Slender brotula

Where they come from

Slender brotulas are deep-slope fishes from the Indo-Pacific, living way down on the continental edges. Think hundreds to more than a thousand meters deep, cold, dark, and quiet. They spend their time hugging the bottom, nosing around soft sediment and rock crevices for little crustaceans and worms.

Setting up their tank

Plan for a cold, low-light, low-traffic setup. They are shy, mostly nocturnal, and hate bright light. A species-only tank is best.

• Tank size: 200-300 liters minimum for a single adult. Long footprint beats tall.
• Temperature: 4-10 C (39-50 F). Keep it rock steady with a reliable chiller and a controller.
• Salinity: 33-35 ppt. pH around 8.0-8.3.
• Oxygen: Keep it high. Strong aeration and surface agitation are your friends.
• Lighting: Very dim. Use red spectrum for viewing if you must. They relax in darkness.
• Flow: Gentle near the bottom with decent overall turnover. Avoid blasting their burrow zones.
• Substrate: Fine sand mixed with silt if you can manage it. Skip sharp crushed coral.
• Hides: Build a maze of PVC tubes and stable rock caves. Make it tight, dark, and secure.

Filtration-wise, think oversized skimmer, big biomedia, and low-nutrient but not sterile water. They put out a fair bit of protein once eating. Intakes should be guarded so they do not get sucked in during night forays.

What to feed them

Getting a new brotula to eat is the whole game. They key in on scent and movement, not bright light. Start after lights-out, and deliver food right to the cave entrance with long tongs.

• Starter foods: live blackworms (rinsed in saltwater), live mysids, small live shrimp if you can source cold-tolerant ones.
• Transition foods: finely cut raw shrimp, clam strips, squid slivers, small silverside pieces, PE mysis.
• Prep: soak meaty foods in a vitamin mix and a touch of marine garlic to get interest and cover the freezer smell.
• Routine: small portions 3-4 times a week. Their metabolism at 6-8 C is slow; do not overfeed.
• Technique: wiggle food at the entrance, then lay it just inside and back off. Patience beats chasing.

How they behave and who they get along with

They are cave-huggers. Most of the day is spent half-hidden with just the head showing. At night, they cruise low over the sand. Not outwardly aggressive, but anything bite-sized that blunders by can disappear.

• Best kept solo. Two in the same tank tend to stress each other unless the tank is very large with multiple deep retreats.
• Tankmates, if you must: coldwater, calm species that do not outcompete at feeding time and are too big to be a snack. Avoid flashy, active swimmers that will keep it on edge.
• Not reef safe in the warmwater sense. Corals do not belong in a 6-8 C system anyway, and they will nose through anything soft in search of food.

Breeding tips

I have never seen a confirmed captive spawning of Dicrolene, and I would not plan a project around it. Sexing is not practical without dissection, and deepwater cues (pressure, day-length at depth, seasonal plankton pulses) are hard to mimic. Enjoy it as a display animal if you can keep one eating and stable.

Common problems to watch for

• Refusal to eat: common the first 2-3 weeks. Keep it dark, reduce foot traffic, and try live foods to break the ice.
• Heat creep: anything over 10 C for long stretches speeds up metabolism and crashes them. Size your chiller generously.
• Low oxygen: cold water holds more O2, but deepwater fish still crave high saturation. Add an airstone or increase surface chop.
• Light stress: bright lights lead to frantic dashes and face rubbing at cave entrances. Dim it down.
• Injuries: they wedge hard into crevices. Use smooth PVC and avoid sharp rock edges.
• Medication sensitivity: be cautious with copper and formalin in very cold water. I run observational quarantine and targeted treatments only.
• Decompression damage from capture: gas issues, poor equilibrium, or rapid decline on arrival. If it shows up like this, outcomes are usually poor regardless of care.