High-intensity, zero-exchange shrimp ponds contain a high density of flocculated particles, rich in bacteria and phytoplankton, compared with flow-through systems. The flocculated particles provide a potential food source for shrimp. Short-term tank experiments were conducted to determine the retention of nitrogen (N) from natural biota, dominated by flocculated particles, in white shrimp (Litopenaeus vannamei) at a high-intensity, zero-exchange shrimp farm in Central America (Belize Aquaculture (BAL)). There were two treatments: 'floc' and 'floc+20%' (3ױ000-l replicate tanks each) based on two densities of flocculated particles. The floc density in the 'floc' treatment was typical of shrimp growout ponds at BAL, whereas the 'floc+20%' treatment had a 20% higher density of flocculated particles. Three consecutive experiments were conducted with 1, 5 and 9 g shrimp, respectively. At the start of the experiment, 15N-ammonium was added to the tanks and assimilated by the natural biota. Shrimp were maintained in these tanks for 48 h after the 15N-nitrogen enrichment. After this time, shrimp were found to be enriched with 15N-nitrogen. It was calculated that between 1% and 3% of the particulate nitrogen in the tanks, principally from the flocculated particles, was retained by the shrimp. The proportion of estimated daily nitrogen retention of the shrimp contributed by the natural biota was calculated to be 18% to 29% for 1 to 9 g animals in the floc treatment. There was a tendency for greater retention in the floc+20% treatments, but this trend was not consistent. This study suggests that natural biota, which in this system was largely flocculated particles, can contribute substantially to the nutrition of L. vannamei. There are, therefore, benefits for shrimp in the promotion of flocculated particles in L. vannamei ponds. Whether this translates into improvements in shrimp growth and production efficiency remains to be established.