AbstractPond water quality and associated microbial biomass were studied in relation to the type of feed applied during the culture of the marine shrimpPenaeus vannamei. The feeds tested included conventional feedlot manure as well as two feeds based on bagasse, a sugarcane waste product. Physical and chemical parameters were studied during a 100 day trial in 200 m2earthen ponds. Both bagasse‐based feeds supported a significantly larger microbial community as measured by specific biomass numbers (P<0.01), ATP content (P<0.001) and amount of the particulate organic matter present on pond bottoms (P<0.025). For both bagasse‐based treatments, the estimated bacterial cell number in the flocculent layer was 3.11 ± 1012/m2, compared to the much lower cell number of 7.53 ± 1010/m2for control ponds. Harvest data suggest that bagasse forms a potential base for feeds when applied to extensive shrimp cul