Predicting infestation parameters and impacts of caligid copepods in wild and cultured fish populations

Abstract

The intensity and timing of infestation events of caligid copepods in wild or cultured fish populations may be predicted from previous local production of nauplius I of the parasite. However, this relationship is not well established, the spatial scales over which it operates are unclear, and the role of host reactions to the inv-ding copepodid is unknown. Rate of development (and population structure), generation time and rate and actual reproductive output are temperature-dependent. In Ireland between five and seven generations of Lepeophfheirus salmonis (Krqer) can develop annually and generation time varies from over 120 days in winter to 23 days in summer. Host reactions may affect the rate of development of the parasite but are less important than temperature. Host reactions may also cause parasite mortality, but this effect is specific for individual host parasite associations. The distribution of L. salmonis in cultured host populations is typically normal but is very over-dispersed in wild populations with heavy infestations. Parasiteinduced morphological damage to the host is correlated with physiological impacts. Physiological effects are present even when morphological damage is slight and so intermittent chemotherapeutic control of infestations cannot prevent some parasite impact from occurring.

Population dynamics of salmon lice Lepeophtheirus salmonis on Atlantic salmon and sea trout

“…Along other coasts of the Atlantic ocean, water temperatures seem to be generally within this range but with lower temperatures in the summer further north in Norway (seasonal temperature range: 2 to 13°C, Rikardsen 2004) and along the NorthEast Atlantic coast (seasonal temperature range: 2 to 14°C, Hogans & Trudeau 1989), and higher winter temperatures on the west coast of Scotland and Ireland (seasonal temperature range: 5 to 16°C, Tully 1992, Ritchie et al 1993, Heuch et al 2003. The minimum development times of both eggs (τ E ) and pre-infective planktonic larval stages (τ PI ) are well described over the whole of this ecologically relevant temperature range using the Belehrádek function, while models suggested previously (Tully 1992, Boxaspen & Naess 2000 poorly fit observations at high water temperatures (T > 12°C). A weakness in the current knowledge of the minimum development times of the parasitic stages is the lack of studies at low temperatures (T < 7°C).…”

“…Despite the economic and potential ecological importance of Lepeophtheirus salmonis, relatively little work has been carried out on population dynamic models for developing control strategies in fish farms and evaluating the potential impact of transmission from farmed fish to wild host populations (but see Tully 1992, Heuch & Mo 2001, Tucker et al 2002. The life history of L. salmonis suggests that stage-structured population models could be developed along similar lines as models used for non-parasitic copepods (e.g.…”

Identifying epidemiological factors affecting sea lice Lepeophtheirus salmonis abundance on Scottish salmon farms using general linear models

“…Water temperature has been cited in several studies as an important determinant of sea lice abundance (Tully 1989, Johnson & Albright 1991, Tully 1992, Boxaspen 1997, Tucker et al 2000, Mustafa et al 2001). However, at the level of site-year analysis across a range of sites in Scotland, it does not appear to be a significant explanatory factor.…”

Optimization and field use of a bioassay to monitor sea lice Lepeophtheirus salmonis sensitivity to emamectin benzoate

“…Patterns of L. salmonis dispersal, recruitment, and treatment may influence population dynamics and the spread of genes conferring resistance to EMB. As many as 5 or 6 successive generations of L. salmonis are possible in 1 yr (Tully 1992), and the infective planktonic copepodid stage can be transported many kilometers from a point source (Murray & Gillibrand 2006); therefore, it is unlikely that a single population or generation of sea lice is present in any one region of the Bay of Fundy at a given time. Unlike laboratory populations of sea lice, where individuals of the same generation can be chosen for inclusion in a bioassay, under field conditions it is likely that sea lice collected for the bioassays are of mixed genetic backgrounds.…”