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Where they come from

Dysomma fuscoventralis is a deepwater cutthroat eel from the Indo-West Pacific. Think outer continental shelf and upper slope, soft bottoms, dim light, and colder water than reef fish ever see. They spend most of their time buried in mud or fine sand with just the head sticking out, waiting for something edible to pass by.

Setting up their tank

Treat this as a species tank project. Your goal is a quiet, dim, sandy burrow world with rock that's locked down and zero escape routes.

• Footprint and volume: At least a 4 ft tank (75-120 gal) with lots of floor space. Bigger is better for stable temps and oxygen.
• Substrate: 4-6 in of fine, sugar-grain aragonite. No coarse gravel. Add several lengths of PVC (1.5-2x the eel's body diameter) buried at angles as starter burrows.
• Rockwork: Place rock on the bare bottom first, then add sand around it so burrowing cannot topple structures.
• Lid and overflows: Tight, weighted lid. Cover every gap, overflow teeth, and powerhead intake with fine mesh. Eels are escape artists.
• Lighting: Keep it very dim. Red light works for observation at night.
• Temperature: Plan on cool water. A chiller is your friend. Target 18-22 C (64-72 F) unless you have proof the fish came from shallow, warmer water.
• Filtration and oxygen: Oversized skimmer, strong aeration, and vigorous surface agitation. These fish like high O2 and very clean water.
• Flow: Gentle along the bottom. Avoid blasting the sand bed.
• Water parameters: SG 1.024-1.026, pH 8.0-8.3, ammonia/nitrite 0, nitrate preferably under 20 ppm.

What to feed them

Wild diet is small fishes, shrimp, and worms. Most won't take pellets. Start with movement and scent, then wean to frozen.

• Starter foods: Live ghost/grass shrimp, small saltwater crabs, or live blackworms (rinsed well) can trigger a strike.
• Staples to switch to: Silversides, lancefish/sandeels, squid strips, prawn/shrimp, clam, and bits of marine fish. Use tongs and wiggle near the burrow entrance after lights out.
• Feeding rhythm: 2-3 times per week. Offer until the belly looks gently rounded, not stuffed. They regurgitate if overfed or stressed.
• Tricks: Soak food in clam juice or a drop of garlic to get interest. Start with thin strips; increase size as the eel learns the routine.
• Supplements: Rotate foods and add a marine vitamin a couple times a week. Avoid goldfish/feeder minnows (thiaminase and disease). Remove leftovers quickly.

How they behave and who they get along with

Expect a stealth ambush predator that spends 90% of the day buried. They key in on scent and movement, then shoot out, grab, and back into the burrow.

• Temperament: Shy with people, decisive with food. Anything that fits in the mouth is food.
• Tankmates: Safest plan is a species-only setup. If you must try companions, pick large, calm, midwater fish that ignore the eel and cannot be swallowed. No small fish, ornamental shrimp, or crabs.
• Other eels: Mixed results. Provide multiple burrows and line-of-sight breaks if housing more than one. Be ready to separate.

Breeding tips

Not a home-aquarium project. Like other cutthroat eels, they spawn in the ocean and produce leptocephalus larvae that drift for months. There are no verified captive breedings or rearing records.

Common problems to watch for

• Refusing food: Very common early on. Go darker, try live shrimp at night, and reduce traffic. Scent frozen food and gradually replace live.
• Escapes: They climb silicone seams and push lids. Add weight to lids and block every cable gap.
• Mouth and snout abrasions: From ramming glass or coarse substrate. Use fine sand and cover reflective ends/sides for the first weeks.
• Warm-water stress: Fast breathing, restless pacing, and surface gulping. If the fish was collected deep, temperatures in the low 20s C may already be too warm. Use a chiller and boost aeration.
• Barotrauma and capture damage: Deepwater fish often arrive compromised. A long, quiet quarantine and pristine water give the best odds.
• Medication sensitivity: Like other scaleless eels, they can react badly to harsh copper or formalin levels. If treatment is needed, use eel-safe dosages and favor praziquantel or metronidazole under guidance.
• Infections/parasites: Watch for cloudy eyes, reddened mouth, or stringy white feces. Address quickly in QT with targeted meds and big water changes.