These fish are adult size and fully colored up.  They are healthy and lively.

Penguin tetras (*Thayeria boehlkei*) are a striking and lively addition to any freshwater aquarium, known for their unique, slightly tilted swimming posture and sleek, silver bodies adorned with a bold black stripe that runs from their eye to the tip of their tail. These peaceful, schooling fish thrive in groups of at least six, displaying their best colors and behaviors when kept together. To keep them healthy, maintain a well-planted aquarium with plenty of swimming space and stable water parameters: a temperature range of 72-82°F (22-28°C), a pH of 6.0-7.5, and soft to moderately hard water (2-15 dGH). They are active yet peaceful, making them excellent tankmates for other community fish. Providing a varied diet of high-quality flakes, pellets, and occasional live or frozen foods like brine shrimp and daphnia will keep them vibrant and energetic. With their shimmering scales and graceful, coordinated movements, penguin tetras bring both beauty and dynamic energy to any well-maintained aquarium.