Longhead grenadier
Coelorinchus longicephalus
The Longhead grenadier features an elongated body with a tapered head, translucent skin, and prominent eyes that enhance its deep-sea adaptation.
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About the Longhead grenadier
This is a deep-sea rattail (grenadier) from the Northwest Pacific that lives way down on the slope, not something that can be kept in a normal aquarium. It gets a long, tapering body with that classic whiptail look, and it is built for cold, high-pressure water and cruising just off the bottom hunting small prey.
Also known as
Quick Facts
Size
89 cm TL
Temperament
Peaceful
Difficulty
Expert
Min Tank Size
1000 gallons
Lifespan
unknown
Origin
Northwest Pacific
Diet
Carnivore - small fishes and bottom-living crustaceans
Water Parameters
2-6°C
7.8-8.4
8-12 dGH
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This species needs 2-6°C in a 1000 gallon tank. Use our heater calculator to find the right wattage.
Calculate heater sizeCare Notes
- Real talk: a longhead grenadier is a deep-sea fish and basically not a normal-home-aquarium animal - it wants cold water (around 39-50F / 4-10C), dim light, and high oxygen, so you are looking at a chiller-driven coldwater marine system and serious flow.
- Give it a big, open footprint tank because it cruises and spooks easily; keep decor low and smooth (sand or fine grit, no sharp rock piles) so it does not shred that long tail when it bolts.
- Keep salinity stable at 1.024-1.026 and do not let nitrate creep up; these guys are touchy about dirty water and low oxygen, so oversize skimming and run extra aeration at night.
- Feeding is meaty and simple: small chunks of shrimp, squid, clam, silversides, and other marine flesh, plus the occasional live or thawed mysis/krill; target-feed with tongs after lights-out so faster fish do not steal everything.
- Avoid aggressive or hyper tankmates (triggers, large wrasses, puffers) because they will harass and fin-nip; stick with calm, coldwater-compatible species that will not outcompete it at feeding time.
- Watch for barotrauma and decompression damage if it was collected from depth (floaty behavior, bulging eyes, odd buoyancy) - many never fully recover, so buy only from a source that has properly decompressed and held the fish for a while.
- Breeding in captivity is basically a non-starter for hobbyists; they are deepwater spawners with larval stages you are not going to raise in a home setup, so plan on keeping a single specimen and just keeping it eating steadily.
Compatibility
Good Tankmates
- Other small, peaceful deepwater types that mind their own business - think rattails/grenadiers of similar size and temperament (as long as the tank is big and youve got lots of open bottom).
- Calm, non-predatory benthic fish like small-to-medium bristlemouths or other mellow bottom cruisers (basically anything that is not going to harass it or outcompete it at feeding time).
- Peaceful midwater planktivores that dont pick on bottom fish - things like smaller anthias-type community fish in a big, stable marine setup (they keep to the water column and wont bother it).
- Chill, non-aggressive sharks and rays that are too big to see it as food and arent pushy at meals (only in a huge system, and only if feeding is managed so the grenadier actually gets its share).
- Non-nippy scavengers like cleaner shrimp and most snails that wont hassle a resting fish - theyre usually fine and can help with leftovers from its meaty diet.
Avoid
- Aggressive or territorial predators like groupers, big snappers, or large predatory wrasses - theyll either bully it nonstop or eventually try to eat it.
- Nippy, pushy fish like big triggerfish and many larger puffers - they tend to bite fins and theyre absolute pigs at feeding time, so the grenadier gets stressed and starves out.
- Anything small enough to be swallowed (tiny gobies, small blennies, little cardinalfish) - peaceful or not, if it fits in the mouth, it becomes a late-night snack.
Where they come from
Longhead grenadiers (Coelorinchus longicephalus) are deepwater rattails. Think slope and deep benthic zones, not reefs. They spend their lives in dim light over soft bottoms, cruising slowly and sniffing out food with that long snout and barbels.
This is one of those fish that looks like it should be easy because it is calm. It is not. The challenge is mimicking deepwater conditions and getting a recently imported animal eating.
Setting up their tank
If you have not run a chilled marine system before, plan that first. Temperature is the whole game with deepwater grenadiers. Warm reef temps usually end in a slow decline even if the fish eats for a while.
