Helminth Community Structure of Some Freshwater Fishes of the Cuatro Ciénegas Basin: Patterns and Processes

Abstract

Freshwater fishes are usually infected with a wide array of parasites. In particular, the helminth parasite fauna of these hosts consists of larval forms and/or adults of species included in three major phyla: Platyhelminthes (trematodes, cestodes, and monogeneans), Nematoda, and Acanthocephala. Among vertebrates, helminth parasite communities in freshwater fish are generally depauperate, i.e., communities show low species richness and abundance values. The physicochemical characteristics of the freshwater habitat, the host feeding habits, the parasite life-cycle traits, and the historical biogeography of both members of the association are the main factors that determine the parasite community structure. Patterns of community structure of freshwater fish helminths in Mexico have been described in the last two decades, although most studies were conducted in fish occurring in central and southern Mexico, and just a few were carried out in the northern region, where fish with Nearctic affinities are predominant. Water bodies of the Cuatro Ciénegas Basin (CCB), in the State of Coahuila, a characteristic intermontane desert valley in north Mexico, are inhabited by an interesting fish fauna, where most species are part of the Nearctic component. The freshwater fish helminth parasite fauna was recently described for 15 species and comprises 25 species of helminths of which 9 are digeneans, 3 monogeneans, 1 cestode, 3 acanthocephalans, and 9 nematodes. Here, the patterns and processes that determine the helminth community structure of each fish species are presented at both infracommunity and component community levels. Ecological descriptors of parasite communities, i.e., dominance, diversity, abundance, evenness, and similarity, were estimated for ten fish species for which sample size allows an analysis of their parasite communities; five of these fish species possess a Nearctic affinity, while the others belong to fish families with Neotropical affinity. Our results show that the Black bass Micopterus salmoides is the fish species with the highest diversity values at both levels. Most of the communities are dominated by a single helminth species, usually a trematode or a nematode. Remarkably, the dominant species for three parasite communities is an exotic, anthropogenically introduced helminth species, either the cestode Schizocotyle acheilognathi or the trematode Centrocestus formosanus. The processes that determine the helminth parasite community structure in the area are discussed.