Spotfin cusk
Neobythites macrops
The Spotfin cusk exhibits a slender body with a dark brown coloration and distinct pale spots, accented by a long, continuous dorsal fin.
This page includes AI-generated images. Why am I seeing AI images?
About the Spotfin cusk
Neobythites macrops is a deep-slope cusk-eel from the Indo-West Pacific that hangs out way down on the shelf and upper slope. It is one of those long, eel-ish bottom fish with little eyespots (ocelli) on the dorsal fin - cool camouflage/decoy stuff for life in dim water. Not really an aquarium fish in any normal sense, since it is a true deepwater marine species.
Also known as
Quick Facts
Size
21.6 cm SL
Temperament
Peaceful
Difficulty
Expert
Min Tank Size
180 gallons
Lifespan
unknown
Origin
Indo-West Pacific
Diet
Carnivore - small fishes and crustaceans (typical deepwater demersal predator)
Water Parameters
4-12°C
8-8.4
8-12 dGH
Need a heater for this species?
This species needs 4-12°C in a 180 gallon tank. Use our heater calculator to find the right wattage.
Calculate heater sizeCare Notes
- Give it a dim, cave-heavy setup with lots of tight rock crevices and a sandy patch - they want to wedge in and peek out, not cruise open water. Cover every gap because they can snake into overflow boxes and plumbing.
- Keep it cool-ish for a reef fish: aim around 72-76F with steady salinity 1.025-1.026 and a stable pH around 8.1-8.3. They sulk and go off food fast when nitrate creeps up or the tank swings day to day.
- Feed after lights-out: small meaty stuff like mysis, chopped shrimp, clam, and enriched brine, plus the occasional live blackworm or ghost shrimp to kick-start picky new arrivals. Use a feeding stick and drop food right at the cave entrance so faster fish do not steal it all.
- Skip aggressive or hyper-active tankmates - triggers, larger wrasses, dottybacks, and hawkfish will harass it or outcompete it at dinner. Safer picks are calm, non-predatory fish that will not camp its cave or bully it off the bottom.
- Assume anything tiny that fits in its mouth is food, including small gobies and ornamental shrimp. Crabs can also be a problem because they will steal food and sometimes pinch when the cusk is wedged in.
- Run strong mechanical filtration and stay on top of detritus because they are messy carnivores and like low-flow pockets where junk builds up. If you see heavy breathing or lots of yawning, check oxygen and flow at the cave area, not just in the display.
- Quarantine is worth the hassle - they can come in with flukes and other parasites and they do not handle harsh copper well. If you have to treat, go gentle and watch appetite closely because once they stop eating they spiral fast.
- Breeding in home tanks is basically a lottery - they are secretive, likely pair up in deep caves, and eggs/larvae are not straightforward to raise. If you ever see a pair guarding a hole, leave them alone, keep feeding heavy at night, and do not rearrange rockwork.
Compatibility
Good Tankmates
- Small, mellow gobies (neon gobies, clown gobies, trimma/eviota types) - they hang out in their own little zones and dont hassle a shy cusk
- Firefish and dartfish (Nemateleotris) - peaceful, open-water floaters that wont compete for caves or pick at them
- Cardinalfish (Banggai or pajama) - calm, midwater, and not the type to bully a reclusive fish that likes dim corners
- Small, laid-back wrasses like a possum wrasse (Wetmorella) - good temperament and usually ignores bottom cave dwellers
- Blennies that mind their own business (tailspot, bicolor, etc.) - generally fine as long as the blenny is not a terror about its hole
- Peaceful inverts like cleaner shrimp, peppermint shrimp, and smaller hermits/snails - usually safe if your spotfin cusk is well fed and not tiny with a huge mouth gap
Avoid
- Dottybacks and pseudochromis (especially orchid dottyback types that still get spicy) - they love the same rockwork and will run a shy cusk into hiding 24/7
- Hawkfish - perch-and-pounce personalities, can harass or outright eat smaller tankmates and shrimp, not a great vibe for a peaceful cusk
- Big or pushy wrasses (sixline, many Halichoeres, etc.) - constant motion and rock picking stresses them, and the bolder ones will bully anything timid
- Aggressive damselfish and clownfish that have claimed the whole tank (domino damsels, maroons, territorial clowns) - nonstop chasing and fin nipping is what you are trying to avoid
Where they come from
Spotfin cusk (Neobythites macrops) are deepwater cusk-eels from the Indo-Pacific. Think dim slopes, rubble, and little caves - not bright reef flats. That deepwater background explains almost everything about how they act in an aquarium: shy, low-light, and very tuned in to food smells.
