Comparative analysis of biomarkers and energy metabolism in parasitized and non-parasitized European seabass (Dicentrarchus labrax)

Abstract Ectoparasitic infestations present a significant challenge to aquaculture health management by disrupting the oxidative stress balance, immune defense mechanisms, and energy metabolism of European seabass ( Dicentrarchus labrax ). These effects are further influenced by seasonal environmental changes that impact both host physiology and parasite prevalence. This study assessed seasonal changes in oxidative stress, immune response, energy metabolism, growth, and tissue damage in a total of 200 European seabass collected seasonally from a marine fish farm in Damietta, Egypt. Fish showed increased oxidative stress and immune activity in the autumn, the winter, and the spring, with glutathione (GSH) peaking in the spring, while malondialdehyde (MDA) and nitric oxide (NO) levels increased in autumn and winter. Immune markers like immunoglobulin M (IgM) and lysozyme were significantly elevated in winter and spring, while interleukin-1β ( il-1β ) increased during autumn and winter. Liver energy biomarkers increased during autumn and spring compared to summer and winter. Histopathological lesions, including necrosis, hemorrhage, and inflammation, were found especially during temperature extremes. Principal component analysis (PCoA) revealed biomarker clusters linked to parasite loads and environmental stress. Seasonal infestations induce oxidative damage, immunological problems, and metabolic changes that compromise fish health. These findings highlight the significance of employing oxidative, immunological, and metabolic biomarkers as indicators of ectoparasitic stress, enabling seasonal health management measures to improve fish welfare and mitigate production losses in aquaculture.