Penguin tetra, blackline penguinfish (Thayeria boehlkei) care guide

Group
Freshwater fish
Other names
Hockeystick tetra, Blackline penguinfish, False penguin tetra, Blackline thayeria, Penguin fish
Family
Acestrorhamphidae (American tetras; formerly Characidae)
Origin
Probably restricted to parts of the upper Amazon basin in Peru and the Rio Araguaia in Brazil.
Water
freshwater
Maximum size
3.6 cm
Temperature
22–28°C
pH
5.5–8
Hardness
Very soft to hard, 0–20 dGH
Minimum tank
70 litres
Care level
beginner
Temperament
peaceful

Care

The penguin tetra is named for its distinctive head-up resting posture and the bold black line that runs along the body and down into the lower tail lobe. It is a peaceful shoaler and should always be bought as a group of at least six, preferably ten or more; it tends to hang in the upper half of the tank. A tank with a base of at least 60 × 38 cm suits a group. It does well in a planted community tank or a jungle-style set-up with driftwood, leaf litter and fairly dim lighting. It is very adaptable regarding water chemistry: anything from very soft to hard water (up to around 20 dGH), a pH of roughly 5.5–8.0 and temperatures of 22–28 °C. Almost all the fish in the trade are mass-produced on farms, so they are robust and easy to keep with regular partial water changes. Spawning pairs scatter up to 1,000 sticky eggs among plants; they hatch in about 20 hours and the fry swim freely after four days. Sources: Seriously Fish (seriouslyfish.com/species/thayeria-boehlkei/); FishBase (fishbase.se/summary/Thayeria-boehlkei.html); Wikipedia (en.wikipedia.org/wiki/Thayeriaboehlkei). Checked October 2026.

Diet

A micropredator of small invertebrates in nature. In the aquarium it takes dried flakes readily, but feed small live and frozen foods such as bloodworm, daphnia and brine shrimp regularly to keep it in top condition.

Breeding

Quite easily bred in a separate tank. Adult females are rounder in the belly and slightly less intensely coloured than males. Condition a group or pair on live and frozen foods and spawn them in soft, slightly acidic water with fine-leaved plants or mesh over the base. It is a prolific egg-scatterer – a female can produce around 1000 eggs – and the adults will eat them, so remove them after spawning. The fry are free-swimming within 3–4 days; start them on infusoria-type foods, then brine shrimp nauplii.

Compatibility and tank mates

Peaceful and a good community fish. Works well with other South American tetras, pencilfish, small catfish such as Corydoras, dwarf cichlids and other peaceful community fish of similar size. Avoid large or predatory species.

Last updated 4 October 2026. Community-edited care guide on Aquatic-Auctions.

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