength, and organophosphate dewormers can kill peacock eels. Read every medication label for "do not use with scaleless fish" warnings and dose at half-strength when in doubt. When treating, remove activated carbon and run an airstone for extra oxygenation — medicated water holds less oxygen.

Nutritional Deficiencies & Refusal to Eat#

Refusal to eat is the most common husbandry problem. Causes include stress from a new environment, water quality issues, ammonia exposure, daytime feeding attempts (the eel is not active), and wrong food choices (dry pellets). Test water first, switch to live blackworms or ghost shrimp to restart the feeding response, and feed at night. A peacock eel that refuses food for more than three weeks despite good water and the right diet is in serious trouble — examine for visible disease and consider a vet consultation.

Where to Buy & What to Look For#

Peacock eels turn up regularly in the freshwater fish section of mid-sized local fish stores, usually as 4-7 inch juveniles. Quality varies widely, so inspect carefully.

Selecting a Healthy Specimen at Your Local Fish Store#

Typical Price Range#

Expect $8-$20 for a captive-raised or wild-imported juvenile in the 4-7 inch range. Larger sub-adults run $25-$40. Premium specimens with vivid coloration sometimes hit higher. Prices below $8 usually mean stressed or freshly imported stock — wait for the next shipment to settle in store.

Acclimation#

Drip-acclimate over 60-90 minutes. Peacock eels handle the standard float-and-mix method, but their scaleless skin makes them more sensitive to pH and temperature shock than scaled species. Use a slow drip (one drop per second) into a bucket, then net the eel directly into your tank — never pour bag water into your display.

Turn the tank lights off for the first 24 hours after introduction. Do not feed for the first 2-3 days. The eel will likely vanish into the substrate immediately; resist the urge to dig or rearrange to find it. It is acclimating, not dying.

Quick Reference#

• Tank size: 35 gallons minimum for a single adult; 55+ for groups or community
• Temperature: 73-82°F (76-79°F is the sweet spot)
• pH: 6.5-7.5
• Hardness: 5-15 dGH
• Substrate: Fine sand, 2+ inches deep — non-negotiable
• Diet: Carnivore — frozen bloodworms, blackworms, brine shrimp, occasional earthworms
• Tank mates: Gouramis, larger tetras, rainbowfish, peaceful cichlids, Senegal bichir
• Avoid: Dwarf shrimp, nano fish, fin-nippers, aggressive bottom-dwellers
• Lid: Tight-fitting with all openings sealed
• Difficulty: Intermediate
• Lifespan: 8-18 years