Bigeye brotula
Glyptophidium longipes
The Bigeye brotula features a long, slender body with prominent, large eyes and a mottled brown coloration that aids in camouflage on the ocean floor.
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About the Bigeye brotula
Glyptophidium longipes is a deepwater cusk-eel (brotula) from the western Indian Ocean - a slender, eel-ish fish with oversized eyes and long ventral-fin rays. It is a bathyal slope species from a few hundred meters down, so its real-world needs (cold, dark, high-pressure habitat) make it essentially an observation-only "research" animal rather than a practical aquarium fish.
Also known as
Quick Facts
Size
26 cm
Temperament
Peaceful
Difficulty
Expert
Min Tank Size
500 gallons
Lifespan
unknown
Origin
Western Indian Ocean (East Africa to South Africa)
Diet
Carnivore - small fishes and invertebrates (presumed for deepwater ophidiids)
Water Parameters
4-10°C
7.8-8.4
8-12 dGH
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This species needs 4-10°C in a 500 gallon tank. Use our heater calculator to find the right wattage.
Calculate heater sizeCare Notes
- Give it a dim tank with lots of tight caves and overhangs (PVC elbows work great); they hate being on display and will stress-sulk in open rockscapes.
- Keep it cool for a marine fish: aim around 68-72F, stable salinity 1.024-1.026, and don't let nitrate creep up (try to stay under ~10-15 ppm) or they go off food.
- Feed after lights-out with tongs - small meaty stuff like enriched mysis, chopped shrimp, clam, and squid; start with frozen, but you may need a few live ghost shrimp to get a new one eating.
- They are ambush predators, so anything that fits in their mouth will vanish - don't pair with tiny gobies, small wrasses, or ornamental shrimp you care about.
- Best tankmates are calm, non-nippy fish that won't harass a shy cave fish; avoid triggers, puffers, big dottybacks, and any wrasse that loves picking at fins.
- Watch for shipping/collection damage and parasites - these deepwater types often come in beat up; quarantine in low light and keep oxygen high with strong surface agitation.
- If it starts hanging out in the open during the day, take it as a stress flag: check for bullying, too much flow blasting its cave, or water getting warm.
- Breeding in home tanks is basically a long shot; if you ever see two tolerating the same cave, count it as a win and don't expect babies without a dedicated species setup.
Compatibility
Good Tankmates
- Peaceful midwater planktivores like anthias or chromis - they mind their own business and wont hassle a shy brotula that hangs near caves
- Calm reef-safe wrasses (think fairy and flasher wrasses) - active but not mean, and they do not compete much for the brotulas hiding spots
- Small, non-predatory gobies and blennies (clown gobies, tailspot blennies, similar) - generally chill neighbors as long as there are plenty of holes and perches
- Cardinalfish (Banggai, pajama, etc.) - slow, peaceful, and they do fine with a nocturnal cave fish that comes out more at feeding time
- Dwarf angels with decent manners (coral beauty type) - usually ok if the tank is roomy and the brotula has a rockwork maze to duck into
- Reef-safe tangs and rabbitfish - bigger but typically not interested in a secretive bottom-cave fish, just avoid crowding the rockwork
Avoid
- Triggers and other pushy, bitey fish - they will bully it out of its cave and can rip at the fins when it tries to settle back in
- Large hawkfish, groupers, and other ambush predators - if it fits in their mouth, it is food, and a brotula hanging near ledges is an easy target
- Big, territorial dottybacks and damsels - constant dive-bombing around the rockwork stresses them out and you will barely see the brotula eat
- Anything super grabby at feeding time like chunky puffers - they outcompete a shy nocturnal feeder and can nip when it comes out after lights out
Where they come from
Bigeye brotulas (Glyptophidium longipes) are deepwater cusk-eels. Think dim, cool, high-pressure habitats where they spend most of their time tucked in tight spots and only really get busy once the lights are low. That deepwater background explains 90% of the headaches people run into with them in home tanks.
If you are used to reef fish that live under bright lights and warm water, this one will feel backwards. Plan around darkness, calm water movement, and cooler temps.
Setting up their tank
This is an expert fish because the tank has to be built around the fish, not the other way around. Mine did best in a species-focused setup: dim lighting, lots of hard cover, and very stable water. They are not a "showpiece in a reef" kind of fish.
