How many should you keep together?
Search any fish to see the minimum group size our compatibility rules apply to it. Keep in mind what this answer is: one constraint out of several. “Keep six or more” is useful, but it is not a compatibility decision on its own.
Uses the same genus- and name-based schooling rules as the AquaLens app's tank compatibility analysis. The minimums are floors, not targets — most shoaling fish look and behave better in 10+.
Plan the whole community
Group size is one input. A real plan also weighs adult size, swimming space, territory, existing residents, filtration, and the routine keeping the system stable.
Why the minimum is a floor, not a target
The numbers here are the point below which a shoaling fish starts showing stress behavior: hiding, faded color, fin nipping directed at tankmates, or refusing to use open water. They are not the number at which the fish is thriving. Most shoaling species look and behave noticeably better at ten or more than at the six you will see quoted everywhere, and the difference is obvious once you have seen both.
That makes the minimum a useful safety check and a poor goal. If a group of six is all your tank can support, the honest read is often that the tank is too small for that species rather than that six is enough.
What a “no group minimum” result does and does not mean
Some fish are on the non-schooling list because they genuinely do better alone or in pairs, and a few, bettas being the obvious case, should not be kept together at all. A result of “no group minimum” means our ruleset has no group-size floor for that species. It is not a statement that the fish is happy in isolation, and it says nothing about whether it will get along with the rest of your list.
A “not covered by our ruleset” result means exactly that. Our rules match on genus and common-name patterns, so an uncommon species can fall through without being any less social. Treat that as missing information rather than as a green light, and check the species page before you buy.
Want the why behind the numbers? Read the stocking & compatibility guide.