Penguin Fish

About

Penguin Fish (Thayeria obliqua) is a small South American characin with a genuinely interesting identity problem: it was the original fish to earn the 'penguin' nickname, but that name has since migrated almost entirely to its close relative, Thayeria boehlkei. The two are easy to separate once you know what to look for. In T. obliqua, the bold black lateral stripe tapers upward and fades out well before reaching the dorsal fin, whereas in boehlkei it runs all the way forward to the gill cover. Both species share the genus's signature swimming posture. A distinctive head-up, angled style that gives the group its common name. Wild fish come from the middle Amazon, middle Tocantins, and Guaporé River drainages of South America. In the aquarium it's a peaceful, undemanding fish that fits well into a community alongside other small South American tetras, pencilfish, Corydoras, and small cichlids like Apistogramma. The key to keeping it well is numbers. A group of at least six is the minimum, with ten or more bringing out the best schooling behavior and reducing any tendency toward fin-nipping. It's a solid beginner species, honest in its needs, and arguably deserves far more shelf space at the fish store than it currently gets.