Faustino's lanternfish

Where they come from

Faustino's lanternfish (Diaphus faustinoi) is a mesopelagic lanternfish - one of those deep-ocean, glow-in-the-dark types that spends its life in the dim "twilight zone" of the sea. They do daily vertical migrations in the wild (up at night, down in the day), and that single fact drives almost everything about keeping them.

Setting up their tank

Think "cold, dark, quiet, and stable" more than "reef showcase." A standard warm reef tank is a fast track to a dead lanternfish. You want a dedicated system where you control temperature and light and you are not fighting the rest of a mixed community.

• Tank size: I would not bother under 40-55 gallons for a single fish, bigger if you want a small group. They are midwater cruisers, not perchers.
• Temperature: chilled. Aim roughly 50-60F (10-16C) unless you have confirmed collection depth/region data. Warm water knocks them out fast.
• Salinity: normal marine range (around 1.024-1.026), but keep it steady more than "perfect."
• Lighting: very low. I use dim ambient room light or heavily shaded LEDs. Bright reef lighting keeps them stressed and pinned to corners.
• Flow and filtration: gentle, even flow. Strong jets make them burn energy and slam into glass. Oversize filtration helps because you will be feeding small, messy foods often.
• Aquascape: open water with a few dark "edges" (caves/overhangs or black background) so they feel they have somewhere to fade back into. Avoid sharp rockwork they can spook into.
• Cover: tight lid. Spooked deepwater fish can jump, and you will not get a second chance.

Acclimation is where most attempts fall apart. Go slow on temp and salinity, keep the bucket dark, and avoid blasting them with a flashlight. If the fish is floating oddly or rolling, stop fussing and get it into stable, oxygen-rich water quickly - endless drip acclimation can be worse than a controlled, shorter one for a fish that is already stressed.

What to feed them

They are micro-predators. In my experience, the biggest hurdle is getting consistent feeding response under aquarium lighting. Once they recognize food, they tend to be steady eaters, but you have to meet them where they are: small items drifting in the water column, mostly at "night."

• Best starter foods: live enriched baby brine (not as a long-term staple), live copepods, live mysis if you can get small ones.
• Frozen foods that often work after training: PE calanus, finely chopped mysis, chopped krill (tiny bits), cyclops, fish eggs/roe.
• Enrichment: soak in HUFA (Selco, etc.) and add vitamins occasionally. Deepwater fish seem to crash faster when nutrition is skinny.
• Feeding schedule: small amounts 2-4 times a day is better than one big dump. I do most feedings in low light or after lights out.

How they behave and who they get along with

Lanternfish are shy, midwater fish that spend a lot of time hovering and making short, careful darts. They spook easily. A calm tank and predictable routine matters more than people expect.

Tankmates are where most hobby setups go sideways. You are basically choosing between "species-only" or "very carefully selected coldwater, low-light companions." Anything boisterous, territorial, or fast at feeding time will stress them or outcompete them.

• Good idea: species-only, or a small group of the same lanternfish if your tank is large and you can keep up with feeding.
• Maybe: other peaceful, chilled-water planktivores with similar feeding speed (rare in the hobby).
• Bad idea: aggressive fish, most wrasses, damsels, dottybacks, triggers, big hawkfish, and anything that treats small fish like snacks.
• Also bad: bright reef setups with bustling tangs and anthias. The lanternfish will act like a ghost and waste away.

Breeding tips

Realistically, breeding Diaphus in home aquariums is in the "nice dream" category. In the wild they spawn in open water, larvae are planktonic, and their life cycle is tied to depth, light cues, and probably seasonal rhythms we do not replicate.

If you ever did want to take a swing at it, you would be looking at a chilled, dim system with extremely stable parameters, a well-fed group, and a way to collect pelagic eggs/larvae (think gentle overflow to a collector). But I have not seen reliable reports of home-bred lanternfish for a reason.

Common problems to watch for

• Heat and bright light stress: rapid breathing, hiding constantly, refusing food, frantic swimming when lights change.
• Starvation in disguise: they may look "normal" while slowly losing weight. Watch the belly line and overall fullness, not just whether they peck once in a while.
• Shipping/collection damage: poor buoyancy control, rolling, head-up or tail-up floating, sudden crashes in the first week.
• Bacterial issues after rough import: frayed fins, red patches, cloudy eyes. Quarantine is tricky because they hate bright bare tanks, so plan a dark, chilled QT with lots of oxygen.
• Water quality swings: because you feed small planktonic foods often, nutrients creep up fast. If you let ammonia/nitrite appear even briefly, they tend to spiral.
• Mechanical injuries: they spook into glass or rock. Sharp aquascape edges and strong flow make this more likely.

If you are determined to keep Faustino's lanternfish, the biggest wins are: keep it cold, keep it dim, keep it calm, and get it eating early. Everything else is details. If you want, tell me your tank size and what temps you can realistically hold, and I can suggest a setup that matches your gear.