​Identification of Gnathiid Isopods as Ectoparasites of the Brown-spotted Grouper Epinephelus chlorostigma from the Red Sea of Saudi Arabia

Background: Gnathiids are considered excellent ectoparasites widely distributed along the fish body with a biphasic life cycle including parasitic larval stages and free-living adults. This study focused on gnathiids infecting the brown-spotted grouper fish and confirming the identity of the host species.
Methods: Twenty Epinephelus chlorostigma (Serranidae) were collected from the Red Sea Coast (especially off Jeddah, Saudi Arabia) and examined for gnathiid fish parasites. Species identification of the larvae was based on morphological criteria of Smit and Basson (2002). In contrast, the taxonomy of fish species was supported by amplification and sequencing of host DNA via the mitochondrial DNA genes (COI and 16S rRNA) using gnathiids’ blood meals. Result: Praniza larvae of a gnathiid isopod were collected from the gill chambers of the examined fish. The prevalence rate was 60% and mean intensity of the pranzia larvae was 16. The pranzia larva is described microscopically and distinguished by large body size (3.51-5.90 mm), the presence of 8th teeth in the mandible, maxilliped with 5-7th teeth on the first palp and the endite hooked, pleotelson with concave anterolateral margins and rami of uropods extend its apex. The recovered larvae could be identified as pranzia larvae of Gnathia pantherina Smit and Basson, 2002 due to the morphological resemblance. The host species identity was confirmed molecularly with COI and 16S rRNA genes and showed highly stringent criteria with the previously E. chlorostigma sequence data. The obtained host DNA sequences were deposited in NCBI database under accession numbers ON384530.1 for COI and ON384544.1 for 16S rRNA.
