Helminth parasites of freshwater fishes of the Balsas River drainage basinof southwestern Mexico

This study presents the results of the first survey of the helminth parasit es in fishes in the Balsas River drainage. southwestern Mexico. A total of 25 species of helminth parasites in 13 freshwater fish species (n = 1.045) was collected between December 1995 and September 1999. The most prevalent and widespread helminth species was the Asian tapeworm Bothriocephalus ache ilognathi. Two features characterize the helminth fauna of the Balsas River basin fishes: (1) a predominance of nematode and trematode species coupled with a scarcity of monogeneans and acanthocephalans; and (2) all helminths found had previously been reported from other regions of Mexico; therefore the composition of the helminth fauna of the fishes of the Balsas River dr ainage is not very distinct from that of fishes from other previously studi ed freshwater basins in Mexico.