The San Pedro-Mezquital River basin in Nayarit, Mexico has the majority of freshwater prawns of the genus Macrobrachium reported for the Mexican Pacific coast. Six species of freshwater shrimp are reported Macrobrachium americanum, M. occidentale, M. digueti, M. michoacanus, M. hobbsi and M. tenellum. The higher richness and diversity of freshwater prawns are found on the coastal plain. The presence of prawns in relation to the altitudinal gradient is discussed.