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Diseases of Aquatic Organisms

    DAO prepress abstract   -  DOI:

    Effect of light on the trematode Himasthla elongata:from cercarial behaviour to infection success

    Simão Correia, Rosa Freitas, Xavier de Montaudouin, Luísa Magalhães*

    *Corresponding author:

    ABSTRACT: The cockle Cerastoderma edule, a socioeconomically important bivalve of the northeast Atlantic, is host to several trematodes, including Himasthla elongata. In the life cycle of this trematode, cercariae (free-living stages) emerge from the first intermediate host, a snail, to infect cockles as second intermediate hosts. During their lifespan (less than one day), cercariae must ensure successful host-to-host transmission via the surrounding water and therefore are exposed to and impacted by different environmental conditions, including abiotic factors. Given the light:dark cycle is one of the major drivers of aquatic life behaviour, this study aimed to determine the influence of light on cercariae and host behaviour based on 2 hypotheses. First, by having a benthic second intermediate host, these cercariae will display a photonegative orientation and conversely, the host behaviour will not be influenced by light. Results showed cercariae display a photopositive orientation (first hypothesis rejected), displaying movements towards light. The second host activity (evaluated by oxygen consumption) was similar among conditions, i.e. dark vs. light (hypothesis accepted), but they acquired more parasites when experimentally infected in the dark. This light-dependent infection of the host is explained by a change of cercarial behaviour when exposed to light, decreasing their infection success. This study highlights trematode responses to external conditions may be linked to successful life cycle completion rather than being altered by the host habitat. It was emphasized that light influence on cercarial behaviour resulted in an increased infection success that may affect trematodes population dynamics and their distributional range.