Parasite infestation in red hybrid Tilapia across Sarawak: Morphological, DNA barcoding and water quality assessment under different culture systems.

Red Hybrid Tilapia (RHT) is a vital species in aquaculture but remains highly vulnerable to parasitic infestations, which can compromise productivity and overall fish health. This study assessed the prevalence, intensity, and species identification of ecto- and endoparasites in RHT across different aquaculture systems in Sarawak from May to December 2022. A total of 120 RHT samples were analyzed using both morphological and molecular approaches. Results indicated a high prevalence of ectoparasites in ST1, ST2, and ST3 (100 %) compared to ST4 (96.67 %). Trichodina spp. was the most common ectoparasite (70.83 %), while molecular analysis identified Cichlidogyrus thurstonae. Endoparasites were detected only in ST1, with greater occurrence in the intestine (53 %) than in the stomach (40 %). Despite being morphologically identified as a Digenean Trematode, BLAST and phylogenetic analysis failed to provide a definitive match, suggesting a potentially novel species. Interestingly, water quality parameters did not vary significantly across sites, implying that parasite prevalence is more influenced by aquaculture system design, stocking density, and management practices rather than environmental factors alone. Poor biosecurity, high fish densities, and insufficient parasite control measures may contribute to high infestation rates. This study highlights the need for enhanced biosecurity protocols, regular parasite monitoring, and improved management strategies to mitigate parasitic infections. The findings provide valuable baseline data for sustainable RHT farming, emphasizing the importance of proactive health management to ensure long-term productivity and food security.