- Tank size: bigger is your friend. I would not bother under 180-240 gallons just for swimming room and stability.
- Temperature: aim cold. Many keepers target roughly 45-55F depending on collection depth. Pick a number and keep it steady.
- Filtration: oversized skimmer plus strong biological filtration. These fish eat meaty foods and the tank gets dirty fast.
- Flow: moderate, not a blasting SPS setup. You want good turnover without pinning the fish behind rocks.
- Lighting: subdued. Dim lights and shaded areas help them settle and feed sooner.
Go easy on rock piles. They are not a cave-dweller like an eel, but they do like structure to break up sight lines and a calm corner to hover in. I like a mostly open footprint with a few low rock islands and a wide sand or fine rubble zone.
Cover every intake and overflow. Grenadiers are curious, slow swimmers and will nose into trouble. A simple coarse sponge prefilter can save you a disaster.
Acclimation is where people lose them. They are deepwater fish, so they may arrive stressed and touchy. Give them a quiet quarantine with the same cold temp, lots of oxygen, and zero chasing with nets.
What to feed them
They are carnivores that pick off small crustaceans and worms. In captivity, you are basically running a coldwater predator feeding program: small, meaty, frequent, and clean.
- Best starters: live blackworms (rinsed), live mysis, or live ghost shrimp if they will take them
- Once feeding: thawed mysis, chopped shrimp, chopped clam, squid strips, scallop, pieces of marine fish
- Helpful trick: soak food in a strong-smelling attractant (like clam juice) at first
Target feeding makes life easier. Use long feeding tongs or a feeding stick and place food right in front of the snout. They are not fast, and pushy tankmates will steal everything.
If it is ignoring frozen food, try tiny pieces. A lot of deepwater imports act like the food is too big even when it is not. Once they recognize it, you can size up.
Watch the belly line. A grenadier can look "fine" from above and still be wasting. I like smaller meals 4-6 days a week rather than one big dump that fouls the water.
How they behave and who they get along with
Temperament-wise, they are pretty mellow. They cruise, hover, and investigate the sand. The problem is not aggression, it is competition and stress.
- Good tankmates: other coldwater, calm fish that do not pester them and will not outcompete them at feeding time
- Avoid: aggressive predators, fast midwater feeders, fin-nippers, and anything that will pick at a slow, delicate fish
- Also avoid: warmwater species. Mixing temperature needs usually ends with someone losing.
They can eat small fish and shrimp if it fits. Not in a lightning strike way, more like a slow ambush or nighttime vacuuming. If you are attached to a tiny goby or decorative shrimp, do not gamble.
Stress shows up as hiding nonstop, refusing food, and that washed-out look. Give them quiet time. If you keep walking up to the glass and flipping bright lights on, they often go backward.
Breeding tips
Realistically, breeding longhead grenadiers in home aquariums is not a thing right now. They are deepwater spawners, likely broadcast spawners, and larval rearing would be a whole separate science project even if you got eggs.
If you keep one long term, that is already a win. Focus your energy on temperature stability, low stress, and getting it feeding reliably.
Common problems to watch for
- Temperature creep: the tank slowly warms up over weeks (or the chiller cycles too wide) and the fish fades over time
- Shipping damage and pressure-related issues: poor buoyancy, weird posture, lethargy right after arrival
- Starvation in disguise: it "acts normal" but loses weight because it never gets enough food in a community tank
- Mouth and snout injuries: from ramming the glass, rock, or getting pinned to an intake
- Bacterial infections after stress: frayed fins, red sores, cloudy eyes in a fish that was recently imported
- Water quality swings: meaty foods plus cold water can still mean ammonia problems if the biofilter is not mature
The biggest red flag is a fish that will not start feeding within the first couple of weeks. Some take longer, but you should see curiosity around food, sniffing, or at least a few tentative bites. If it is totally uninterested, I lower stress, dim the tank, and go back to live foods and target feeding.
Do not buy one unless you can run a stable chilled marine system long-term. A "cool room" and a fan is not the same thing. These are deepwater animals and they usually do not forgive warm spells.
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