Brazilian Chromis

Where they come from

Brazilian Chromis hang out over reefs along Brazil's coast in the South Atlantic. In the wild you see loose groups holding in the current above rock and coral, nabbing passing plankton and ducking back to cover if something spooks them.

They are classic midwater damselfish. Think open water to roam, plus rock gaps to reset the pecking order.

Setting up their tank

For a single fish, a 30-40 gallon tank works. If you want a group (which looks great), aim for 55+ gallons so they have room to spread out. Give them open swimming space in the middle and plenty of rock with caves and ledges for line-of-sight breaks.

• Temperature: 75-79 F (24-26 C)
• Salinity: 1.024-1.026
• pH: 8.1-8.4, alkalinity 8-12 dKH
• Zero ammonia and nitrite; nitrate under 20 ppm
• Flow: moderate to strong, with a calmer area to rest
• Lighting: anything from moderate reef lighting to standard marine lighting is fine

Run a tight-fitting lid. Chromis are not chronic jumpers, but a chase at lights-out can send one airborne. They settle best in mature tanks with stable parameters.

What to feed them

They are plankton pickers, so think small, meaty foods. Feed 2-3 small meals a day if you can. They learn pellets and flakes quickly, but a mix keeps them in good shape.

• Quality marine pellets (small size) and flakes
• Frozen mysis and enriched brine shrimp
• Frozen cyclops, calanus, or finely chopped seafood
• Copepods (live or frozen) for new or picky fish
• Occasional nori scraps are fine, but they are mostly carnivorous

How they behave and who they get along with

Generally peaceful, active in the midwater, and fun to watch at feeding time. Like most damselfish, they sort out a pecking order. In tight quarters or with too few hiding spots, the dominant fish may keep chasing the weakest one.

• Good tankmates: clownfish, gobies, blennies, fairy/flashers wrasses, royal grammas, firefish, tangs, reef-safe dwarf angels, cleaner shrimp
• Use caution with: very bold dottybacks, large hawkfish, and pushy damsels that may harass them
• Avoid: large predators that see small schooling fish as snacks

Breeding tips

They are nest spawners. A male will clean a patch of hard surface, the female lays a clutch, and the male guards and fans the eggs. You might see this in a peaceful, well-fed tank, but raising the larvae is the hard part.

• Use a separate 20-30 gallon bare-bottom tank with a few tiles or small clay pots for nesting.
• Stable, clean water and frequent small feedings condition the pair.
• Eggs hatch in a few days; larvae are tiny and go pelagic.
• You will need rotifers, greenwater (phytoplankton), then baby brine/copepods as they grow.
• Keep light gentle and flow mild for the first weeks.

Common problems to watch for

Chromis in general sometimes come in with Uronema, a nasty protozoan. Signs are tiny red sores, frayed scales, and a fish that eats one day and crashes the next. This is one reason I quarantine new chromis.

• Uronema and other parasites: Quarantine new fish 4 weeks. Observe closely. Copper treats ich/velvet; Uronema needs different meds, so get an ID before treating.
• Group attrition: If one fish is always hiding with a torn tail, the hierarchy is too tight. Add cover, spread feeding out, or rehome the bully.
• Jumping during scuffles: Use a lid and dim the lights before lights-out to cut startle jumps.
• Hollow bellies: Feed smaller meals more often and include some higher-protein options like mysis and calanus.