Phenax brotula

Where they come from

Phenax brotula (often called Brotula phenax in the trade) is a deepwater brotula - one of those eel-ish, cave-dwelling marine fishes that spends its life wedged into rockwork. They show up from the western Atlantic/Caribbean region, usually associated with reefs but down in darker, cooler, deeper zones compared to the usual reef fish you see at shops.

That background explains basically everything about keeping them: they like it dim, they like tight cover, and they do not appreciate being forced into bright, busy reef conditions.

Setting up their tank

Think of the tank like a burrow system with water around it. If you set up a pretty aquascape with a few decorative caves, your brotula will still try to live behind the rocks, under the rocks, or in the overflow.

• Tank size: I would not try one in anything under 55 gallons, and bigger is better if you plan tankmates. They are not marathon swimmers, but they need stable water and lots of territory choices.
• Rockwork: build multiple deep caves and dead-end tunnels. Use epoxy/putty and make it collapse-proof. They push and wedge themselves in hard.
• Substrate: sand is fine. They do not need deep sand, but they do appreciate a softer bottom for cruising at night.
• Lighting: keep it moderate to low, or at least provide shaded zones. If your tank is a bright SPS spotlight, expect a very secretive fish.
• Flow: moderate. They like oxygenated water but do not want to get blasted out of their hideouts.

I also recommend planning for how you will feed it. You want at least one hide with a clear "front porch" area so you can drop food right where it lives, instead of hoping it finds scraps after the tangs and wrasses are done.

What to feed them

They are meaty-food predators. Mine did best once it learned that a feeding stick meant dinner and it did not have to compete in the open.

• Best staples: thawed shrimp, squid, clam, scallop, and chunks of marine fish (not freshwater feeder stuff).
• Good add-ons: enriched mysis, krill (as a treat, not every meal), and quality frozen "carnivore" blends.
• How often: small meals 3-4 times a week beats huge feedings. They can get fatty if you overdo it.
• How to deliver: long tweezers or a feeding stick, placed near the same cave entrance each time.

One thing I would skip is live feeder shrimp/fish as a habit. It can work for getting a new import started, but it trains them to hunt the clean-up crew and it is an easy way to introduce parasites.

How they behave and who they get along with

Most of the time you will see a face in a hole and a tail tucked behind rock. At night they do slow patrols and ambush anything that fits in their mouth. They are not "mean" in the way triggers can be, but they are absolutely predatory.

• Good tankmates: medium, calm fish that will not pick at it or steal every bite (bigger gobies, tangs, angels that are not bullies, larger cardinals).
• Avoid: tiny fish, shrimp, crabs, and small snails you care about. Also avoid hyper food thieves like some wrasses if your brotula is shy.
• With other brotulas: possible in a big tank with lots of rock and multiple caves, but expect territorial behavior. I would not attempt pairs unless you can separate if things go sideways.

Breeding tips

Breeding Phenax brotula in home aquariums is basically "nice if it happens" territory. Sexing is not straightforward, and getting a compatible pair is the hard part. That said, brotulas (the broader group) are known for shelter-focused spawning, often in caves.

• If you ever try: run a species tank or very quiet fish-only system so the pair feels secure.
• Provide: multiple deep caves with narrow entrances and calm zones where they can post up.
• Conditioning: heavy, varied meaty foods for months, not weeks.
• Do not count on raising larvae: if they produce pelagic larvae (common in many marine fishes), you are looking at a separate larval system and live foods like rotifers and copepods from day one.

Common problems to watch for

This is an expert fish mostly because of the combo of shipping stress, secretive habits, and the fact that you can miss problems until they are advanced. You have to be the kind of keeper who notices little changes: a cave that used to have a face in it, feeding response, breathing rate.

• Refusing food after purchase: very common. Give it cover, reduce light, and offer tempting foods (clam on the half shell, shrimp chunks) on tongs at night.
• Getting outcompeted: you will think it is eating because food disappears, but it is the other fish. Target feed and watch it actually swallow.
• Parasites (ich/velvet): deepwater, stressed imports can crash fast. Quarantine is your friend, but set QT up with PVC caves so it feels secure enough to eat.
• Injuries from rockwork: scraped skin and damaged fins happen if they wedge into sharp rubble. Smooth the inside of caves where you can and avoid jagged rubble piles.
• Mysterious vanishings: usually the overflow/sump, or it has buried itself deep in the rock. Always check mechanical filter socks and pump chambers.