The present experiment aimed to evaluate the performance of the shrimp Lithopenaeus vannamei and the mullet Mugil platanus in monoculture and polyculture. The organisms were created in excavated ponds, located at the Continental Aquaculture Laboratory of the Federal University of Rio Grande. The nurseries with an area of ​​approximately 200 m2 were previously treated with quicklime and fertilized with tanned bovine manure. The treatments, in triplicate, were: shrimp monoculture (CM); polyculture of shrimp with mullet (P); and mullet monoculture (TM). The shrimp post-larvae (PL) were stored at a density of 10 PL m-2 with an initial weight of 0.02 g (± 0.003 g) and the mullets at a density of 0.67 fish m-2, initially weighing 1, 67g (± 0.32 g).Fish and shrimp were fed commercial shrimp feed (38% CP) once a day. The amount of feed given to the prawns was initially 20% of the total biomass, decreasing up to 5% at the end of the experiment. The mullets were offered 5% of their biomass throughout the experiment. The physical and chemical parameters of the water were recorded daily. The experiment lasted 79 days during the summer of 2007/2008. Monitoring of animal growth was performed by weekly biometrics. At the end of the experiment, weight gain, specific growth rate, apparent feed conversion, survival and production of cultivated animals were verified, as well as the condition factor for mullets. Monoculture shrimp showed weight gain (15.59g), specific growth rate (8,40% day-1), apparent feed conversion (0.88), survival (91%) and production (1,454 kg ha-1) significantly higher (p <0.05) than in polyculture. Mullets in polyculture showed weight gain (42.72 g) and specific growth rate (3.99) significantly higher (p <0.05) than in monoculture, while their condition factor was significantly (p <0.05 ) lower in polyculture (1.06). The apparent feed conversion of mullets did not show significant differences (p> 0.05) between monocultures (2.50) and polycultures (2.40). The physical and chemical parameters were not significantly different (p> 0.05) between the treatments adopted, with the exception of the transparency, which was higher in a mullet monoculture nursery.