Reduced Lepeophtheirus salmonis larval abundance in a sea loch on the west coast of Scotland between 2002 and 2006.

A survey for planktonic sea louse larvae was carried out in Loch Shieldaig, Scotland, between 2002 and 2006, and spanned 2 successive production cycles (Cycles 1 and 2) at a local Atlantic salmon Salmo salar L. farm. The vast majority of the caligid copepodids recovered were Lepeophtheirus salmonis; however, the methodology was unable to determine the species of the caligid nauplii. Greatest densities of nauplii were found at the sampling station adjacent to the salmon farm, and larval densities were low during the fallow period of both cycles. Peaks in nauplius densities occurred around the same time in the 2 cycles, but the peaks were significantly lower during Cycle 2 than Cycle 1. Lepeophtheirus salmonis copepodid densities varied temporally, but not spatially. During most of Cycle 2, copepodid densities were significantly lower than those recovered during Cycle 1. Numbers of gravid L. salmonis at the local salmon farm correlated significantly with densities of louse nauplii and L. salmonis copepodids in the water at time lags of 0 and 1 wk, and 1 and 2 wk, respectively. This survey demonstrated a reduction in densities of L. salmonis larvae in the plankton (an indication of L. salmonis infectious pressure) between the 2 cycles and indicated that the farm was an important source of L. salmonis larvae. The application of anti-louse treatments using emamectin benzoate reduced the numbers of gravid L. salmonis at the farm, and this was the main factor influencing the apparent reduction in L. salmonis infectious pressure in the loch between cycles.

Development and application of real-time PCR for specific detection of Lepeophtheirus salmonis and Caligus elongatus larvae in Scottish plankton samples.

Lepeophtheirus salmonis and Caligus elongatus are important parasites of wild and cultured salmonids in the Northern Hemisphere. These species, generically referred to as sea lice, are estimated to cost the Scottish aquaculture industry in excess of pound 25 million per annum. There is great interest in countries such as Ireland, Scotland, Norway and Canada to sample sea lice larvae in their natural environment in order to understand lice larvae distribution and improve parasite control. Microscopy is currently relied on for use in the routine identification of sea lice larvae in plankton samples. This method is, however, limited by its time-consuming nature and requirement for highly skilled personnel. The development of alternative methods for the detection of sea lice larvae which might be used to complement and support microscopic examinations of environmental samples is thus desirable. In this study, a genetic method utilising a real-time PCR Taqman-MGB probe-based assay targeting the mitochondrial cytochrome oxidase I (mtCOI) gene was developed, which allowed species-specific detection of L. salmonis and C. elongatus larvae from unsorted natural and spiked plankton samples. Real-time PCR is a rapid, sensitive, highly specific and potentially quantitative technique. This study demonstrated its suitability for the routine identification of L. salmonis and C. elongatus in mixed plankton samples. The real-time PCR assay developed has considerable potential for use in complementing, supporting and reducing reliance on time-consuming conventional microscopic examination for the specific identification of sea lice larvae in plankton samples.