Macrobrachium carcinus is a species of freshwater shrimp native to streams, rivers and creeks from Florida to southern Brazil. It is the largest known species of Neotropical freshwater prawn, growing up to 30 centimetres (12 in) long and weighing as much as 850 grams (30 oz), although even larger specimens have been reported. It is an important species for commercial fishing in the Sao Francisco area, where it is known by the local name of pitu. M. carcinus is omnivorous, with a diet consisting of molluscs, small fish, algae, leaf litter and insects.