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Mastacembelus circumcinctus

Common names: Circled Spiny Eel, Banded Spiny Eel
Family: Mastacembelidae
Origin: Southeast Asia (Thailand, Cambodia, Laos; Mekong basin)

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Natural Habitat

• Slow‑moving rivers, floodplains, canals, and backwaters
• Muddy or sandy substrates
• Dense plant growth, roots, and submerged debris
• Often burrows during daylight hours

This species is benthic and crepuscular/nocturnal, relying heavily on cover and substrate.

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Adult Size

• 30–40 cm (12–16 inches)
• Some individuals may exceed this in spacious aquariums

Despite being sold small, this is not a nano or community eel.

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Temperament & Behavior

• Generally peaceful, but predatory
• Will eat:
  • Small fish
  • Shrimp
  • Snails
• Can be territorial toward other spiny eels, especially in confined spaces

Best kept:

• Singly
• Or in very large systems with visual barriers if mixing eels

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Aquarium Requirements

Tank Size

• Minimum: 75 gallons
• Recommended: 125+ gallons for long‑term care

Water Parameters

• Temperature: 24–28 °C (75–82 °F)
• pH: 6.0–7.5
• Hardness: Soft to moderately hard (3–12 dGH)
• Excellent oxygenation and stable water quality required

Filtration

• Strong biological filtration
• Moderate flow with calmer zones
• Absolutely no sharp intake grates

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Substrate & Aquascape (Critical)

• Fine sand substrate only
  • Gravel can cause skin abrasions and infections
• Driftwood, roots, rocks with caves
• Dense plants (real or artificial)
• Leaf litter beneficial
• Tight‑fitting lid mandatory (escape artist)

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Diet

Carnivorous

Preferred foods

• Live or frozen:
  • Bloodworms
  • Blackworms
  • Earthworms (chopped)
  • Prawn / shrimp
  • Mussel
• Some individuals accept sinking carnivore pellets after acclimation

Newly imported specimens often refuse dry food initially.

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Sexual Dimorphism

• Minimal and unreliable
• Females may be slightly thicker‑bodied when mature
• Sexing is difficult without breeding behavior

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Breeding

• Extremely rare in aquariums
• No documented consistent captive breeding method
• Most specimens in the trade are wild‑caught

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Tankmates

 Suitable Tankmates:

• Larger peaceful fish:
  • Severums
  • Silver dollars
  • Peaceful large barbs
  • Larger loaches
• Non‑aggressive cichlids of suitable size

 Avoid:

• Small fish
• Shrimp/crustaceans
• Fin‑nipping species
• Aggressive cichlids
• Sharp‑scaled or hyper‑active fish

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Health & Care Notes

• Scaleless → sensitive to medications
  • Use reduced dosages
  • Avoid copper whenever possible
• Susceptible to:
  • Skin infections
  • Parasites after import
• Quarantine strongly recommended
• Stress shows as refusal to eat or excessive hiding