The study objected to evaluate Litopenaeus vannamei (Boone, 1931) shrimp and Mugil platanus (Günther, 1880) mullet performance in monoculture and polyculture system. Culture of organisms was conducted in earthen ponds at Continental Aquaculture Laboratory of Rio Grande University. The ponds, with approximately 200 m², were early treated with lime and organic fertilization. The treatment were: shrimp monoculture (CM); shrimp and mullet polyculture (P); and mullet monoculture (TM), with three replicates. Shrimp post-larvae (PL) was stocked at a rate of 10 PL m-2 with mean initial weight of 0,02 g (± 0,003 g) and mullets were stocked at rate of 0,67 fish m-2, weighing 1,67g (± 0,32 g). The organisms have been fed with commercial meal to shrimp (38%PB) once a day at evening. Meal rate initially given to shrimp was 20% total biomass, it decreased until 5%, at the end of experiment. To mullets, it was given the same rate throughout experiment (5%). The water quality parameters were measured daily. Experiment had duration of 79 days in summer, from December, 5th, 2007 until February, 22th, 2008. Four biometry was done (at days 0, 30, 60 and 79) to accompany animals weight. At end experiment, gain weight, specific growth rate, feed conversion apparent rate, survival rate and yield of organisms cultured were analyzed. To mullets was analyzed too factor condition. Shrimp showed weight gain, specific growth, feed conversion apparent rate, survival rate and yield on monoculture significantly higher than on polyculture (p < 0,05). Mullet showed weight gain and specific growth rate significantly higher on polyculture (p < 0,05), while its condition factor was significantly higher (p < 0,05) on monoculture. There was no significant difference (p > 0,05) between feed conversion apparent rate of mullets among treatments. The water quality parameters had not significantly different between treatments, excepting transparency witch was biggest to mullet’s monoculture. The shrimp’s performance was suppressed in present mullets; it showed better zootechnic performance in monoculture
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