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The rapid development of intensive fish farming has been associated with the spreading of infectious diseases, pathogens and parasites. One such parasite is Sparicotyle chrysophrii (Platyhelminthes: Monogenea), which commonly infects cultured gilthead seabream ( Sparus aurata )-a vital species in Mediterranean aquaculture. The parasite attaches to fish gills and can cause epizootics in sea cages with relevant consequences for fish health and associated economic losses for fish farmers. In this study, a novel stratified compartmental epidemiological model of S. chrysophrii transmission was developed and analysed. The model accounts for the temporal progression of the number of juvenile and adult parasites attached to each fish, as well as the abundance of eggs and oncomiracidia. We applied the model to data collected in a seabream farm, where the fish population and the number of adult parasites attached to fish gills were closely monitored in six different cages for 10 months. The model successfully replicated the temporal dynamics of the distribution of the parasite abundance within fish hosts and simulated the effects of environmental factors, such as water temperature, on the transmission dynamics. The findings highlight the potential of modelling tools for farming management, aiding in the prevention and control of S. chrysophrii infections in Mediterranean aquaculture., Competing Interests: We declare we have no competing interests., (© 2023 The Authors.)

Meagre Argyrosomus regius is a potential candidate for Mediterranean aquaculture diversification, although several health issues still represent important bottlenecks for its sustainable production, including systemic granulomatosis (SG). To evaluate the SG progression in meagre during a 10 mo period of cage ongrowing, a histopathological investigation was carried out on 108 meagre fed 3 different diets (commercial pellets, hydrated commercial pellets and defrosted sardines). Histological sections of the gills and visceral organs were examined and lesions referable to SG scored from 1-3 according to the severity of the granulomatosis. The kidney and liver were the most affected organs, showing the highest percentage of positivity for granulomas and severity of lesions along the whole observation period. Using a statistical mixed model (GLMM) followed by odds ratio analysis, an effect of diet and temperature was found: the severity of liver and digestive tract SG scores decreased in the Cage 3 group (defrosted sardines) and with increasing temperature (p < 0.05, negative estimates, odds ratio <1). These observations, in accordance with the literature, suggest that SG in meagre could be related to nutritional-metabolic factors with the possible influence of environmental factors such as temperature.