Chocolate Tetra

Adults reach 3 cm. Males and females look similar; sexual dimorphism is weak. The body is marked by a broad black stripe running from the head to the tail along the midline, dividing the darker yellow back from the silvery belly. The fins sometimes show red pigmentation.

This fish occurs in South America in the upper Tapajós basin. The Tapajós is a right-bank tributary of the Amazon, rising in the Brazilian states of Amazonas and Mato Grosso. The chocolate tetra favours small streams running through tropical forest. These waters have sandy substrates with abundant wood.

The chocolate tetra is peaceful and schooling. Keep it in a group of at least 8–10 individuals. With fewer fish it becomes overly shy, especially if larger species are nearby. It is compatible with other non-aggressive freshwater fish of similar size.

A group of 8–10 needs a minimum tank of 54 litres. Tank design is not critical and depends on your taste. However, the chocolate tetra looks best in a setup that mimics its natural habitat: dim lighting, dense aquatic plants, and wood. Dried leaves of certain trees placed on the substrate make a good addition. Like leaves in natural rivers, these gradually decompose and release tannins, making the water chemistry similar to the fish's home waters. The leaves also form a base for microbial colonies such as Paramecium, which provide valuable live food for fry. Long-term success depends on several factors, with water quality being key. These fish need stable conditions, so avoid sharp swings in water chemistry or temperature, and prevent dangerous levels of ammonia, nitrite and nitrate. The balance of the tank ecosystem depends on adequate equipment—mainly efficient filtration—and regular maintenance. Maintenance means a weekly partial water change, checking water parameters, removing organic waste (uneaten food, droppings) and replacing leaves if you use them.

Feeding poses no difficulty. In the home tank they readily eat most common foods: flakes and granules are fine as a daily diet. You can vary their food with live or frozen items such as Artemia or Daphnia if you wish.

Breeding follows the pattern typical of characins. Females scatter eggs among plants or on the open substrate; males then fertilize them. There is no fixed breeding season; different fish breed at different times. These fish show no parental care, so the eggs will usually be eaten. To preserve the brood, transfer the fertilized eggs to a separate tank with water identical to the main tank. Otherwise they will be consumed.

No diseases are known to strike this species alone. Given suitable conditions—clean water, a balanced diet and peaceful tank mates—health problems are rare. Poor conditions are the usual cause of illness; they weaken immunity and leave the fish open to infections always present in the tank. If you notice early signs of illness—lethargy, weight loss, refusing food or clamped fins—first check your water parameters. Often good conditions restore health on their own. If the fish is too weak or has visible damage, medicine may be needed.

When buying, look for active fish with intact skin. Healthy ones school together, show curiosity and respond eagerly to food. Avoid thin fish, those with torn fins or unnatural coating on the body. Bear in mind that stress in the shop makes colours pale, but the fish should not seem apathetic or hide in corners. Buy a group of at least 8–10 individuals: this species suffers severe stress if kept alone.