Blackline penguinfish

Thayeria boehlkei, known as the Blackline Penguinfish or False Penguin Tetra, is a peaceful schooling characin from the upper Amazon basin in Peru and the Rio Araguaia in Brazil. It reaches a length of at least 6 cm, with large specimens attaining 7.5 cm, and is named for the distinctive black line running along its lower flank. A group of 6–10 individuals requires a tank with a base of at least 60 × 37.5 cm, ideally larger for maximum comfort. Water conditions are highly adaptable: temperature 22–28 °C, pH 5.5–8.0, with hardness up to 20 °H, reflecting the fact that almost all fish in the trade are mass-produced from captive-bred stock. The species makes a superb addition to the well-planted aquarium with a dark substrate, driftwood, and floating plants to provide shady conditions. A micropredator by nature, it feeds on insects, worms, crustaceans, and other small invertebrates in the wild. In the aquarium it is unfussy and greedily accepts dried flakes and granules, but should be offered regular meals of live and frozen foods such as bloodworm, Daphnia, and Artemia for optimal health and colouration. Peaceful and schooling, it should never be kept in groups smaller than six. Fin-nipping behaviour occasionally attributed to this species is usually absent when kept in sufficient numbers. Suitable tankmates include Hemigrammus and Hyphessobrycon tetras, pencil fish, Apistogramma dwarf cichlids, Corydoras, and small Loricariids. Females are more rounded in the belly and slightly less intensely coloured than males.