Black Pacu

The first thing that invariably catches the eye when observing a Black Pacu is its colossal size. In a home aquarium, the fish often grows to over 70 cm, and its high, laterally compressed body makes its appearance truly imposing. It is important not to confuse this species with the Red-bellied Pacu, its closest relative, which is distinguished by its reddish belly coloration and more modest dimensions, not exceeding 50 cm. The coloration of the Black Pacu can vary from gray to rich black tones, with the fins always being dark.

The Black Pacu was first described by the researcher Cuvier in 1816, when he was studying the fauna of the Amazon and Orinoco river basins, located in South America. Nowadays, these fish are found in almost all major rivers of the tropical zone of the New World. Since the mid-90s of the last century, they can also be found in Asia, where they are actively bred as a food source. In their natural habitat, the fish prefer to stay alone, inhabiting the dark waters of flooded forests. Their diet is very diverse and consists of everything that can fit into their mouths: this includes fruits, grains, as well as insects and plant debris. Sometimes they are not averse to feasting on small fish.

This fish prefers proud solitude, but at the same time, it will not refuse the company of other species if they meet certain conditions: they must be peaceful, non-aggressive, non-territorial, and large enough not to accidentally become part of its diet.

The main difficulty in keeping Tambaqui is related to the need to acquire a very large aquarium and find a suitable place for its installation, as a fully filled system can weigh about a ton. To maintain high water quality, high-performance filters and regular water changes of 30–50% of the volume every two weeks are necessary. Other equipment is standard and includes a heater, aerator, and lighting fixtures. These fish prefer the middle layers of the water, so when decorating the aquarium, sufficient free swimming space should be provided. Large plants, driftwood, as well as artificial grottoes and shelters can be used as decor. Despite their impressive size, Pacu are timid; sudden noises and vibrations can cause them to panic, which may lead the fish to hit the aquarium walls.

In an aquarium environment, these fish exhibit an excellent appetite, consuming almost all types of food. They readily eat dry commercial foods, such as large pellets and tablets, as well as plant components and meat, including frozen. An approximate diet may include chopped pieces of apple, zucchini, or other vegetables and fruits, mixed with meat products, such as shrimp or mollusks.

Due to their impressive size, Black Pacu are not bred in home aquariums; this requires specialized nurseries located in natural backwaters. Nevertheless, attempts have been made to breed this species, mainly for research purposes. The first successful experiments to obtain offspring in captivity date back to 1992, when healthy offspring of these giants were obtained using hormonal stimulation at a research center in Natal, Brazil.

As with any large fish, insufficient space and nutrient deficiency can be common problems for Pacu, which often negatively affects their well-being. Otherwise, this species is highly resilient. More detailed information on the symptoms of possible diseases and methods of treatment is presented in the section “Diseases of Aquarium Fish.”

When purchasing a black pacu, it's important to consider that it is a large fish, often mistakenly sold as a piranha due to its external resemblance when young. Healthy specimens should be active, have clean fins without signs of damage, coatings, or ulcers, and exhibit even breathing. Avoid fish with sunken bellies, cloudy eyes, or unnatural behavior, such as constantly hovering at the surface. Given their rapid growth and the enormous size of adult specimens, before purchasing, it is essential to ensure that you have the conditions to keep the fish long-term, as most aquariums are not suitable for an adult pacu. Often, specimens with signs of stunting are found in stores due to prolonged keeping in cramped tanks, which can lead to irreversible health problems.