The annual flooding cycle in the Pantanal is the main factor responsible for the huge reproduction of fish in the area. The diversity of aquatic habitats allows the existence of a great number of species, which through the years developed different ways of life and reproduction.

The species that are most important for sport fishing can be found in the areas where greater flooding occurs. The most spectacular natural, ecological phenomenon takes place in these flooded regions of the Pantanal; this is called "Piracema", the up river migration for reproduction of different species. The majority of large sport fish are part of this phenomenon.

There where 263 species of fish recorded in the Pantanal, being that more than 85% belong to the group of Ostariophysis. Some examples of these are as follows: the pacú, the dourado, the tuvira, the pintado and the cascudo.

The great amount of fish found in the Pantanal, represent two of the biggest reserves of live nutrients and energy stock of the system, influencing the circulation of these elements. Fish are highly responsible for carrying around seeds, which are a main source of food for the existing fauna.