The blackline penguinfish is also called Boehlke’s penguinfish, false penguin tetra and hockey sticks. This species needs at least a 20-gallon aquarium for a small group of six or more fish. This fish is hardy and sticks to the upper waters of the community aquarium. Instead of swimming horizontally like most aquarium fish, the blackline penguinfish swims with its head slightly raised. The body is mostly an olive color, but its characteristic thick black stripe begins just behind its gill cover and extends all the way to the bottom lobe of its forked caudal fin. If the light reflects well, a thin greenish-gold line can be seen just below the black stripe. The fins are colorless. The blackline penguinfish is sometimes confused with Thayeria obliqua, which looks similar, but the black line on Thayeria obliqua begins after the dorsal fin (on Thayeria boehlkei, the line begins just behind the gill cover).
The blackline penguinfish should be kept in a well-planted aquarium with dark substrate. Floating plants can also provide shady hiding places for this species.
Feed your blackline penguinfish flake foods and small live foods, including worms, crustaceans and insects.
Breeding: Females have a much rounder belly, especially when filled with roe. The breeding aquarium should be dimly lit and include a slowly bubbling sponge filter, as well as clumps of fine-leaved plants or spawning mops. The water needs to be soft and slightly acidic, and it should be several degrees warmer than the breeders’ display aquarium. A group of these fish can spawn at the same time in the same breeding aquarium. Place the breeders into the aquarium at night, and they should spawn in the morning, with each pair laying and fertilizing about 1,000 eggs. After they have completed the breeding attempt, remove the parents to prevent them from eating the eggs. A water change may also need to be made due to the large amount of sperm that the males release into the water. Eggs hatch in about 24 hours. The fry are free-swimming in about four or five days. Feed blackline penguinfish fry newly hatched brine shrimp, infusoria, Daphnia, finely crushed flake food and other small foods.