Choosing Fish for Mixed-Reef Aquariums | How to Select Marine Fish That Can Coexist with Corals and Important Considerations

What is a Mixed-Reef? A Tank Style Where Corals and Fish Coexist

A "mixed-reef" is a style of keeping various corals—including SPS, LPS, and soft corals—alongside saltwater fish in the same tank. A tank where the sculpted beauty and vibrant colors of corals blend with the three-dimensional movement of fish captures the very essence of saltwater aquarium keeping.

However, mixed-reefs have one fundamental prerequisite: choosing the wrong fish risks complete destruction of your corals from predation and stress. Unlike coral-only tanks where water quality alone suffices, mixed-reefs introduce the variable of "compatibility between organisms." This article provides detailed guidance on the criteria for choosing fish that won't fail, along with practical compatibility examples.

Characteristics of Reef-Safe Fish and How to Evaluate Them

"Reef-safe" refers to fish that don't eat corals, peck at them, or cause excessive stress. However, this is merely a trend by species, and individual variation always exists. Reports of reef-safe species still pecking at corals depending on the individual are not uncommon.

When evaluating reef-safety, it's important to consider these three perspectives:

① Diet: Fish that primarily feed on coral polyps or mucus are ruled out. Plankton-eaters, algae-eaters, and carnivores (crustacean-eaters) are generally safe.

② Mouth Shape and Size: Butterflyfish with their tweezers-like narrow mouths are structured to easily nip at polyps. Conversely, gobies and clownfish with smaller, rounder mouths are less likely to damage corals.

③ Individual Temperament: Even within the same species, specimens raised from juveniles may be safe while wild-caught individuals might peck. Close observation during the initial introduction period is essential.

Recommended Fish Species: Mixed-Reef Classics

Clownfish (Nemo Species)

Ocellaris clownfish, pink skunk clownfish, and black ocellaris are the most reliable fish for mixed-reefs. While they're territorial and will chase conspecifics and closely related species, they virtually never eat corals themselves. Introducing a pair and placing an anemone allows you to observe spawning behavior. Note that anemones can harm LPS corals if they come into contact, so careful layout planning is necessary.