Emamectin Benzoate Treatment of Hybrid Grouper Infected With Sea Lice in Hong Kong.

Sophie St-Hilaire,Stephen Chi Ho Chan,William Furtado,Tzu Hsuan Cheng,Ka Man Chan,Giana Bastos Gomes,Kwok Zu Lim,Chi Fai Leung

doi:10.3389/fvets.2021.646652

Abstract

Sea lice (Copepoda: Caligidae) are ectoparasites which negatively impact marine aquaculture species around the world. There are a limited number of treatments licensed for use against sea lice in tropical and semi-tropical farmed fish species. Emamectin benzoate (EB) was an effective pharmaceutical drug against sea lice infestations in several salmon industries before resistance to the product developed. This drug has not been extensively tested in marine fish within Asia. The objective of this study was to determine whether this drug could be used to treat oral infections with sea lice in hybrid grouper (Mycteroperca tigris × Epinephelus lanceolatus) cultured in saltwater net-pen sites in Hong Kong. We observed an overall reduction in sea lice infections over time, starting on the last day of the treatment up to the end of our study (i.e., 14 days after the last EB treatment). We also observed a large variation in concentrations of EB in fish on the last day of the treatment, which provides an explanation for the variation in response to the treatment. It also suggests that distribution of the medication to fish in saltwater net-pens is difficult, especially when medication is hand-mixed in the feed and possibly unevenly distributed in the daily rations. Overall, this study provides preliminary evidence that EB could be used to treat sea lice found in Hong Kong and potentially in other regions of SE Asia.

Highlights

Sea lice are copepod parasites of economically important marine finfish found around the world
All fish sampled on farms had some level of infection with sea lice prior to starting the treatment
Two farms had a decline in the proportion of infected fish not treated with Emamectin Benzoate (EB) (Figure 4)

Summary

Introduction

Sea lice are copepod parasites of economically important marine finfish found around the world. Some sea lice species affect only certain species of fish (i.e., Lepeophtheirus salmonis), while others, such as those belonging to the genus Caligus, are known to be more generalists [1, 2]. Caligus species can live in a wide range of environments [1, 2]. In Asia, several species of Caligus sea lice, including Caligus epidemicus, C. chiastos, C. punctatus, C. multispinosus, and C. rotundigenitalis have been reported to infect farmed grouper [3,4,5]. In Hong Kong, which has a family-based marine aquaculture industry that produces ∼1,000 tons of fish per year (https://www.gov.hk/en/about/abouthk/factsheets/docs/agriculture.pdf) there have been anecdotal reports of unknown species of sea lice affecting farmed hybrid grouper

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Results