The parasites Perkinsus spp. are relatively easily and inexpensively detected in host tissues, but available methods to detect free-living planktonic stages are technologically complex and expensive. As a result, few studies have been conducted to detect and quantify free-living stages during transmission. Here, we describe an adaptation of Ray fluid thioglycollate medium (RFTM) assay to detect and enumerate Perkinsus spp. parasites in environmental water samples. Recovery of in vitro cultured P. marinus was successful, but recovery rates were low. Filtration of water samples captured significantly more cultured P. marinus cells than centrifugation. Lipid supplementation during RFTM incubation enhanced recovery of cultured P. marinus, but not of naturally occurring Perkinsus spp. parasites. Comparisons between the modified RFTM filtration method and a more complex immunoassay revealed that the two methodologies were equally sensitive, indicating that the RFTM filtration method may be confidently applied to environmental water samples to determine relative concentrations of Perkinsus spp. parasites.