Introduction
Fish diseases represent a major challenge for aquaculture, affecting fish health, welfare and growth, ultimately reducing productivity and increasing costs. The monogenean gill parasite Sparicotyle chrysophrii is a significant threat to gilthead seabream farming in the Mediterranean (Mladineo et al., 2023; Antonelli et al., 2010) . This study examined the seasonal occurrence and mortality associated with S. chrysophrii infections in seabream reared in sea cages in the Gulf of Corinth under real farming conditions over the course of one year. The findings underscore the critical need for the implementation of seasonal parasite monitoring and targeted management interventions to effectively mitigate the detrimental impacts of Sparicotyle chrysophrii on gilthead sea bream (Sparus aurata) aquaculture.
Materials and methods
Mortalities and their causes were recorded for each sea cage used in the farming of gilthead seabream and entered into the electronic production management system of Galaxidi Marine Farm in Greece throughout the year. A statistical analysis was conducted to assess the seasonal occurrence of S. chrysophrii and the associated mortality due to parasitic infection. In addition, key production parameters were recorded, including average fish weight, stocking density, the month of introduction to sea cages, water temperature and farm unit. Group comparisons were performed using non-parametric Kruskal-Wallis tests followed by appropriate post hoc analyses. Furthermore, two machine learning techniques were applied in R to investigate the relationship between observed mortality and farming characteristics: Random Forest (via the ranger package) and Support Vector Machine (SVM) (via the e1071 package). The dataset included a wide range of numerical and categorical variables, with mortality rate as the primary response variable of interest.
Results and conclusions
The highest mortality rates attributed to S. chrysophrii infections in gilthead seabream were recorded during the summer and autumn months, with peak values observed in July and October (Figure 1). This trend suggests that the temperature profile during these seasons favors the parasite’s biological cycle, resulting in continuous reinfection of the farmed fish. Moreover, a correlation was observed between parasite-induced mortality and fish that were stocked in sea cages during the autumn and winter months. Another notable finding was the increased mortality in cages containing fish of higher average body weight, potentially linked to the absence of effective therapeutic interventions against the pa rasite. Stocking density also emerged as a significant factor influencing mortality rates, where cages with the highest stocking densities exhibited the highest parasite-related mortality (Figure 2). Ultimately, the value of the collected data lies in its potential to support the development of more robust epidemiological models, improve predictions related to climate change impacts on parasitic infections, and guide the design of more structured and targeted sampling strategies. These insights offer promising opportunities for future research directions in Mediterranean aquaculture.
References
Mladineo , I., Volpatti , D., Beraldo, P., Rigos, G., Katharios, P., Padros , F. (2023). Monogenean Sparicotyle chrysophrii : The major pathogen of the Mediterranean gilthead seabream aquaculture. Reviews in Aquaculture, 1–22. doi: 10.1111/raq.12839.
Antonelli L, Quilichini Y, Marchand B (2010). Sparicotyle chrysophrii (Van Beneden and Hesse 1863) (Monogenea : Polyopisthocotylea ) parasite of cultured gilthead sea bream Sparus aurata (Linnaeus 1758) (Pisces: Teleostei) from Corsica: ecological and morphological study. Parasitol Res., 107:389-398.