- Tank size: I would not bother under 50-75 gallons just for stability and footprint. Bigger is easier to keep steady.
- Lighting: keep it subdued. If your tank has strong reef LEDs, give the brotula a shaded zone that stays dark all day.
- Aquascape: rock piles with deep caves, lots of overhangs, and at least one tight "bolt hole" they can fully disappear into. PVC sections hidden behind rock work great too.
- Substrate: sand is fine, but the main thing is secure caves that will not collapse.
- Flow: moderate overall, but make sure there are calm pockets behind the rock where it can hover without getting blasted.
- Filtration: oversize it. These guys are messy carnivores and you will probably be feeding heavier foods (shrimp, squid, fish flesh).
- Temperature: cooler than a typical reef is usually better for deepwater species. If your system sits warm, consider a chiller or a dedicated cooler-water setup.
- Cover the tank: they wedge and launch. A tight lid saves heartbreak.
Bright lights plus no hiding spots equals a fish you basically never see, and one that often stops feeding. Give it darkness and a secure cave from day one.
What to feed them
They eat like a sneaky ambush predator. Mine would ignore food floating around in the open, then vacuum it up once it hit the bottom near its cave. You will get much better results if you target-feed after the main lights are off or during a blue/moonlight period.
- Best starter foods: small pieces of raw shrimp, squid, scallop, and marine fish flesh (sparingly).
- Frozen options: mysis (for smaller individuals), chopped krill, chopped clam. Soak and rinse if your frozen food is messy.
- Live foods (use carefully): live ghost shrimp can kick-start a new arrival, but do not make it a habit if you can avoid it.
- How I fed: long feeding tongs or a turkey baster, placing food right at the cave entrance.
- Schedule: small meals 3-5 times a week beats huge dumps. They will gorge if you let them, and your nutrients will show it.
Train it onto frozen by offering the same food at the same spot every time. Once it learns the routine, it will start poking its head out when you approach the tank at "feeding time" (usually after lights out).
How they behave and who they get along with
Expect a shy, nocturnal fish. During the day mine was basically a rumor. At night it would cruise slowly, then park itself and wait. They are not fast, not competitive, and they do not handle pushy tankmates well.
- Best tankmates: calm, non-competitive fish that will not steal every bite (think mellow deepwater or low-light fish).
- Avoid: aggressive feeders (triggers, big wrasses), nippy fish, and anything that will bully it out of its hiding spot.
- Also avoid: tiny fish and shrimp you are attached to. If it can fit in the mouth, it is on the menu sooner or later.
- Inverts: large snails and urchins are usually ignored, but small crabs and shrimp can disappear at night.
Most losses I have seen were not "mystery deaths". They were slow starvation because the brotula never got food past faster tankmates.
Breeding tips
Breeding them in home aquariums is not something you should count on. Deepwater live history plus limited captive populations makes it a long shot. I have never seen a confirmed hobbyist spawning for this species, and most reports are just "they got fat" or "they disappeared for a week" type observations.
If you ever do try, your best angle is a dedicated, low-light species tank with rock caves, very steady temperature, and heavy feeding for months. Even then, do not be surprised if nothing happens.
Common problems to watch for
This fish will usually tell you what is wrong, but it does it quietly. If it stays sealed in a cave for weeks and never comes out to feed, something in the setup is off or it is being outcompeted.
- Refusing food: often caused by too much light, not enough cover, or aggressive tankmates. Try feeding later, dimming the tank, and target-feeding at the cave entrance.
- Shipping/collection stress: deepwater fish can arrive in rough shape. Give it a low-stress quarantine with lots of hiding spots and minimal light.
- Rapid breathing: can point to ammonia/nitrite, low oxygen, or gill damage. Check water quality immediately and increase aeration.
- Skin damage from rockwork: they wedge hard into tight holes. Smooth any sharp rock edges near their favorite cave and keep rubble from shifting.
- Parasites: watch for flashing, excess mucus, or weight loss despite eating. Quarantine is your friend because treating a display full of inverts is a pain.
- Nutrient spikes: chunky seafood diets can foul water fast. Rinse frozen foods, feed smaller portions, and keep up with mechanical filtration maintenance.
Do not buy one unless you can give it a calm, dim environment and you are willing to target-feed. In a bright, busy community tank, it is the kind of fish that slowly fades away while everything else looks fine.
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