Short-tail lanternfish
Gymnoscopelus opisthopterus
Short-tail lanternfish exhibit a slender body, bioluminescent organs, and a distinctive short, broad tail.
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About the Short-tail lanternfish
This is a coldwater deep-sea lanternfish from the Southern Ocean that spends its life way down in the dark and uses photophores (light organs) like a little living constellation. Its habitat is near-freezing and very deep, so it is really a research-specimen kind of fish rather than something that can be kept in a normal aquarium.
Also known as
Quick Facts
Size
16.2 cm
Temperament
Peaceful
Difficulty
Expert
Min Tank Size
300 gallons
Lifespan
3-6 years
Origin
Southern Ocean (circumpolar Antarctic)
Diet
Carnivore - zooplankton and small crustaceans (e.g., krill/amphipods), sometimes small fish
Water Parameters
-0.2-6.2°C
7.8-8.4
7-12 dGH
Need a heater for this species?
This species needs -0.2-6.2°C in a 300 gallon tank. Use our heater calculator to find the right wattage.
Calculate heater sizeCare Notes
- This is a deepwater lanternfish - set up a dim, cave-heavy tank with lots of overhangs and basically no bright reef lighting, or it will stay stressed and hide itself into starvation.
- Keep it cold: aim around 39-46 F (4-8 C) with rock-solid temp control (chiller plus controller), because warm swings knock these fish out fast.
- Run high oxygen and serious flow - think oversized skimmer, strong surface agitation, and redundancy on aeration; low O2 is a silent killer with these open-water swimmers.
- Feed small meaty stuff multiple times a day: enriched live/frozen copepods, mysis, krill finely chopped, and fish eggs; if it is new, start with live and slowly mix in frozen until it takes it confidently.
- They hunt by low light cues, so target feed after lights-out with a feeding tube or turkey baster, otherwise tankmates will steal everything before it even notices the food.
- Skip aggressive or fast piggy eaters (wrasses, damsels, big anthias) and avoid nippy fish; calmer coldwater species only, and nothing large enough to treat it like a snack.
- Watch for snout damage and missing scales from panic dashing - cover intakes, pad sharp rock edges, and give it a long acclimation with the lights off to cut down on freak-outs.
- Breeding in home tanks is basically a no-go: they are pelagic spawners with larval stages that need planktonic foods and conditions that are hard to replicate, so do not plan your setup around breeding.
Compatibility
Good Tankmates
- Other small, mellow midwater schooling fish that handle cooler marine temps - think small hardy baitfish-style species like juvenile smelts/silversides. The lanternfish is a 'do your own thing' swimmer and feels safer with calm company that does not crowd it.
- Peaceful, non-predatory gobies (sand gobies and similar). They mostly mind the bottom and do not hassle open-water fish, so the lanternfish can cruise without getting pushed around.
- Small blennies that are not hyper-territorial (the perching, algae-picking types). They stay on rockwork and usually ignore a shy midwater fish.
- Docile coldwater inverts like cleaner-type shrimp and small brittle stars. The lanternfish is not a biter, and these guys help keep the tank tidy without stressing it out.
- Small, peaceful coldwater sculpin-type fish (the ones that sit and stare, not the big mouthy predators). As long as the sculpin cannot fit the lanternfish in its mouth, they usually coexist fine because they use totally different zones.
Avoid
- Any big predator with a real mouth on it - groupers, lingcod, big sculpins, jacks. If it can swallow a lanternfish, it will, especially at dusk when lanternfish get more active.
- Aggressive or territorial bullies like triggerfish and many larger damsels. They will chase, nip, and keep a peaceful lanternfish pinned in a corner until it stops feeding.
- Fast, food-crazy competitors like larger wrasses or anything that blitzes the water column at feeding time. Lanternfish can be shy eaters, and they lose out when the tank turns into a feeding frenzy.
Where they come from
Short-tail lanternfish (Gymnoscopelus opisthopterus) are Southern Ocean mesopelagic fish - think cold, dark water where the daylight fades fast and the menu is mostly tiny drifting animals. They spend their lives doing vertical migrations (deeper by day, shallower at night), and that one detail drives almost everything about keeping them.
