Fusiliers

One species, listed in all three tiers: the Yellowback Fusilier. Fusiliers are open-water plankton feeders built like tuna in miniature — they swim constantly, in a group, and they do it in a straight line. This is a fish for a long tank with a lot of open swimming room and very little rockwork in the middle.

Be honest about your footprint before you buy. In a standard six-foot-or-shorter reef they pace the glass and wear themselves down, and a single one kept alone rarely settles. If your tank is deep front-to-back rather than long, a smaller schooling Chromis or anthias does the same job better. Open-water fish also ship badly, so the quarantined tier is the safer buy here.