A three-year longitudinal survey reveals early life infection of farmed gilthead sea bream (Sparus aurata) by Enterospora nucleophila (Microsporea: Enterocytozoonidae)

Trabajo presentado en el 15th International Conference of Parasitology, celebrado en Copenhague (Dinamarca) del 21 al 26 de agosto de 2022.[Introduction]: Emaciative microsporidiosis due to Enterospora nucleophila is considered an emerging problem in gilthead sea bream farming. Its main impact is the severe growth retardation, normally accompanied by sustained trickling mortality, which is only noticed with high intensity of infection. The aim of the current study was to assess the possible points of entry of this intestinal parasite into the farming facilities, by using qPCR screening in a longitudinal epidemiological survey. [Methods]: Fish were sampled at different critical control points during two production cycles in Spain (C1) and Greece (C2), involving 2 hatcheries, 3 nursery conditions, 4 pre-fattening facilities, and 5 sea cage farms with different entering seasons, from egg to commercial size. Artemia and rotifers were also analysed. [Results]: After analysing 1,930 samples, the microsporidium was found in all the farms, but not in all farming events. Fish were negative for the parasite from the egg to the fry stage just after weaning in all sampled hatcheries-nurseries, no matter what type of water rearing system was used. Live prey was also negative. The first positive cases were detected in C2 when entering the nursery vs when leaving the nursery in C1. The smallest fish harbouring the parasite weighed 0.9 g. Before stocking into the sea cages, the highest prevalence of infection (100 %) was detected in a pre-fattening facility in which fish spent a longer period than usually, with an open seawater flow, without filtering. The parasite was found in all sea cages with prevalence ranging from 10 to 72.4%. [Conclusions]: The ubiquitous presence of E. nucleophila in the farms emphasize the importance of incorporating its routine detection into the management and biosecurity protocols of farms. [Funding]: ParaFishControl H2020 EU project (634429)