Cachama

About

Cachama (Colossoma macropomum), also known as blackfin pacu or tambaqui across its native range, is the second-largest scaled fish in the entire Amazon basin. And that fact alone tells you most of what you need to know about keeping one. Adults can push well past three feet in length, and the notion that fish grow only as large as their tank allows is a persistent myth that has led to countless specimens being abandoned at public aquariums or, worse, released into local waterways. In the wild, this species inhabits the flooded forests of the Amazon and Orinoco basins, where adults spend months gorging on fallen fruits, nuts, and seeds. Their teeth are genuinely remarkable. Cusped, molar-like structures capable of crushing hard seeds, and backed by powerful jaws that can deliver a serious bite during tank maintenance if you're not careful. Temperament-wise, cachama is broadly peaceful with similarly-sized fish, though its constant movement can stress shy or sedentary tankmates. Juveniles are social and can be kept in groups, but adults trend toward solitary behavior and may harass their own kind in cramped conditions. Suitable companions include arapaima relatives, large cichlids, and big catfish from the pimelodid and loricariid families. This is genuinely a species for dedicated, experienced keepers with the space to do it properly.