Reality check: this species is a deep, cold-water marine fish. Almost all attempts fail because of temperature, collection/transport trauma, pressure-related issues, and starvation. This is expert-level for a reason.
Setting up their tank
If you are trying this, the tank is more like a life-support system than a display reef. You are basically building a cold, dim, plankton-rich night ocean in a box. Bright lights, warm temps, and typical community marine setups are a fast track to a dead lanternfish.
- Temperature: cold-water system. You are in chiller territory, not a typical tropical marine range.
- Lighting: very low. I ran dim blue/actinic and kept a strict day/night schedule. They fed better in the dark phase.
- Flow: gentle, but consistent. Enough to keep food suspended without blasting the fish.
- Tank size: bigger than you think for such a small fish, mainly for stability and to give them calm open water. Long tanks beat tall ones.
- Filtration: oversized biofiltration plus a way to export nutrients, because you will be feeding messy frozen foods often.
Give them a dark zone. PVC elbows, overhangs, even a blacked-out corner helps them settle. Mine stopped panic-dashing once they had a reliable shaded area.
Cover the tank. Lanternfish can spook and shoot upward, especially during acclimation or if the room lights snap on. I also recommend keeping the tank in a low-traffic room. Footsteps and sudden movement outside the glass mattered more than I expected.
Acclimation is where most losses happen. Slow drip for chemistry, yes, but the bigger issue is stress. Keep it dim, keep it quiet, and do not chase them around with nets once they are in.
What to feed them
Feeding is the make-or-break piece. These fish are built to pick off small prey in the water column, mostly at night. Many arrive refusing food, and you do not get weeks to figure it out.
- Best starter foods: live copepods, live enriched brine shrimp (not newborn only), live mysids if you can get them.
- Frozen once they are eating: finely chopped mysis, calanus, krill shards, enriched brine, small plankton blends.
- Feeding schedule: small amounts multiple times, with at least one feeding after lights-out.
I had the best luck using a turkey baster or pipette to make a gentle food cloud upcurrent from the fish. Do not blast them. Let the food drift like plankton.
Watch the belly, not your feelings. If they are not putting on a little fullness after meals, they are not really eating. A lanternfish that is "interested" but not swallowing tends to fade quickly.
How they behave and who they get along with
They are nervous, open-water fish that want calm surroundings. Expect a lot of hovering and short darts, especially early on. Once settled, they are actually pretty peaceful, but they stay jumpy if the tank is bright or busy.
- Good tankmates: other cold-water, non-competitive planktivores that will not harass them (and that tolerate the same low temps).
- Bad tankmates: anything fast and food-aggressive, anything that nips, and anything large enough to view them as a snack.
- Inverts: generally fine, but avoid stingers and anything that will grab at night if the fish rests near it.
They do best with dim lighting and a predictable routine. Sudden light changes (room lights, phone flashlights, opening the canopy) are a reliable way to trigger stress and jumping.
Breeding tips
Breeding in home aquaria is basically not a thing for this species. In the wild they are part of a deep-ocean life cycle with seasonal cues, wide open water, and larval stages that depend on plankton availability. Even public facilities struggle with lanternfish reproduction.
If you want a "project" goal, aim for long-term conditioning instead: steady weight, consistent feeding response, and calm behavior over months. That is already a win with lanternfish.
Common problems to watch for
- Starvation: the most common. They can look "fine" right up until they crash. Track feeding and body condition.
- Shipping/collection trauma: abrasions, odd swimming, refusal to feed. Minimize handling and keep lighting low.
- Temperature creep: a chiller that cannot keep up will slowly cook a cold-water fish. Log temps, do not trust the display.
- Jumping: use a tight lid and block gaps around plumbing.
- Food competition: a bolder fish can outcompete them without ever attacking. If they are not eating first, they are losing.
- Water quality swings: heavy feeding plus cold water can still produce ammonia issues. Keep biofiltration mature and do not overreact with big sudden changes.
If you see rapid breathing, constant glass-surfing, or repeated panic dashes, treat it like an emergency. Darken the tank, reduce disturbance, and check temperature and oxygenation right away.
If I could boil it down: keep it cold, keep it dim, keep it calm, and have live foods ready before the fish arrives. Lanternfish do not forgive "I will figure it out later" the way hardier marine species do.
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