Sunda viviparous brotula

Where they come from

Sunda viviparous brotulas (Ungusurculus sundaensis) are little secretive marine cusk-eels from the Sunda region in Southeast Asia. Think murky rubble, crevices, and tight hiding spots where you mostly see a head poking out at dusk. They are not a "display fish" in the usual sense - they are more like a cool predator you get to know over time.

Setting up their tank

Give them a tank that looks like a rock pile fell into it on purpose. They want caves, slots, and narrow gaps they can wedge into. The more secure they feel, the more you will see them.

• Tank size: I would not do less than 30 gallons for a single adult, and 50+ if you want options for tankmates or more than one brotula.
• Rockwork: lots of small caves and tight cracks. I like stacking rock on PVC "feet" so it is stable and leaves undercuts.
• Substrate: sand is fine, but the real key is structure. Rubble zones and shell/rock bits help them feel at home.
• Flow: moderate. You do not need a high-energy SPS-style blast, but do not let detritus build up in their lairs.
• Lighting: keep it on the dim side or provide shaded areas. They get bolder with lower light and a consistent day/night schedule.

Filtration and stability matter a lot because these are messy, meaty-food fish. A solid skimmer, good mechanical filtration you actually clean, and regular water changes will save you headaches. They do not forgive "old tank funk" the way some hardy fish do.

• Temperature: aim for typical reef temps (around mid-70s F) and keep swings small.
• Salinity: keep it steady at reef strength (around 1.025). They react badly to sloppy top-off habits.
• Nitrate/phosphate: they can live with some nutrients, but high and rising numbers usually show up as poor appetite and skin issues later.

What to feed them

These are predators. Mine ignored flakes and pellets completely. Once they recognize you as the food source, they get surprisingly bold at feeding time.

• Best staples: frozen/thawed shrimp, mysis, chopped clam, chopped squid, chunks of marine fish (sparingly).
• Live foods: sometimes helpful for new imports (small ghost shrimp or live mysis), but I try to convert to frozen fast.
• How to feed: use feeding tongs or a turkey baster and place food near their cave entrance at lights-out.
• Schedule: small meals 3-4 times a week works well. Daily heavy feeding just trashes water and makes them lazy.

How they behave and who they get along with

Brotulas are mostly nocturnal and very hole-oriented. They claim a home and defend that immediate area. You will see short bursts of speed, then back into the crack like nothing happened.

• Temperament: not a community fish. Not constantly aggressive, but anything that fits in their mouth is on the menu.
• Tankmates that usually work: larger, calm fish that do not harass caves (some tangs, larger wrasses that sleep in the sand, rabbitfish).
• Tankmates to avoid: small gobies/blennies, tiny wrasses, ornamental shrimp, small crabs, and anything that likes the same caves (dottybacks can be a disaster).
• Inverts: snails are usually fine. Shrimp are a gamble at best - I would assume they will eventually get eaten.

If you try more than one, expect drama unless the tank is big and the rockwork has multiple separated cave systems. Even then, you may end up with one dominant fish and one that never comes out.

Breeding tips

They are livebearers (that is the "viviparous" part), which is wild for a marine fish. In home tanks, breeding is possible but not something I would plan a setup around unless you already keep oddballs and you like a challenge.

• Pairing: you need a compatible male/female, and sexing is not straightforward without experience and close observation.
• Conditioning: heavy, varied meaty feeding and stable water for months is what seems to get them in the mood.
• Birthing: if it happens, you may never see it. The young are small and disappear into rockwork fast.
• Raising fry: expect to need a separate rearing setup and tiny live foods. Most people lose them in the display to filtration or tankmates.

Common problems to watch for

Most problems with this species come from three things: shipping stress, starvation (they hide and never learn to eat), and water quality getting away from you because of heavy foods.

• Not eating: very common in new arrivals. They may only feed after lights-out for a while.
• Skin damage: scrapes from rough rock or getting pinned in a too-tight hole. Usually looks worse than it is, but can get infected in dirty water.
• Marine ich/velvet: possible like any marine fish, and these guys do not handle harsh treatment well if they are already stressed.
• Jumping/escaping: often happens the first week or two, or after a night-time scare.

If your brotula is always out in the open, breathing hard, or wandering like it cannot find a home, something is off (usually oxygen, water quality, or harassment). These fish should look calm and "anchored" to a chosen spot most of the time.