Spatial and temporal variations in parasite prevalence and infracommunity structure in herring (Clupea harengus L.) caught to the west of the British Isles and in the North and Baltic Seas: implications for fisheries science.

Herring Clupea harengus L. viscera were examined for endoparasitic infections as part of a multidisciplinary stock identification project (WESTHER, EU Contract no. Q5RS-2002-01 056) which applied a range of stock discrimination techniques to the same individual fishes to obtain comparable results for multivariate analysis. Spawning and non-spawning adults, and juvenile herring were caught, over 3 years, by commercial and research vessels from numerous locations to the west of the UK and Ireland, along with control samples of spawning fish from the eastern Baltic Sea, and juveniles from sites in the eastern and western North Sea, and the north of Norway. The metacercariae of two renicolid digeneans (Cercaria pythionike and Cercaria doricha), one larval nematode (Anisakis simplex s.s.) and one larval cestode (Lacistorhynchus tenuis) were selected as tag species. Results were compared with those from herring collected between 1973 and 1982, which suggested remarkable stability in the parasite fauna of herring in the study area. These species were used to compare the parasite infracommunities of spawning herring. A significant variation in infracommunity structure was observed between different spawning grounds. These results suggest that the parasite fauna of herring are spatially variable but remain temporally stable in both the short and long term. Significant differences in prevalence and abundance of infections and comparisons of parasite infracommunity enabled the separation of putative herring stocks west of the British Isles. Distinctive patterns of parasite infection in two different spawning groups off the north coast of Scotland suggest that this area is occupied by two spawning populations, one recruiting from the west of Scotland, the other from outside this area, and most likely from the eastern North Sea. The distribution patterns of L. tenuis, C. doricha and C. pythionike suggest the potential for fish that spawn in three distinct International Council for the Exploration of the Seas (ICES) management units to be present in mixed aggregations found over the Malin Shelf, with significant implications for management in this area.

Isolation of a novel fish thymidylate kinase gene, upregulated in Atlantic salmon (Salmo salar L.) following infection with the monogenean parasite Gyrodactylus salaris.

Analysis of differential gene expression in salmon (Salmo salar) blood following infection with the monogenean parasite Gyrodactylus salaris, resulted in the isolation of a thymidylate kinase gene not previously described from fish and which showed similarity to an LPS-inducible thymidylate kinase gene isolated from mouse macrophages. This salmon TYKi-like gene may play a role in an innate generalised response to pathogen infection as it was upregulated in salmon following infection with the parasite, and also in response to injection with the immunostimulants LPS and Poly I:C, used to emulate bacterial and viral infections, respectively. The possible role of this gene in the biosynthesis of mitochondrial DNA in activated macrophages, in response to G. salaris infection is discussed.

Gene expression profiles of some immune relevant genes from skin of susceptible and responding Atlantic salmon (Salmo salar L.) infected with Gyrodactylus salaris (Monogenea) revealed by suppressive subtractive hybridisation.

Suppressive subtractive hybridisation was used to examine the genetic basis of susceptibility and resistance of the Atlantic salmon (Salmo salar) to Gyrodactylus salaris infection. Selected immune relevant genes are listed and two genes, for myeloid leukemia differentiation protein (Mcl-1) and opioid growth factor receptor (OGFr), obtained from the susceptible salmon library were characterised. Both sequences showed high amino acid identity and similarity with human and mouse isoforms, and their possible involvement in the response of salmon to G. salaris is discussed. Quantitative reverse transcriptase-PCR was performed for both genes. Upregulation of Mcl-1 in B1 backcross salmon of the susceptible phenotypic category compared with resistant salmon was demonstrated. The possible relationship of the salmon Mcl-1 and cytokines (interleukin 1beta) in the G. salaris-induced host response is discussed. Potential involvement of OGFr in the depletion of mucous cells during prolonged and heavy G. salaris infection, via suppression of DNA synthesis and profound decrease in basal cell proliferation, is proposed. However, only two of six susceptible fish showed high upregulation of OGFr, which might indicate that its expression is localised to sites of wounds resulting from a heavy burden of G. salaris.

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.

Identification and characterisation of the genomic segment 7 of the infectious salmon anaemia virus genome.

The isolation and characterisation of a gene encoding the putative matrix proteins of infectious salmon anaemia virus (ISAV) is reported. Following identification of an ISAV-specific sequence from a cDNA library, RACE-PCR was used to identify a mRNA transcript of approximately 1.2 kb containing the ISAV consensus sequence GCTAAGA at the 5' end. Although the cDNA transcript and its putative protein product did not possess high homology with other orthomyxoviral sequences, similarity to a paramyxovirus fusion glycoprotein and viral cell surface proteins was identified. The size of this transcript suggested that it was derived from segment 7 of the ISAV genome and encoded the matrix proteins. Like syntenic segments of other orthomyxoviruses, this segment was shown to encode at least two matrix proteins, M1 and M2. The existence of M1 and M2 ISAV mRNA was demonstrated by RT-PCR and sequencing, with the M1 transcript being more abundant than the M2 in infected cell cultures, as is found in other orthomyxoviruses. Nucleotide sequence comparison of segment 7 of the ISAV genome from isolates of different geographic origin indicated it to be the one of the most variable of the ISAV genes characterised to date.