Dwarf herring

Where they come from

Dwarf herring are tiny, silvery schooling fish from the tropical western Atlantic and Caribbean. Think mangrove edges, seagrass beds, and the calm side of reefs. You see them flashing at the surface at dawn and dusk, grabbing zooplankton and dodging everything that wants to eat them.

Setting up their tank

They look small, but treat them like open-water fish. A long tank with room to loop the perimeter keeps the school tight and calm. I would not try fewer than 10-12; 15-20 is better. They relax in numbers.

• Tank size: 75 gallons is a workable minimum for a group; bigger is kinder if you want a larger school.
• Salinity 1.024-1.026, temp 76-80 F, pH 8.0-8.4. Keep oxygen high with strong surface agitation.
• Flow: steady, laminar flow helps them cruise. A gyre pump on low-to-medium works well.
• Lighting: diffuse and not too punchy. Sudden on/off spooks them. Use a ramp timer.
• Cover: tight-fitting lid with 1/8 inch mesh or finer. Seal every gap. They launch like rockets.
• Scape: open water up front and along the top, with darker background or side panels to cut reflections.
• Filtration: strong skimming and decent mechanical filtration. You will feed often, so plan for nutrient export.
• UV sterilizer: helpful for planktonic parasites and water clarity. Shoot for slow-to-medium contact time.

Quarantine them as a group in a dim, quiet tank with the same flow and lid setup. They pile into corners if they feel exposed, so give them a dark back and sides and keep activity low around the tank for the first week.

What to feed them

They are plankton pickers with tiny mouths. Start with moving, bite-size foods and lots of them. Once they recognize the feeding zone, you can mix in frozen and then small dry foods.

• Live foods that get them started: enriched baby brine shrimp, copepods (Apocyclops, Tigriopus), and small mysid nauplii.
• Frozen they accept: cyclops, Calanus, fish or prawn eggs (R.O.E., ova), finely minced seafood slurries. Regular mysis is usually too big.
• Dry food options: 0.3-0.8 mm micro-pellets (TDO A/B, Otohime) once they are confident. Soak and release into the flow so it stays suspended.
• Feeding rhythm: 3-5 small feedings per day beats one big dump. I use a feeding ring in front of a gentle gyre so food drifts past the school.

How they behave and who they get along with

They are classic schooling fish: tight group, constant motion, easily startled. In a settled tank they cruise mid-to-upper water and flash like a living mirror. If the group is too small, they get jumpy and go off food.

• Good tankmates: peaceful reef fish that ignore them - chromis, cardinals, dartfish, smaller fairy/flasher wrasses, tiny gobies, assessors. Corals and inverts are fine.
• Use caution: hyper or territorial fish (clownfish guarding a nest, boisterous tangs) can scatter the school.
• Avoid: any predator with a big mouth - lionfish, groupers, hawkfish, larger wrasses, dottybacks, and hungry anthias that outcompete them. Seahorse tanks are a bad match due to flow and feeding style.

Breeding tips

They are broadcast spawners. Healthy, well-fed groups often do dusk chases and release eggs into the water column. The eggs and larvae are tiny and get skimmed or eaten almost immediately.

If you want to experiment, pull a fine filter sock from the overflow right after lights out and check for clear, buoyant eggs. A round kreisel-style larval tub, gentle air, greenwater, and a steady supply of copepod nauplii would be the path. It is a project for dedicated larval-rearing folks, not a casual attempt.

Common problems to watch for

• Shipping shock and ammonia burn: look for rapid breathing, red gills, or listlessness. Give them max oxygen and low stress the first 48 hours.
• Starvation: pinched bellies and restless surface picking mean the menu is wrong or too infrequent. Increase feeding frequency and particle variety.
• Parasites: flashing and gulping can be gill flukes; thin, white stringy feces points to internal flagellates or worms.
• Spooking and pile-ups: bright point lights, sudden room movement, or mirrored ends cause crashes into glass. Diffuse light and add a dark background.
• Medication sensitivity: they do not love harsh treatments. Copper and formalin can go sideways fast if oxygen is low.

Expect a shorter lifespan compared to many reef fish; these are fast-living, schooling planktivores. If you keep the group size up, feed small and often, and give them safe open water, they reward you with constant motion and that glittering school effect that makes a reef feel alive.