[Population biology of Posthodiplostomum namum Dubois, 1937 (Trematoda, Diplostomidae) in Jenynsia lineata and Cnesterodon decemmaculatus (Pisces, Atheriniformes), of Chis-Chis Lagoon, Province of Buenos Aires, Argentina]. / Biología Poblacional de Posthodiplostomum nanum Dubois, 1937 (Trematoda, Diplostomidae) en Jenynsia lineata y Cnesterodon decemmaculatus (Pisces, Atheriniformes), de la Laguna de Chis-Chis, Provincia de Buenos Aires, Argentina.

The characteristics of the population dynamics of Posthodiplostomum nanum have been studied in two of its intermediate hosts, using prevalence, intensity and maturity of the metacercariae, considering the influence of the water temperature. In addition to this some ecological implications are described. There were made 18 samples monthly or bimonthly from may 1986 until march 1989, 1113 fishes were captured out of which 956 metacercariae were obtained. P. nanum was present along the year, having significant seasonal variation in prevalence and intensity of infestation. It was observed that the water temperature is a relevant factor in the maturation of the parasite. The values of the prevalence and intensity of infestation were higher in Jenynsia lineata than in Cnesterodon decemmaculatus. This could be explained by various factors: a) distribution of the first intermediate host; b) behavior of the second intermediate host and c) individual physiological differences of each host, specially in relation to reproduction. The relation S2/X fluctuated during the whole year, indicating the recruitment-period (autumn, spring) and the nonrecruitment-period (winter, summer) of metacercariae.