Multifaceted analysis of cymothoids parasitism, environmental stressors and heavy metal bioaccumulation dynamics in mediterranean farmed fish in Egypt

Abstract This study investigated the interactions between cymothoids parasitism, environmental stressors, and heavy metal bioaccumulation in commercially farmed fish in the Deeba Triangle area, Egypt. Over 600 fish, comprising gilthead seabream ( Sparus aurata ) and two mullet species ( Mugil cephalus and Liza ramada ), were examined during spring and summer 2023. Seasonal variations in cymothoids parasite infestation showed higher prevalence during spring ( S. aurata : 37%, mullets: 100%) compared to summer ( S. aurata : 20%, mullets: 80%). Morphological and molecular characterization identified the parasite as Livoneca redmanii , with mitochondrial 16S rRNA sequencing revealing 98.73% similarity among isolates (PQ580903-PQ580904). Water quality analysis of aquaculture ponds showed suboptimal conditions compared to the source irrigation canal, including elevated unionized ammonia (0.024–0.042 mg/L vs. 0.012 mg/L) and reduced dissolved oxygen (4.8–5.2 mg/L vs. 6.8 mg/L). Heavy metal accumulation followed consistent tissue-specific patterns (liver > gills > muscle) across five metals (Pb, Fe, Cu, Cd, Mn), with M. cephalus demonstrating the highest bioaccumulation potential. In M. cephalus liver tissue, transfer factors for Cu (175) and Fe (15.45) indicated significant metal retention. Correlation analysis in M. cephalus tissues revealed strong positive relationships between Cu-Fe ( r = 0.88) and Fe–Mn ( r = 0.78). The human health risk assessment indicated that muscle tissue consumption across all species was within safe limits (THQ ≤ 1.0). This integrated analysis provides insights into species-specific management strategies in Mediterranean aquaculture.