Dr. George-Nascimento-Failla, Mario

Galaxias maculatus is an abundant freshwater fish species in Chilean continental waters where it plays important ecological functions, yet few parasitological records of this species exist in Chile and all of them cover a very limited geographic range. The objective of this study was to assess large scale geographic variation in composition of parasite infracommunities of Galaxias maculatus. Specifically, parasite infracommunities of this species were compared among 11 locations across 9 degrees of latitude and 3 ecosystem types (lake, river and estuary). Most taxa found had been previously reported in Chile and Argentina. However, this is the first report for Tylodelphys sp. in this host in Chile. Furthermore, the cranial parasite Tylodelphys sp. had the highest overall prevalence and abundance compared to other parasite species. Despite the fact that the abundance of Tylodelphys sp. was not significantly correlated with Fulton’s condition factor of fish, infected fish seem to have a better body condition compared to uninfected ones. The most important source of variation in composition of infracommunities was the sampling location. Furthermore, fish from lakes have a different composition of parasite infracommunities mainly due to higher abundances of Tylodelphys sp.

Diplostomatid digeneans are well-known manipulators of the behavior of their intermediate hosts. Unencysted metacercariae of Tylodelphys sp. inhabit the cranial cavity of the fish Galaxias maculatus; however, to date they have not been documented to alter their host behavior. The goal of this study was to evaluate the potential effects of Tylodelphys sp. inhabiting the cranial cavity of Galaxias maculatus on host physiology and swimming behavior as well as its reaction to a simulated predation attempt. Blind experiments in the lab were carried out on 56 fish that were filmed individually. The Fulton condition factor (K) was used as an approximation of nutritional status and a respirometry chamber was used to evaluate oxygen consumption rates of fish. Of the 56 fish, 21 were parasitized by Tylodelphys sp. (mean intensity = 30, range from 1 to 101). Parasitized and non-parasitized fish were similar in condition factor and oxygen consumption rates. Furthermore, the oxygen consumption rate of G. maculatus was not correlated with the abundance of Tylodelphys sp. However, parasitized fish more frequently swam close to the water surface, whereas non-parasitized fish more frequently swam at intermediate depths. When faced with a simulated predator attack, unparasitized fish showed more frequent fleeing behavior as well as a more intense post-fleeing activity. Collectively, these results suggest that Tylodelphys sp. inhabiting the cranial cavity of fish may alter their behavior predisposing them to predation by birds.