New host and locality records of freshwater fish helminth parasites in river basins north of the Transmexican Volcanic Belt: another look at biogeographical patterns

Freshwater fish helminths have been studied for more that 80 years in Mexico, and currently the inventory of this parasite fauna is nearing completion. Between 1999 and 2006, we studied 958 freshwater fishes belonging to 34 species in 36 localities distributed along 9 states of the Mexican Republic, north of the Transmexican Volcanic Belt. In total, 25 helminth taxa were found, including 9 digeneans, 6 nematodes, 4 monogeneans, 5 cestodes, and 1 acanthocephalan. Of the 25 species of helminths, 12 were found as larval stages while 13 were found as adults. A large number of hosts (582, i.e., 60.7%) were uninfected with helminth parasites. The data we present here is then used in combination with other recently published parasite surveys conducted in northern Mexico to revise our understanding of the biogeographical patterns of the freshwater fish parasite fauna in an area inhabited predominantly by Nearctic freshwater fishes.