Spothead lantern fish

Where they come from

Spothead lanternfish (Diaphus metopoclampus) are deepwater mesopelagic fish. They spend daylight way down in the dark and then migrate upward at night to hunt. That whole "live in the twilight zone" lifestyle is basically the reason they are so hard to keep.

Setting up their tank

If you try to keep these like a normal reef fish, you'll just watch them fade. Think cold, dim, quiet, and stable. They handle "pretty" tanks badly and "boring" tanks well.

• Tank size: bigger is easier, not because they get huge, but because stability matters. I would not bother under ~75 gallons, and 120+ gives you room to control light and flow.
• Temperature: cool water. Aim roughly 50-60F (10-16C). This usually means a serious chiller and insulation.
• Lighting: very low. Start with near-dark and slowly bring up a faint blue if you want to see them. Bright reef lighting will keep them pinned and stressed.
• Aquascape: open water with a few dark overhangs. You want them to feel like there is "depth" even if the tank is shallow.
• Flow and oxygen: moderate, smooth flow and high dissolved oxygen. Cold water helps, but you still want strong gas exchange and a skimmer.
• Filtration: oversized skimming and aggressive mechanical filtration. These fish like frequent small feedings, and that makes nutrients climb fast.
• Lid: tight-fitting. Lanternfish can jump, especially during night-time activity bursts.

Acclimation matters more than most fish. I do a slow drip, keep the bucket dim, and I do not chase them with nets. A soft specimen container is your friend. If they arrive with obvious barotrauma (bloated, floating, eyes bulging), your odds aren't great.

What to feed them

This is the make-or-break part. They are built to pick off tiny crustaceans in the water column. Many will ignore flakes and pellets completely, especially early on.

• Best starter foods: live copepods, live enriched Artemia (adult brine), live mysis if you can get it.
• Frozen that often works after they settle: small mysis, calanus, cyclops, finely chopped krill (sparingly), roe.
• Enrichment: HUFA enrichment on live foods helps a lot. I treat it like feeding mandarins: you want nutrition density, not just "stuff moving."
• Feeding schedule: small amounts multiple times, especially around their "night" period. One big dump of food usually means wasted food and dirty water.

Watch their body shape. A lanternfish that is eating stays nicely filled out behind the head and along the belly line. If it starts looking pinched, you need to change something fast: food size, timing, or competition.

How they behave and who they get along with

They are shy, midwater fish that do most of their real activity in dim conditions. In a bright tank they'll hover, hide, or just burn energy trying to stay invisible. In a dim tank, you'll see that classic lanternfish cruising and quick dart-feeding.

• Best tankmates: other coldwater, low-light, non-competitive planktivores. Think small, calm species that won't mug them at feeding time.
• Avoid: aggressive feeders (anthias types, many damsels), anything that nips, and anything large enough to inhale them.
• Group or solo: they can do fine in small groups if the tank is big and feeding is frequent. In cramped quarters, the timid ones lose out.

Breeding tips

Realistically, breeding spothead lanternfish in home aquaria is a long shot. They are pelagic spawners, and their larvae are tiny, drift-feeding plankton specialists. You would be looking at a dedicated live plankton pipeline and a very controlled light and temp regime.

Common problems to watch for

• Shipping and pressure damage: barotrauma, internal injuries, sudden death within days. This is collection-related and hard to fix once it happens.
• Starvation: the most common slow failure. They "act normal" but get thinner. Fix with smaller foods, more frequent feeds, dimmer conditions, and less competition.
• Light stress and collision injuries: scraped snouts, torn fins, frantic dashing when lights change. Use gentle ramps and keep the room dark at night.
• Bacterial issues after damage: cloudy eyes, red sores, fin rot. These fish do poorly with rough handling, so prevention beats treatment.
• Water quality swings: they do not like big salinity/temperature/pH moves. In cold systems, heaters/chillers and top-off mistakes can bite you fast.

If you want a quick reality check before you buy: ask yourself if you can keep a cold, dim marine system stable, feed live foods on a schedule, and protect them from bright-room chaos. If yes, they are fascinating fish to observe. If not, they usually end up as a lesson rather than a success.