Parasite induced behavioural changes in fish

[摘要] English: Numerous studies have been conducted on the hypothesis of parasites influencing thebehaviour of their hosts. Many authors have been bias in trying to prove that this is aform of manipulation and that parasites increase their transmission success bychanging host behaviour. Not much research has been conducted in Africa regardingparasite induced behaviour. During the present study fish were collected from theOkavango and Orange-Vaal River Systems, respectively situated in Botswana andSouth Africa. Within these ecologically diverse systems a wide variety of fish werefound to be infected with diplostomatid metacercariae occurring inside their eyes and /or brains. These digenetic trematodes are known to cause blindness and otherpathological effects, known as diplostomiasis, especially in fish reared in aquaculture.Diplostomatids have a three-host life cycle which involves different species of snails,fishes and piscivorous birds. Fish act as the second intermediate hosts and need to beeaten by a piscivorous bird in order for the diplostomatids to be trophically transmittedand the life cycle to be completed. Seven different metacercarial types and cysts wereidentified and some were collected from both the eyes and brains of infected fishspecies. The results signified a moderate prevalence of these parasites amongst thedifferent fish species, whilst the intensity of infection proved to be low. No markedaltered pathology was observed in infected fish brains but noticeable histopathologicalchanges were noted within eyes infected with diplostomatid cysts. To determine theeffect these infections have on the behaviour of natural populations of fish, twobehavioural experiments were conducted. The results indicate that infected fish showsimilar behaviour than uninfected fish and therefore the null hypothesis (Ho) isaccepted.

[发布机构] University of the Free State