On the top is a fish known as the Payara and/or the Pirandira. The scientific name is Hyrdolycus, an awe-inspiring predator with giant fangs on their lower jaws. They use those sharp fangs to stab their victims from below. They grow to the size of king salmon and are tremendous fighting sport fish.
Below that is a toothy little fellow known as a freshwater Barracuda ( Acestrorhynchus falcatus).
On the lower right is another armored catfish with razor sharp rows of knife-like scales, known as a Ripsaw Catfish (Oxydoras niger).