Fish-parasite interactions: Lessons from the Mediterranean aquaculture

Abstract

Spanish aquaculture is nowadays a strong farming industry, with ca 60,000 tonnes produced annually. Gilthead sea bream (Sparus aurata), European sea bass (Dicentrarchus labrax) and turbot (Scophthalmus maximus) gather more than 90 % of the marine fish production and most of the research efforts. Aquaculture conditions may aggravate natural infections, spread out diseases and disturb the equilibrium between hosts and pathogens, as therefore fish production may be endangered by diseases. The massive application of vaccination programs and other treatments against bacterial pathogens, have contributed to upstage parasites as the second cause of mortality and morbidity. The impact of parasites is not only due to direct mortality but also to weight loss, poor conversion rates, delayed growth and reduced marketability. Infections are the result not only of fish and pathogen interactions, but also are due to environmental and anthropogenic factors. High culture densities and suboptimum water conditions, or the use of materials, which allow the attachment, and proliferation of parasite stages or intermediate hosts, open opportunities for parasites to proliferate above epizootic thresholds and cause disease. In addition, the high density of farms and the global trade of fish and their gametes, or the market of pet shops and exotic species, facilitate colonization of new areas and hosts by exotic parasites. Thus, parasitic diseases are constantly emerging as production constraints both in new and in relatively mature production systems. Monogeneans, ciliates and flagellates are the most prevalent, whereas the presence and impact of myxozoans and coccidians have increased constantly in the last years. The myxozoans Enteromyxum leei and E. scophthalmi constitute a real threat for sparids and turbot cultures, respectively and the scuticociliate Philasteristes dicentrarchi produces problems in turbots. In spite of the latest advancements in our knowledge of the biology of parasites and pathology of the infections, the struggle against fish parasites in production systems is far from being solved. This is way the Fish Pathology group of IATS is devoted to the study of parasites affecting marine aquacultured fish in a multifaceted way. The research lines include 1) the development of reliable, fast and accurate diagnostic methods, 2) basic studies to understand the life cycle, transmission and epidemiology of the infections, 3) structural, genetic and antigenic characterization of parasites, 4) generation of treatment and prophylactic tools including vaccines, immunomodulation and genetic selection, and 5) the study of the mechanisms and key genes involved in the immune response and resistance to parasites.