If your fish shows up looking a bit beat up from shipping, you are not alone. Deepwater fish often arrive stressed, and the first 2 weeks are the make-or-break window.
Setting up their tank
This is an expert fish mostly because of acclimation and long-term stability, not because it needs fancy gadgets. You are trying to recreate a calm, dim, secure spot where it can wedge itself and feel safe.
- Tank size: I would not do one in anything under 55 gallons. Bigger helps keep parameters steady and gives it multiple hiding zones.
- Aquascape: rockwork with actual caves and narrow crevices. PVC elbows hidden behind rock work too, and they will use them.
- Substrate: fine sand is nice. They sometimes rest on it, and coarse gravel can scrape them up.
- Flow: moderate, not blasting the caves. Give it quiet pockets.
- Lighting: keep it subdued or give heavy shaded areas. They are way bolder under blue-only evenings or dim lighting.
- Filtration: strong biological filtration and a skimmer. These guys like meaty foods and that adds up fast.
- Cover: tight lid. They can dart and launch when spooked, especially during the first week.
Acclimation matters. I treat them like delicate imports: slow drip, match salinity carefully, and keep the lights off the rest of the day. A bright tank plus a net chase is a bad combo with this fish.
If you can run your tank a touch cooler than a typical tropical reef, do it. I have had better appetites and calmer behavior in the mid 70s F rather than pushing 80F. Stability beats chasing a number, though.
What to feed them
They are predators that hunt by smell and vibration. Expect a fish that might ignore flakes and pellets at first, then suddenly become a pig once it recognizes your feeding routine.
- Best starters: thawed mysis, finely chopped shrimp, clam, squid, and strips of marine fish flesh.
- Once settled: larger mysis, chopped krill, enriched brine (as a treat), and good frozen blends.
- How I get them going: feed after lights out with a turkey baster or feeding stick and aim the food right at the cave entrance.
- Frequency: small portions 4-6 times a week beats one huge dump. They are easy to overfeed and your nutrients will tell you fast.
If it is refusing food, try fresh clam or live ghost shrimp for a day or two just to flip the switch. Once it eats reliably, transition back to frozen so you are not stuck buying live forever.
Watch the mouth size and adjust chunks accordingly. Big pieces get grabbed, chewed, and spit repeatedly, which can foul the water and make you think it is not eating.
How they behave and who they get along with
Most of the time you will see a head poking out of a hole, especially during the day. At dusk they come alive and patrol short routes between hideouts. They are not a show fish unless you set the tank up around their comfort.
- Temperament: generally peaceful, but will eat anything that fits in its mouth.
- Good tankmates: calm fish that will not harass a cave-dweller (tangs, larger wrasses that are not bullies, rabbitfish, peaceful angels).
- Avoid: dottybacks, aggressive damsels, big hawkfish, triggerfish, and anything that likes to pick at resting fish.
- Invert safety: tiny shrimp and small crabs can become food. Big cleaner shrimp are a coin flip depending on size and the individual fish.
Do not keep it with super fast, pushy eaters unless you are willing to target feed. A cusk that misses meals for a week can go downhill quietly.
They also do better with more than one hide. If their only cave is right next to the busiest part of the tank, they will stay locked up and you will barely see them.
Breeding tips
Breeding in home aquariums is basically a long shot. Sexing is not straightforward, pairs are hard to source, and many deepwater species have larval stages that are not realistic without serious live plankton cultures and space.
If you ever see two sharing a den and doing gentle shoving or circling at dusk, that is the closest thing to courtship behavior I have seen. Even then, raising larvae would be the real challenge.
Common problems to watch for
- Shipping and decompression stress: heavy breathing, refusing food, laying awkwardly. Keep the tank quiet and dim and focus on oxygenation and stable water.
- Starvation in plain sight: they can look 'fine' while slowly losing weight. Check the body behind the head - you want some thickness, not a pinched look.
- Bullying and fin damage: torn fins and constant hiding usually means a tankmate is messing with it at night.
- Jumping: usually during the first week or after a scare. A tight lid fixes most of this.
- Parasites (ich/velvet): deepwater fish can come in with baggage. Quarantine if you can, and do not medicate blindly in the display.
- Water quality swings: meaty foods spike nutrients. If nitrates and phosphate creep up, the fish may get lethargic and stop feeding.
Velvet can move fast. If you see rapid breathing, dusting, or it is hanging in high flow gasping, treat it like an emergency and act the same day.
