Combining reef fish: which fish go together?

Reef safe or not, peaceful or territorial, and in what order do you add them? How to put together a fish population that lives calmly alongside your corals and invertebrates.

Royal gramma, purple and yellow, between corals
Photo: H. Zell, CC BY-SA 3.0, via Wikimedia Commons

In a reef aquarium, fish not only have to get along with each other, but also with corals, shrimp and snails. A well-considered choice prevents fights and disappointments.

Reef safe or not?

A fish is called reef safe if it leaves corals and invertebrates alone. That is a general rule, not a guarantee: individual fish can differ.

  • Usually reef safe: clownfish, gobies, royal gramma, cardinalfish, most tangs and many wrasses.
  • With caution: dwarf angelfish (sometimes nibble on corals), some wrasses and hawkfish (may eat shrimp).
  • Not reef safe: most large angelfish, triggerfish, pufferfish and butterflyfish that eat coral polyps.

Peaceful or territorial?

Many reef fish defend a territory against their own kind and against species of similar shape or colour. So usually keep one individual per species, except for species that live in pairs or groups, such as clownfish (as a pair) and cardinalfish. Tangs of the same genus often tolerate each other poorly.

The right order

  1. First the most peaceful and smallest fish, such as gobies and cardinalfish.
  2. Then the somewhat more territorial species, such as a royal gramma or a pair of clownfish.
  3. Last the dominant species, such as a dwarf angelfish or tang.

Whoever is in the aquarium first claims the best spots. By adding the most dominant fish last, you prevent them from chasing away newcomers. Only add one or two fish at a time, so the biological filter can grow along.

How many fish?

A reef aquarium tolerates fewer fish than a freshwater tank, because corals are sensitive to nitrate and phosphate. Take into account each fish’s adult size, swimming behaviour and the amount of food it needs. Fewer fish means more stable water.

Example: a reef aquarium of about 300 litres

  • 2 clownfish (Amphiprion ocellaris), tank-bred
  • 1 royal gramma (Gramma loreto)
  • 1 firefish (Nemateleotris magnifica)
  • 1 shrimp goby with a pistol shrimp (a fascinating partnership)
  • 3 Banggai cardinalfish (Pterapogon kauderni), tank-bred
  • Cleaner shrimp (Lysmata amboinensis) and a clean-up crew of snails and hermit crabs

Quarantine

Keep each new fish in a separate quarantine tank for four to six weeks first. One sick fish can infect the whole aquarium, and in a reef aquarium you can’t use most medications because they kill corals and invertebrates.