Danionella cerebrum Care Guide - Tank Setup, Diet & Breeding

Danionella cerebrum is one of the world’s smallest known fish and is often called the brain fish because its unusually transparent body allows the brain and internal structures to be seen in living specimens. Its body is slender, delicate and lightly pigmented, with a small mouth and subtle golden, silvery or reddish details that become more noticeable under aquarium lighting.

This species is a danionin relative of the familiar danios, but it is far smaller and more specialised in appearance. It is an active, social fish that spends much of its time in the midwater and upper areas of the aquarium, where a group can produce a fascinating display of tiny, constantly moving bodies.

Danionella cerebrum is notable not only for its size but also for its complex acoustic communication. Males can produce audible clicking or drumming-like sounds using specialised structures associated with the swim bladder, an unusual ability among such small vertebrates.

In the wild, it is associated with quiet, sheltered freshwater environments containing fine vegetation, leaf litter and subdued light. Its transparent form and shy demeanour make it best appreciated in a calm aquarium with plenty of cover rather than alongside large or highly competitive fish.

Danionella cerebrum is native to freshwater habitats in Myanmar, in Southeast Asia. It comes from small, shallow streams and pools associated with the Myanmar river systems, where it inhabits sheltered, slow-moving margins.

A group should be given at least 20 litres, with a footprint of around 45 by 30 cm preferred over a tall aquarium. Use a mature, stable setup with gentle filtration, subdued lighting and a secure cover, as these delicate fish may jump when startled. A dark fine-grained substrate, Java moss or other fine plants, floating plants, leaf litter and small pieces of smooth wood provide shelter and help the fish feel secure. Leave some open water for shoaling, and use an air-powered sponge filter or guard the intake carefully so the fish cannot be drawn in. Keep the water around 22–26°C, with a pH of approximately 6.5–7.5 and low to moderate hardness.

Up to approximately 1.5 cm (0.6 in) in adult length. Females are generally slightly larger and fuller-bodied than males, while males remain more slender.

This tiny micropredator needs very small foods, including live or frozen baby brine shrimp, microworms, grindal worm fragments, cyclops, daphnia and suitable fine powdered foods. Newly hatched brine shrimp and cultured infusoria are particularly useful for young fish. Offer small portions several times a day, ensuring that food particles are small enough for the fish to eat without prolonged competition from tankmates.

Danionella cerebrum is best kept in a species-only aquarium or with other exceptionally peaceful nano fish of similar size. Suitable companions may include small groups of least rasboras, celestial pearl danios or other tiny, non-predatory danionins, provided the aquarium is spacious and competition for food is limited. Avoid larger danios, barbs, tetras, gouramis, cichlids, bettas, loaches and most catfish, as even peaceful fish may swallow or outcompete this minute species.

Danionella cerebrum is an egg-scattering species that can breed in a mature, well-planted aquarium. Condition a group with plentiful small live or frozen foods, then provide fine-leaved plants, moss or a spawning mop for the eggs to fall into. Adults may eat the eggs and fry, so move the spawning material or use a separate breeding tank. The tiny larvae require infusoria or another suitably small first food before they can accept newly hatched brine shrimp and other miniature foods.

Females are usually a little larger, deeper-bodied and more rounded through the abdomen, particularly when carrying eggs. Males tend to be smaller and slimmer, with more subtle differences that can be difficult to judge in such a minute, transparent fish.