Sea lice is an ectoparasite that affects farmed salt water fish species globally. It is particularly problematic for farmed species held in salt water net pen cages. In Hong Kong the sea lice species of the genus Caligus infects the oral cavity of hybrid grouper and can lead to significant losses if not treated. The most common strategy used to treat this parasite in Hong Kong is repeated formalin baths, but these are logistically difficult to perform on a large scale, and not always effective. We assessed the use of SLICE® (oral emamectin benzoate product) as an alternative treatment for sea lice in hybrid grouper in Hong Kong. Our findings suggest the dose recommended for salmonids (50 µg/kg of fish for 7 days) was adequate to effectively treat this species of fish, and the effect was long lasting. We also report tissue concentrations over time to guide practitioners on appropriate withdrawal periods for this drug in this species of fish at 17 C.