Assorted Betta (Betta splendens)

Bettas get labeled a beginner fish and a solitary fish in the same breath, and both reputations are a little misleading — they're a labyrinth fish that can breathe surface air (genuinely low-maintenance on the oxygen front), but they're also intelligent, food-motivated, and considerably more interactive than people expect from something sold in a cup. Males build bubble nests at the surface as part of their natural breeding behavior even with no female present, a floating cluster of mucus-coated bubbles that's completely normal and a good sign of a healthy, content fish. Famously intolerant of other male Bettas and often other long-finned fish, but plenty of quiet, fin-safe community tankmates work fine alongside one.