Suborbital lanternfish

Where they come from

Suborbital lanternfish (Diaphus suborbitalis) are mesopelagic fish - the kind that live out in the open ocean and spend their lives in the "twilight zone" (roughly a few hundred meters down). They migrate up and down in the water column with the day-night cycle, and they rely on low light, cooler water, and a steady supply of tiny drifting prey.

Setting up their tank

If you try one, you are basically building a life-support system first and an aquarium second. Think dim, cool, super stable, and very gentle flow. A deepwater biotope vibe works better than a bright reef.

• Tank size: bigger helps stability. I would not attempt under 75 gallons, and 120+ is where you get breathing room.
• Temperature: aim cool (mid to high 60s F). This usually means a chiller, not just a fan.
• Lighting: very dim. I used low-intensity blue and lots of shaded areas. Bright reef lights will keep them stressed and hiding.
• Filtration: oversized and quiet. Big skimmer, lots of biological capacity, and carbon on hand for "oops" moments.
• Flow: not a wave machine. Give them calm lanes to hover in and a few gentle current areas to bring food past them.
• Aquascape: open water is more useful than rock piles. Add a couple of caves/overhangs for security, but keep swim room.

Cover the tank. Lanternfish are jumpers, especially after lights change or if they get spooked. I also like a slow ramp up/down on lighting so you are not flipping them from night to day instantly.

What to feed them

Feeding is usually the make-or-break point. In the wild they pick off zooplankton all night. In captivity you are trying to replicate that with lots of small, meaty foods offered frequently, mostly in low light.

• Best starters: live enriched copepods, live adult brine (enriched), live mysis if you can get it small enough.
• Frozen once they recognize food: mysis (small), calanus, krill fines, chopped prawn, plankton blends.
• Pellets/flakes: usually a no, at least at first. Some individuals may convert later, but do not count on it.
• Feeding schedule: multiple small feedings. I had the best luck doing a heavier feeding after lights-out and a smaller one right before "dawn".

Watch the fish, not just the food. A lanternfish that is actually eating will make quick little darts and you will see the mouth snaps. If food is drifting by untouched night after night, you need to change something fast (lighting, flow, food type, or tankmates stealing it).

How they behave and who they get along with

They are shy, midwater fish that like the "safe" feeling of a group, but they also stress easily. Expect them to hang in the darker half of the tank and get more active at dusk and after lights-out.

• Temperament: peaceful, easily bullied.
• Best tankmates: other calm, cool-water, low-light species that will not outcompete them at feeding time.
• Avoid: aggressive fish, fast pigs at feeding (most wrasses, many damsels), and anything big enough to treat them as snacks.
• Group vs single: small groups can help confidence, but only if you can feed heavily and keep water quality stable.

If you are mixing species, run a red moonlight or very dim blue after main lights go off and feed then. Lanternfish tend to switch on at night, while a lot of typical tank fish settle down.

Breeding tips

Breeding Diaphus in home aquariums is basically in the "nice dream" category. They are open-ocean spawners, larvae are tiny and planktonic, and you would need specialized plankton culture and probably a kreisel-style larval system.

Common problems to watch for

Most issues come from stress and starvation, with water quality and temperature not far behind. Lanternfish can look "fine" right up until they crash, so you have to be a little paranoid with observation.

• Not eating: the big one. Usually caused by too much light, too much activity around them, wrong food size/type, or competition.
• Shipping/decompression damage: odd buoyancy, rolling, inability to stay level, sudden death in the first days.
• Temperature stress: kept too warm they burn energy fast and fade quickly, even if they eat.
• Mouth/skin injuries: from frantic dashing into glass during bright-light transitions or when spooked.
• Parasites: flashing, weight loss despite eating, excess mucus. Quarantine is hard with deepwater fish, but skipping it can be worse.
• Water quality swings: they do not handle salinity or pH swings well. Top-off and stable mixing habits matter a lot here.

My biggest practical takeaway: keep it calm, keep it cool, feed like you mean it, and do not treat them like a normal reef fish. If you cannot run a chiller and you cannot commit to frequent small feedings (especially at night), I would pass on this species.