Bigeye lightfish

Where they come from

Bigeye lightfish are mesopelagic wanderers found in tropical and subtropical oceans around the world. They hang out in the deep scattering layer by day and ride the nightly elevator up toward shallower water to chase plankton. Think 200-700 m most of the time, with big eyes and rows of tiny lights (photophores) to match that dim world.

• Range: pretty much global in warm seas
• Lifestyle: midwater, not reef-bound
• Daily routine: deeper by day, shallower at night

Setting up their tank

You want a quiet, dim, chilled midwater setup. They are easily spooked and do best in open water with gentle, even flow. Think more like a jellyfish kreisel than a coral tank.

• Volume: 150-300 liters for a small group. Bigger is easier to keep stable.
• Temperature: 14-18 C is the sweet spot in my experience. A reliable chiller is non-negotiable.
• Salinity: 34-35 ppt. pH 8.0-8.3. Keep it steady.
• Lighting: extremely dim. I black out three sides and use red film over a small inspection light. They hate bright, white light.
• Flow: wide, laminar flow. Avoid point-source jets. Round corners or a kreisel-style display helps prevent panic injuries.
• Cover: tight lid. They will bolt to the surface if startled.
• Aquascape: open water. A dark back and bottom (vinyl wrap or paint) cuts reflections. A little live rock in a sump is enough for biofiltration.
• Filtration: oversized skimmer and good mechanical filtration. You will feed a lot of fine foods and need to pull out the leftovers.
• Oxygen: keep O2 high. Cold water holds more oxygen, but I still run strong gas exchange and surface agitation.

Quarantine them in the same kind of dim, chilled conditions. Lights out for the first 24 hours, then peek with red light only. I drip acclimate slowly and keep the room dark the whole time.

What to feed them

They are midwater plankton pickers. Moving food flips the switch for them, especially after lights-out.

• Live foods to start: copepods (Acartia, Parvocalanus), small mysids, enriched Artemia nauplii. This gets them eating reliably.
• Frozen options once they settle: Calanus, Cyclops, finely chopped mysis, fish eggs. I target-feed with a long tube into the midwater.
• Feeding schedule: several small dusk-to-night feedings. I do 3-5 micro-meals and watch bellies. Slight, even fullness is the goal.
• Enrichment: add HUFA/omega enrichment to live/frozen a few times a week.
• Avoid: big chunks, dry pellets, and bright feeding times. They often ignore static food in bright light.

How they behave and who they get along with

Quiet, schooling, and easily startled. They sit midwater, orient to the current, and pulse forward to grab passing specks. A lone fish tends to sulk and stop eating; a small group settles much better.

• Group size: 6+ is ideal if you can source them. Three is the bare minimum I would try.
• Tankmates: best as a species-only project. Fast swimmers, bright lights, or boisterous feeders will stress them and outcompete them.
• Activity: mostly crepuscular to nocturnal in captivity. Expect very low daytime movement if the room is bright.

Breeding tips

Realistically, this is one for public aquariums with specialized plankton systems. Bigeye lightfish are pelagic spawners with tiny drifting eggs and larvae. I have not seen or heard of a confirmed home spawning, and you would need live marine plankton at multiple sizes around the clock to raise fry.

Common problems to watch for

• Refusal to eat: usually lighting or flow is wrong. Darken the tank, switch to moving live foods, and feed at dusk.
• Panic injuries: nose rubs and scale loss happen after sudden light or vibration. Keep the room calm, pad the lid, and use rounded corners or a kreisel.
• Barotrauma from collection: some arrive with buoyancy issues. If they cannot hold position and keep floating or sinking, survival is hit-or-miss.
• Heat spikes: anything over ~18 C for long stretches will stress them. Have alarms on the chiller and a backup plan.
• Bacterial infections: abrasion spots can fuzz up fast in warm, dirty water. Keep it cold, keep it clean, and avoid harsh meds. If you treat, use gentle options like short baths of nitrofurazone or a low-dose praziquantel for worms once they are feeding.
• Competition: any tankmate that blasts around at feeding time will starve them out. Feed them first, with the room dim, and scatter food into the current.