Amoebic gill disease (AGD) in farmed Atlantic salmon is caused by the amoeba Paramoeba perurans. The recent establishment of in vitro culture techniques for P. perurans has provided a valuable tool for studying the parasite in detail. In this study, flow cytometry was used to generate clonal cultures from single-sorted amoeba, and these were used to successfully establish AGD in experimental Atlantic salmon. The clonal cultures displayed differences in virulence, based on gill scores. The P. perurans load on gills, determined by qPCR analysis, showed a positive relationship with gill score, and with clonal virulence, indicating that the ability of amoebae to proliferate and/or remain attached on gills may play a role in virulence. Gill scores based on gross signs and histopathological analysis were in agreement. No association between level of gill score and specific gill arch was observed. It was found that for fish with lower gill scores based on histopathological examination, gross examination and qPCR analysis of gills from the same fish were less successful in detecting lesions and amoebae, respectively.
Most studies that monitor a biological parameter over time in fish are based on the culling of animals and subsequent tissue sampling or the use of complicated surgical procedures such as cannulation of the dorsal aorta. The former method suffers from the large inter-individual variability typically seen in outbred fish, whilst the latter requires highly skilled operators and is not possible with small fish. We describe here a novel and simple method based on non-lethal collection of blood samples from the same individual, allowing improved data quality and reduction in number of animals used without the need for surgical procedures. The frequency and volume of blood collected repeatedly was adjusted to limit the decrease in the percentage of blood packed cell volume (PPCV). The stress response evaluated by measuring the expression of the heat shock proteins 90αb1, 70KDa and the cytochrome p450 family 17 A1 in blood cells by qPCR. Expression levels increased during the PPCV decline and returned to their basal level after adjustment of the sampling procedure. This study demonstrates that a non-lethal sampling procedure can be used for salmonid fish and gene expression in blood cells can be monitored over time from the same individual.
Amoebic gill disease (AGD), caused by Neoparamoeba perurans, is one of the main health challenges for the global Atlantic salmon (Salmo salar Linnaeus, 1758) farming industry (Oldham, Rodger, & Nowak., 2016; Rodger, 2014). This parasite's presence in a number of other marine fish species (Oldham et al., 2016), including cleaner fish species used for the biological control of sea lice in Atlantic salmon farms (Haugland, Olsen, Rønneseth & Andersen, 2017), has resulted in the emergence of new challenges for the industry especially as high mortalities can result if AGD is left untreated (Munday, Zilberg, & Findlay, 2001). Current approaches for controlling AGD are resource-demanding and labour-intensive, involving numerous treatments throughout
This book chapter discusses the various aspects of amoebiosis caused by Neoparamoeba perurans: description of the disease, causative agent, risk factors, diagnostic techniques, transmission, population dynamics of the reservoir hosts, disease control and prevention, and development of chemotherapeutics.
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