A pacu is a freshwater fish belonging to the Serrasalmidae family, native to South America. It is an omnivorous fish, consuming both plant and animal matter. Pacu are related to piranhas but exhibit distinct characteristics and behaviors. These fish are found predominantly in tropical and subtropical regions.
Distinguishing Features
Pacu can grow to a substantial size, with some species reaching lengths of up to 3 feet (0.9 meters) and weighing over 88 pounds (40 kg) in the wild. They possess broad, flattened bodies that can appear in various neutral colors like silver, gray, black, or white, though some species, like the red-bellied pacu, display brighter hues when young. A defining feature of the pacu is its dentition, which consists of square, flat teeth that resemble human molars.
These teeth are adapted for crushing and grinding hard plant materials such as nuts and seeds. This dental structure contrasts sharply with that of piranhas, which have pointed, razor-sharp, triangular teeth designed for tearing flesh. While both pacu and piranhas share similar body shapes, their jaw alignment and tooth structure differentiate them, reflecting their differing diets. Piranhas have a pronounced underbite, whereas pacu exhibit squarer, straighter teeth and a less severe underbite or a slight overbite.
Natural Environment and Behavior
Pacu are native to the freshwater systems of tropical and subtropical South America, primarily inhabiting the Amazon and Orinoco river basins. They thrive in various freshwater environments, including rivers, lakes, floodplains, and flooded forests. Their habitat preferences can vary among species, with some exhibiting migratory behaviors.
In their natural environments, pacu are primarily omnivorous, preferring plant matter. Their diet largely consists of fruits, nuts, seeds, and aquatic vegetation that fall into the water from overhanging trees. They may also occasionally consume small invertebrates or fish, especially when preferred plant-based food sources are scarce. Pacu are shy and docile fish in the wild, exhibiting non-aggressive behavior unlike their piranha relatives.
Pacu in Captivity and Beyond
Pacu are frequently sold as small, attractive fish in the aquarium trade due to their initial appearance. However, they grow rapidly and can quickly outgrow typical home aquariums, often reaching lengths of 12 to 24 inches even in captivity. This rapid growth and large adult size often lead to owners releasing these fish into local waterways when they can no longer accommodate them.
The release of pacu into non-native aquatic environments poses ecological concerns, as they can become invasive species. These introduced pacu can disrupt local ecosystems by competing with native species for food resources and habitat. Their presence can also alter the natural balance of an ecosystem, leading to declines in native fish populations. In many regions, releasing non-native species into public waters is illegal due to the potential for environmental damage.