Date of Award
Program or Major
Master of Science
Elizabeth A Fairchild
Sea lice are copepodid ectoparasites that infect fish, and cost salmonid farmers millions of dollars each year in damaged product and mitigation efforts. Conventional treatments can unintentionally impact the ambient environment and lead to the lice developing resistance to the treatments. In recent years, lumpfish (Cyclopterus lumpus) have been utilized successfully to naturally clean sea lice from infected salmonids in European and Atlantic Canadian farms, however this technology has yet to be used in US farms. In New Hampshire coastal waters, New Hampshire Sea Grant and the University of New Hampshire operate an experimental steelhead trout (Oncorhynchus mykiss) farm, AquaFort. To understand seasonal occurrence of lice populations at AquaFort and which lice species are present, steelhead were subsampled weekly for sea lice during farm use throughout 2019-2021. Lice abundance, species present, sex ratio, life stage, and occurrence of gravid females were determined. Lice loads (mean lice per fish) peaked on January 19, 2020, at 3.60 lice per fish, and the dominant species observed was Caligus elongatus (n=930) though some individuals of Caligus curtus were observed (n=9). Female lice made up 74% of the lice population throughout the assessment, and adults made up 87% of all lice observed throughout the assessment. The lice loads of gravid females peaked on February 18, 2021, at 2.20 gravid lice per fish. To understand how lumpfish could mitigate sea lice infestations, small, in situ- experimental cages were stocked with different treatments of steelhead trout (strain), lumpfish (presence, absence), and lumpfish hide designs (kelp, PVC panels). Water temperature, fish survival, lice loads, and lumpfish stomach contents were analyzed throughout two 5-week trials to examine lumpfish impacts on sea lice loads. In both caging trials, hide design affected mean lice loads on trout, with lower lice loads in cages containing kelp hides, and in one trial, lice loads were lower in cages containing lumpfish versus no cleanerfish, however, there was no evidence of sea lice within lumpfish stomachs at the end of each trial. Water temperature and lumpfish size differed between the two trials suggesting that cleanerfish size, hide design, and water temperature are key variables to consider for effective sea lice control. These foundational studies contribute towards developing best practices of lumpfish use for sea lice mitigation on steelhead trout, such as when to implement lumpfish to maximize their welfare and cleaning capabilities. This will ultimately lead towards the goal of increasing the sustainability and production of steelhead trout aquaculture in NH coastal waters.
Doherty, Michael Brian, "THE PRESENCE OF SEA LICE ON STEELHEAD TROUT AT A MARINE FARM IN NH WATERS AND THE UTILIZATION OF LUMPFISH AS A BIOLOGICAL DELOUSER" (2021). Master's Theses and Capstones. 1504.