Black Piranha

Adults can reach 40–45 cm in length. Sexual dimorphism is weak, and it is difficult to distinguish males from females by appearance. The body is robust and massive, diamond-shaped. Coloration varies depending on the fish's origin: specimens from dark, brownish waters are nearly black, while those from murky waters are grey. The characteristic feature of this species is red eyes.

This species is widely distributed across a large area of South America. Its range includes Venezuela, Guyana, Surinam, French Guiana, Colombia, Ecuador, Peru, Bolivia and Brazil. However, biologists continue to dispute its true boundaries. The fish prefers large river systems, mainly in deep water with fast flow. Young fish usually inhabit calmer, plant-rich waters.

It is a common misconception that piranhas live in schools. In fact, this species is solitary and fiercely territorial. If kept together, the weakest individual may be killed. They gather only during feeding, when hunting large prey. Despite their predatory nature, it is possible to find compatible tank mates: large, well-armoured catfish with defensive spines are suitable.

It is best to leave tank setup and maintenance to professionals. Even with sufficient resources, a beginner may find it difficult to keep such a large predatory fish, which also produces much waste due to its diet. The minimum tank volume for one fish is 500 litres. The décor should include sandy substrate and several pieces of driftwood for shelter. Live plants are tolerated but often uprooted, so artificial plants are a good alternative. Maintaining high water quality requires a powerful filtration system and regular removal of organic waste. A water change of about 50% is essential. There are many nuances to keeping the Black Piranha, but this article does not cover them in detail, since this fish is not suited to the hobby.

These fish eat both live and dead prey. In the wild, Black Piranha schools often attack wounded fish and animals. In an aquarium, diet depends on the fish's history. Recently caught specimens are finicky; their diet should match nature as closely as possible. Acclimated fish accept live or frozen foods such as pieces of mussels, shrimp, squid, and other fish. Young fish can be offered earthworms, insects and small crustaceans. Feed 2–3 times a week. Periodically imitate fasting periods by limiting food. Never feed mammal or bird meat: the fish cannot digest the lipids, leading to fat deposits and even organ degeneration.

Breeding was first achieved in the 1970s at Duisburg Zoo (Germany). Successful breeding in captive conditions is rare. Commercial fish farms are now the main source of fry.

Thanks to their diet, these fish have excellent immune systems. Health problems arise only from poor keeping conditions.

When choosing a Black Piranha, bear in mind that it is a large, territorial predator with specific care requirements. A healthy specimen should be active and free of visible scale damage, ulcers, or fungal infections. Pay attention to the fish's behaviour in the tank: it should not appear apathetic or constantly hide, though shyness is natural for this species. Eyes should be clear, without cloudiness. Be aware of the risk of misidentification when buying, as young fish are often confused with other piranha species. In young Serrasalmus rhombeus, the characteristic red eye colour only becomes apparent at about 12–15 cm. Ask the seller about the fish's origin, as water parameters for comfortable adaptation may differ significantly depending on the collection region. Avoid fish with deformed fins or signs of emaciation, as recovery in home conditions is difficult.