We studied the distribution and abundance of Melanoides tuberculata in the Centla Swamps Biosphere Reserve. We sampled 19 lagoons, during the rainy (September October 2003) dry (April May 2004) seasons. We used the variance: Morisita's Index (δ) and the k parameter to estimate the distribution pattern space aggregation index. We registered the species 18 lagoons. A total of 13,597 individuals were collected, the greater abundance appeared during the rainy season (8,364 individuals). All populations presented an aggregated spatial distribution pattern. Abundance was inversely correlated with chemical oxygen demand and directly correlated with nitrates during the rainy season. During the dry season, abundance was inversely correlated with salinity and directly with nitrates, nitrites and pH.
