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 NH coastal waters, NH Sea Grant and UNH operate an experimental steelhead trout farm, AquaFort. To understand seasonal occurrence of lice populations at AquaFort and when lumpfish use would be most effective, trout 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. To understand how lumpfish could mitigate sea lice infestations, smaller (785 L) experimental cages were stocked with different treatments of steelhead trout, lumpfish, and lumpfish hide designs. Water temperature, fish mortality, lice loads, and lumpfish stomach contents were analyzed during two 5-week trials to examine lumpfish impacts on sea lice loads. In both trials, there were significantly different mean lice loads on trout between the hide designs, though no evidence of sea lice was observed in lumpfish stomach content analysis. One trial displayed significantly different mean lice loads between lumpfish and trout. These results suggest that lumpfish size, trout strain, hide design, and water temperature act as variables to consider for effective sea lice control. These foundational studies contribute towards developing best practices of lumpfish use for sea lice mitigation, leading towards the goal of increasing the sustainability and production of steelhead trout aquaculture in NH.
