A study of Gorgorhynchoides bullocki in 1,319 fish, including members of 37 species, from Bahía de Chetumal and the associated lagoonal system of Río Huach, Quintana Roo, Mexico, was initiated in order to investigate the finding of cystacanths in Eucinostomus jonesii (Perciformes: Gerreidae; slender mojarra) and Atherinomorus stipes (Atheriniformes: Atherinidae; hardhead silverside). In total, 563 fish, 254 E. jonesii and 309 A. stipes, were collected from the Laguna Río Huach system; cystacanths of G. bullocki were found to infect individuals of both species, but they were more prevalent in E. jonesii (mean abundance = 2.48; intensity = 1–27 worms) than A. stipes (mean abundance = 0.34; intensity = 1–14). A Kolmogorov–Smirnov test of similarity of distribution of helminths in the 2 populations of fishes indicated that the 2 distributions differed significantly (p < 0.0001). For E. jonesii, there was a significant difference in the mean abundance of cystacanths in relation to the month in which they were collected and in relation to the total length of host (p < 0.03 and p < 0.0001, respectively), but for A. stipes, only the relationship between mean abundance and total length of host was significant (p < 0.01). To investigate possible sources of infection for these 2 species, 756 fish from Bahía de Chetumal were examined. Definitive hosts of G. bullocki in Bahía de Chetumal include Caranx latus, Hexanematichthys assimilis, Lutjanus griseus, Selene vomer, and Scomberomorus maculatus. Eucinostomus jonesii, A. stipes, H. assimilis, S. vomer, and Sco. maculatus are new host records for G. bullocki for Quintana Roo and Mexico.