Molecular characterization and phylogenetic analysis of parasitic copepoda; Ergasilus sieboldi isolated from cultured gilthead sea bream (Sparus aurata) in Egypt, associated with analysis of oxidative stress biomarkers

Parasitic copepods are common damaging ectoparasites of cultured marine fish that induce high mortalities in fish farms. The present study aimed to identify the cause of mass mortalities of cultured gilthead sea bream ( Sparus aurata ) as one of the highly valuable cultured marine fish species in Egypt. Parasitological examination demonstrated Ergasilus sieboldin ( E. sieboldi ) adult females of (1.3 ± 0.01 mm, n = 55) mean body length and (0.53 ± 0.04 mm) body width, lodged in the gill filaments of the forty examined fish with a pair of strong clawed antennae. The detected parasite has six segmented antennules and consists of cephalosome followed by four divided thoracic segments that narrow posteriorly, five pairs of swimming legs, genital segment, abdominal segments followed by furcal rami with unequal caudal setae and two egg sacs at the end of the body. The collected E. sieboldi were confirmed by molecular characterization and phylogenetic analysis based on 28S rDNA sequencing. The obtained sequence in this study was registered in the GenBank with (OM812074) accession number as a first sequence of E. sieboldi from Egypt. Oxidative stress biomarkers in the gills of the parasitized fish were evaluated to describe the host defense mechanisms against E. sieboldi infestation. The current study demonstrated decreasing in reduced glutathione (GSH) content and activity of the anti-oxidant enzyme catalase (CAT), as well as elevation in the level of malondialdehyde (MDA) due to exposure to oxidative damage that might have a role in the tissue damage and dysfunction.