Ceratothoa oestroides has become a threat to cage-reared fish, in particular sea bass, where high fish density provides optimal conditions for transmission. It has significant impact on fish health and economical gain often leading to mass mortalities of juvenile fishes. Current management measures are often unpractical and labour-intensive, with no long-lasting protection. There are currently no effective, low environmental impact or consumer-safe synthetic or natural compound available to use as treatment against the parasite. In this study, synthetic and natural compounds were tested to identify whether they could be candidates for alternative treatment using the LC50 (Lethal Concentration 50) approach where concentration of the chemical that kills 50% of the test animal (Ceratothoa) would be used during the observation period. The potential toxicity to the host (sea bass) was also tested. All the candidates were found to be safe for the sea bass, therefore are promising candidates for treatment.