The Asian fish tapeworm, Schyzocotyle acheilognathi (syn. Bothriocephalus acheilognathi) represents a threat to freshwater fish, mainly cyprinids, across the globe. This tapeworm possesses an extraordinary ability to adapt to different environmental conditions and, because of that, from its natural geographical origin in mainland Asia, it has colonized every continent except Antarctica. It is thought that this pathogenic tapeworm was first co-introduced into Mexico in 1965 from China, with the grass carp Ctenopharyngodon idella, although the first formal record of its presence was published in 1981. Over the past 35 years, the Asian fish tapeworm has invaded about 22% of the freshwater fish in Mexico. Because fish communities in Mexico are characterized by high species richness and levels of endemism, S. acheilognathi is considered as a co-introduced and co-invasive species. In this review, we update the geographic distribution and host spectrum of the Asian fish tapeworm in Mexico. Up until December 2016, the tapeworm had been recorded in 110 freshwater fish species (96 native and 14 introduced), included in 51 genera, 11 families and 4 orders; it was also widely distributed in all types of aquatic environments, and has been found in 214 localities. We present novel data from a survey aimed at establishing the distribution pattern of the tapeworm in native freshwater fishes of two rivers in north-central Mexico, and the genetic variation among individuals of this co-invasive species collected from different host species and localities. We discuss briefly the factors that have determined the remarkable invasive success of this parasite in freshwater systems in Mexico.

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Species included in the genus Dolops (Ichthyostraca: Argulidae) have been recorded from Southern and Central Africa, Australia, and mainly from South America, with no records from Central or North America. Specimens of Dolops bidentata, previously recorded only in South America, were collected in the state of Tabasco, southern Mexico, parasitizing the common snook, Centropomus undecimalis. Here, we provide the first record of the genus and the species in North America (Mexico) and the first molecular characterization of Dolops bidentata including 1 mitochondrial and 2 nuclear DNA markers, as well as a morphological description of the specimens. The newly generated molecular data were used to preliminarily investigate the phylogenetic relationships of Branchiura and to include Dolops bidentata in a phylogenetic hypothesis. Our results fail to recover the monophyly of Dolops; however, more investigations are needed before any taxonomic change is made.