Molly

Mollies have been a staple of the hobby for decades, and for good reason. Native to coastal streams and estuaries from Mexico down through Central America, they've adapted to an unusually wide range of water conditions, including brackish environments that would stress most other community fish. That tolerance makes them forgiving for beginners, though they do have a clear preference for hard, alkaline water. Soft or acidic tanks tend to shorten their lives and make them prone to disease.

Common variants include the classic Black Molly, the speckled Dalmatian, the shimmery Gold Dust, and the short-bodied Balloon Molly. The Sailfin Molly, technically Poecilia latipinna, is a closely related species often sold under the same name, and males grow noticeably larger. Males are easy to tell apart from females by their gonopodium, a modified anal fin used for internal fertilization. Females can store sperm and drop fry every month or so without a male present.

Diet-wise, mollies lean more herbivorous than most community fish. They'll graze algae off glass and decorations constantly, and benefit from regular offerings of spirulina flake, blanched vegetables, or algae wafers. They accept standard flake and pellets readily but do best with plant matter making up a significant portion of their meals.

Temperament is generally peaceful, but males can get pushy, especially toward each other or toward persistently harassed females. A well-structured tank with live plants and some hardscape breaks up sightlines and keeps tension low. Seeing how other hobbyists arrange molly tanks is a great way to get ideas before you set one up yourself.