Antioxidant enzyme activity and lipid peroxidation in gills of fish (Sparus aurata) upon exposure to swarms of Pelagia noctiluca

Abstract

During the last decade, massive blooms of jellyfish have occurred in the Mediterranean basin, putting great concern on cultured fish in offshore cage. Current studies enter in this task, and they consist on examining the antioxidant responses as well as lipid peroxidation and mucous secretion in gills of the gilthead sea bream (Sparus aurata). This is done upon exposure to the scyphozoan jellyfish Pelagia noctiluca at environmentally realistic densities (3, 7 and 15 individus per tanks). This finding revealed that P. noctiluca was a highly toxic organism to the cultured fish. Morphological examination showed lesions of the secondary gill lamellae in fish exposed to jellyfish. Enzymatic activities were measured after 0, 1, 2, 7, 15 and 30 days after initiating the exposure. The set of analyzed activities included catalase (CAT) and glutathione reductase (GR) activities. Lipid peroxidation was measured by quantifying malondialdehyde (MDA). Estimation of mucus secretion was done by using the phenol sulfuric acid assay protocol. The results showed that jellyfish induced antioxidant enzyme activities (CAT, GR) at different densities. Gills MDA content was significantly increased in all treated groups versus the control groups throughout the exposure periods. Our results show also that fish exposed to jellyfish swarms showed mucus hypersecretion on gills. Based on the results of this study, we consider the scyphozoan jellyfish P. noctiluca to be harmful in aquaculture system. The observed changes in analyzed parameters (especially CAT and GR activities, MDA contents and mucous production) suggest that these parameters could be useful tools in environmental monitoring programs of the aquaculture where jellyfish blooms occur.