Host-Parasite interactions in the Arabian Gulf: a morphological and molecular study of Cymothoa pulchrum in Parastromateus niger

This study documents the first record of the parasitic isopod Cymothoa pulchrum Lanchester (Proceedings of the Zoological Society of London 534–574, 1902) infesting the buccal cavity of the black pomfret (Parastromateus niger) in the Arabian Gulf, Saudi Arabia. A total of 750 fish specimens were examined between January and December 2019, revealing 7.3% prevalence (55/750). Morphological characterization using light and scanning electron microscopy confirmed the species’ identity, with key diagnostic features including bilaterally symmetrical pereonites, robust pereopods, and a pleotelson (2.0 × 1.5 mm length by width). Molecular analysis of the mitochondrial 16 S rRNA gene (GenBank: MK505567) showed 99% similarity to C. pulchrum isolates from Japan (LC159448, LC160307). Phylogenetic reconstruction placed C. pulchrum within a clade of Indo-Pacific buccal cavity specialists. The parasite caused complete erosion of host tongue tissues, highlighting its threat to fisheries. These findings expand the known host range of C. pulchrum and underscore the need for monitoring parasitic infestations in tropical marine ecosystems.