The helminth communities of L. guttatus from Mazatlan Bay (MB) and Banderas Bay (BB), on the Pacific coast of Mexico, were studied during two consecutive years. A total of 536 fish were collected and 19 parasite taxa registered (six digeneans, two cestodes, nine nematodes, and two monogeneans). Infection levels of common helminth species (Helicometrina nimia, Siphodera vinaledwardsii, Tetraphyllidea gen. sp., Pseudoterranova sp., Ancyrocephalidae gen. sp. and Microcotyloides incisa) as well as the infracommunity indices varied significantly between MB and BB, and among dry and rainy seasons; however, no clear seasonal patterns were observed. Pseudoterranova larvae appeared frequently in MB, possibly because of the presence of the California sea lion in this locality. Similarity analysis did not show a clear separation of parasite species composition between both localities, which suggest that fish samples came from a single population of L. guttatus.
