Effects of the cranial parasite Tylodelphys sp. (Digenea: Diplostomidae) on the behavior and physiology of puye Galaxias maculatus (Osmeriformes: Galaxiidae)

Abstract

Diplostomatid digeneans that inhabit the eye lens of its fish second intermediate hosts are wellknown manipulators of behaviour of their hosts. They can cause cataracts that may render their host fish to be more prone to be preyed upon by bird definitive hosts. Diplostomatids such as Tylodelphys sp. that inhabit the cranial cavity, however, up to date have not been shown to alter host behaviour of fish intermediate hosts. The goal of this study was to evaluate the potential effects of Tylodelphys sp. inhabiting the cranial cavity of Galaxias maculatus on its physiology and swimming behaviour as well as its reaction to a simulated predation threat. Blind experiments in the lab were carried out on 56 specimens that were filmed individually. The Fulton index (K) was used as a factor of nutritional status and a respirometric chamber for the oxygen consumption rates (mg O2 g-1 h-1) of the fishes. Of the 56 fish, 21 were parasitized by Tylodelphys sp. (n = 625). Parasitized and non-parasitized fishes were similar in total legth, weight, sex ratio, condition factor and oxygen consumption rates. Furthermore, the magnitude of infection was not correlated with the oxygen consumption rates of G. maculatus. Parasitized fishes swam more frequently close to the surface, whereas parasite-free fish swam more frequently at intermediate depths. When faced by simulated attack of a predator, parasite-free fish showed more frequent fleeing behaviour as well as a more intense post-fleeing activity. Collectively these results suggest that Tylodelphys sp. inhabiting cranial cavity of fish may alter their behaviour predisposing them to predation by birds.