Litopenaeus vannamei juveniles (5.6 +/- 0.6 g), at an initial density of 152 individuals/m(2), were grown for 28 days in 12 cylindrical 1,000-l tanks with no water exchange. Three tanks had 7.1 m(2) Aquamats (R) to promote periphyton growth, and six had 7.1 m(2) geotextile fabric or mosquito net (three for each substrate). The remaining three served as controls. The shrimp were fed 35% protein shrimp feed, twice daily, supplied on demand. There were no differences in dissolved TAN or unionized ammonia (NH3) concentrations between treatments with substrates, but they were significantly lower than in the control. N-NO3- values were higher in tanks with substrates, possibly indicating faster nitrification rates. These tanks produced shrimp with higher mean individual weights and growth rates than the control, but the final yield in tanks with mosquito netting was intermediate between the control and the remaining treatments. The highest feed and economic feed conversion indices, and the lowest nitrogen utilization and protein efficiency ratio, were in the control, and there were no differences between the three treatments with added substrates, showing that the less expensive geotextile fabric and mosquito net may be used with the same efficiency as Aquamats (R) in periphyton-based aquaculture.