A review of the population biology and host-parasite interactions of the sea louse XXXX (Copepoda: Caligidae).

@entity281 @entity25282 @entity2631 @entity277
@entity25282 is a specific parasite of salmonids that occurs in the Atlantic and Pacific Oceans. When @entity277 are heavy fish mortality can occur although the factors that are responsible for causing epizootics, especially in wild salmonid populations are still largely unknown. Over the past 20 years this parasite has caused significant economic losses in farmed salmon production and possibly in wild salmonid populations locally. Understanding the connectivity between populations is crucial to an understanding of the epidemiology of @entity281 and for management of @entity281 in aquaculture. Data from genetics, pesticide resistance, larval dispersal models and spatial and temporal patterns of @entity277 in wild and farmed hosts suggests a spatially highly structured metapopulation the components of which have different levels of connectivity, probabilities of extinction and influence on the development of @entity2631 . The population structure is defined mainly by the dispersal dynamics of the planktonic stages and the behaviour of the host. Until recently virtually nothing was known about the relationship between the parasite and the host, or how the host may influence lice at local or population level. Typically, impacts on the host have usually been reported in terms of pathological lesions caused by attachment and feeding of the adult stages, as well as localised mild epithelial responses to juvenile attachment. However many studies report pathology associated with severe @entity277 . Recent new studies on the host-parasite interactions of @entity25282 have shown that this parasite induces stress-related responses systemically in the host skin and gills and that the stress response and immune systems are modulated. In the second part of this review, these new studies are presented, together with results from other host-parasite model systems where data for caligid sea lice are missing. One of the most revealing methods reported recently is the application of a net confinement stressor to examine modulation of the stress response and immune system of the host fish. This approach has shown that although until now, infective stages of @entity25282 were not thought to affect the host, they do induce systematic effects in the host that result in a stress response and modulated immune system. Host-parasite interactions affecting these stress responses and the immune system may be key factors in facilitating epizootics by reducing the host's ability to reject the parasites, as well as reducing disease resistance under some environmental conditions. The host-parasite interaction therefore needs to be incorporated into any model of population structure and dynamics.