My best advice is to treat this species like a shy, nocturnal ambush predator that wants a calm corner and regular, targeted meals. If you give it dim shelter and keep the tank stable, it settles in and becomes a really cool, oddball resident.
Similar Species
Other marine peaceful species you might be interested in.
Abe's eelpout
Japonolycodes abei
Japonolycodes abei is a temperate, deepwater demersal eelpout (family Zoarcidae) endemic to Japan (Kumano-nada Sea reported; other sources also report Sagami Bay and Tosa Bay). It is the only species in the genus Japonolycodes and occurs roughly 40-300 m depth, making it an uncommon/atypical aquarium species.
Affinis blind cusk-eel
Barathronus affinis
Barathronus affinis is a tiny, super-weird deep-sea blind cusk-eel from the western-central Indian Ocean. It is one of those gelatinous, loose-skinned brotula-type fishes that live way down in the dark and are basically never seen alive, so almost everything we know comes from preserved specimens and taxonomic work.
Annandale's zebra sole
Zebrias annandalei
Zebrias annandalei is a small, bottom-hugging sole from coastal India that lives on sandy/muddy flats and spends its life glued to the substrate. Its whole deal is camouflage and "disappearing" behavior like other soles - cool fish, but not really a typical home-aquarium species and you would need a proper marine sand-bottom setup to even try it.
Banggai Cardinalfish
Pterapogon kauderni
Banggai cardinals just sort of hover like little underwater satellites, and the bold black bars with those long, polka-dotted fins look unreal under reef lighting. They're super chill most of the time, but once a pair forms you'll see real "fish drama," and the male will even mouthbrood the babies like a champ.
Barbedwire-tailed skate
Notoraja martinezi
Notoraja martinezi is a deepwater skate from the eastern Pacific (Costa Rica down to Ecuador) that lives way down on soft bottoms. The tail is the giveaway - it is lined with strong, hooked thorns that really do look like barbed wire. This is absolutely not an aquarium fish; it is a cold, high-pressure deep-sea animal with basically no practical home care info because it is not kept in the hobby.
Ben-Tuvia's goby
Didogobius bentuvii
This is a tiny little Mediterranean goby from the Israeli coast that lives down on the bottom over muddy-sand, and it is likely a burrower. In other words, it is a blink-and-you-miss-it kind of fish - super small, demersal, and more about sneaky bottom-dweller vibes than flashy swimming.
More to Explore
Discover more marine species.
African red snapper
Lutjanus agennes
This is a true snapper from West Africa - a big, fast-growing predator that goes from coastal reefs to brackish lagoons and estuaries (especially as a juvenile). Super cool fish in the wild, but it gets absolutely huge and will eat smaller tankmates once it has the mouth for it, so its really more of a public-aquarium scale animal than a home-aquarium fish.
Aleutian skate
Bathyraja aleutica
This is a big, cold-water deep-slope skate from the North Pacific that cruises muddy bottoms and eats chunky benthic prey like crabs and shrimp. The really cool bit is its egg-laying skate life - it does distinct pairing (the classic skate "embrace") and drops those tough egg cases on the seafloor. Not an aquarium fish at all unless you're basically running a public-aquarium-style chilled system.
Arabian spiny eel
Notacanthus indicus
Notacanthus indicus is a deep-sea spiny eel (family Notacanthidae; not a true eel) known from the Arabian Sea on the continental slope at roughly ~960–1,046 m depth, with reported maximum length around 20 cm TL; it is a deep-water bycatch species and not established in the aquarium trade.
Arctic rockling
Gaidropsarus argentatus
This is a deepwater North Atlantic rockling (a cod relative) that hangs out on soft bottoms way down the slope. It is a cold-water, bottom-hugging predator that snoots around for crustaceans and will also take small fish when it gets the chance.
Atlantic pomfret
Brama brama
Brama brama is the Atlantic pomfret (aka Ray's bream) - a deep-bodied, open-ocean pelagic fish that cruises around in small schools and follows water temps. It is a legit big, wild marine species (not an aquarium fish) that eats other small sea critters like fish and squid, and it ranges across a huge chunk of the Atlantic plus parts of the Indian and South Pacific.
Australian sawtail catshark
Figaro boardmani
Figaro boardmani is a small, deepwater Australian catshark with these cool saw-like ridges of spiny denticles along the tail and a neat pattern of dark saddle bands. It lives way down on the outer continental shelf and slope, so its natural water is cold, dim, and stable - totally not a typical home-aquarium fish. Diet-wise its a predator that goes after fish, crustaceans, and cephalopods.
Looking for other species?