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Abstract In the Mediterranean area, amyloodiniosis represents a major hindrance for marine aquaculture, causing high mortalities in lagoon-type based rearing sites during warm seasons. Amyloodinium ocellatum (AO) is the most common and important dinoflagellate parasitizing fish, and is one of the few fish parasites that can infest several fish species living within its ecological range. In the present study, A. ocellatum was recorded and collected from infected European sea bass (Dicentrarchus labrax) during a summer 2017 outbreak in north east Italy. Histological observation of infected ESB gill samples emphasized the presence of round or pear-shaped trophonts anchored to the oro-pharingeal cavity. Molecular analysis for small subunit (SSU) rDNA of A. ocellatum from gill genomic DNA amplified consistently and yielded 248 bp specific amplicon of A. ocellatum , that was also confirmed using sequencing and NCBI Blast analysis. Histological sections of ESB gill samples were addressed to immunohistochemical procedure for the labelling of ESB igm , inos , tlr2 , tlr4 , pcna and cytokeratin. Infected gills resulted positive for igm , inos, pcna and cytokeratin but negative to tlr-2 and tlr-4. Furthermore, ESB immune related gene response (innate immunity, adaptive immunity, and stress) in the course of A. ocellatum infection using quantitative polymerase chain reaction (qpcr) for infected gills and head kidney was analysed. Among the twenty three immune related gene molecules tested, cc1 , il-8 , il-10 , hep , cox-2 , cla , cat, casp9 , and igt were significantly expressed in diseased fish. Altogether, these data on parasite identification and expression of host immune-related genes will allow for a better understanding of immune response in European sea bass against A. ocellatum and could promote the development of effective control measures. Highlights • Gills from naturally infected ESB emphasized the presence of round/pear-shaped AO trophonts. • Immunohistochemical labelling confirmed positive for ESB igm , inos , pcna and cytokeratin but negative to tlr2 , tlr4. • Inflammation (il-8 , cc1 , cox-2) triggered novel molecules (Hep). • First demonstration of igt expression in ESB infected with AO. • Hepcidin , cc1 and igt could be potential markers for AO infection in ESB. [ABSTRACT FROM AUTHOR]

European sea bass and gilthead sea bream are two major marine finfish species reared in the Mediterranean region. Feeds for these species have high protein levels, usually supplied by fish meal. Research on alternatives to fish meal is mainly focused on plant protein feedstuffs, which are generally high in carbohydrates. Therefore, understanding the potential use of dietary carbohydrate is crucial for better utilization of such feedstuffs in the diets for these species. Factors that affect carbohydrate digestibility, metabolic utilization, as well as regulation of glucose metabolism are discussed. Data show that to ensure high digestibility, growth, and feed utilization, diets for these species should include around 20% digestible carbohydrate. Digestibility of native starch is high (above 70%) in both species, and it is further improved by processing starches (above 90%). Regarding carbohydrate complexity, it appears that European sea bass perform better with starch than glucose, while the opposite is true for gilthead sea bream. An enhancement in the activity of key enzymes of the glycolytic pathway and an increase of liver glycogen content is generally observed in the two species after feeding carbohydrates. An inverse regulation of the gluconeogenic enzyme activities with dietary carbohydrate intake is not observed in either species. [ABSTRACT FROM AUTHOR]