A survey of freshwater fishes and their macroparasites in the Guanacaste Conservation Area (ACG), Costa Rica

Freshwater fish were collected mainly by electrofishing in 27 localities in rivers and streams within the Area de Conservacion Guanacaste in northwestern Costa Rica, in June 1998 (rainy season), February 1999 and March 2001 (dry season). The fish were identified and analyzed for macroparasites. Fourteen localities were in rivers draining to the Atlantic, and 13 draining to the Pacific. On the Pacific slope, three localities were seasonal streams with small catchment areas. Five localities lacked fish, probably due to effluents from volcanic areas. A total of 36 fish species were recorded, including one new to science; Poecilopsis santaelenae. The most commonly occurring species were the catfish Rhamdia rogersi (11 sites), the cichlid Astatheros alfari (10 sites), and the guppy Poecilia gillii (9 sites). A total of 25 fish species were recorded on the Pacific slope, and 26 species on the Atlantic slope. On the Pacific slope, sampling sites were at altitudes from 8 to 880 m a.s.l.; on the Atlantic slope from 205 to 675 m a.s.l. On both slopes the number of species per site decreased with increasing altitude. Fish communities at lower altitudes included species feeding on detritus and plant material as well as species feeding on invertebrates and fish. At higher altitudes, species feeding on invertebrates became increasingly dominant. At the uppermost sites, the only recorded fish species were invertebrate feeders. A total of 50 parasite taxa were recorded by necropsy and visual inspection of the fish material. Both prevalence and abundance of parasites were generally quite low. So far two species have been described as new to science; Wallinia chavarria and Paracreptotrema blancoi. During the rainy season (June 1998), 29 parasite taxa were identified from 369 dissected fish hosts. In the two dry season samples, 25 parasite taxa were identified from 277 hosts in 1999, while 26 taxa were found in 450 hosts in 2001. Twelve parasite taxa were found only in the wet season, 21 taxa were found only in the dry season, while 17 taxa were found in both seasons. The parasite data were analysed with regard to how host diversity, host sample size and sampling season (dry or wet) affects parasite diversity, providing the following conclusions. Within each season, the number of host species analysed is the most important factor determining the recorded number of parasite taxa. Within each host species, it appears that increasing the number of analysed individual hosts from one site and season is as important for the number of recorded parasite taxa as adding hosts from different sampling sites or seasons. Our data also show that the number of parasite taxa recorded in fish (all host species) sampled in the rainy season is lower than in samples from the dry season. Finally, there is a large turnover of parasite taxa between seasons. The macroparasite fauna of fishes in Guanacaste rivers generally follows the biogeographical patterns and history of their hosts. The parasite fauna of the cichlids resemble the fauna reported from southern Mexico, while the parasites recorded in the characid fish species show the connection to the parasites of characids in South America. The parasites recorded in the Cyprinodontiformes fishes (families Poeciliidae, Rivulidae, etc) in this study are consistent with the distribution of these parasites in middle America (Mexico to Panama). KEY WORDS : Guanacaste Conservation Area (ACG), Costa Rica freshwater fishes, Macroparasites, faunal survey, Costa Rica, Guanacaste Conservation Area (GCA), Mellom- Amerika, ferskvannsfisk, makroparasitter, faunakartleggin