Using cleanerfish for sea lice biocontrol is becoming a common practice in salmonid aquaculture in the North Atlantic, however, it has yet to be implemented in the US and there is still much to learn. At the University of New Hampshire (UNH), lumpfish (Cyclopterus lumpus) cleaning behaviors are being assessed with steelhead trout (Oncorhynchus mykiss), a salmonid important to the future of New Hampshire’s finfish aquaculture industry.
In 2020 and 2021, we utilized an experimental steelhead trout aquaculture pen off the NH coast, operated by NH Sea Grant and UNH. Weekly from November to June, we assessed sea lice populations collected from a subsample of steelhead trout and documented lice species, life history stage, sex, and abundance. Lice loads (mean lice per fish) peaked in January 2020 at 3.60 lice per fish, and the dominant species observed was Caligus elongatus (99%; n=930) though some individuals of Caligus curtus were observed (n=9). Female lice and adult lice made up 74% and 87% of the lice population, respectively, throughout the assessment. The lice loads of gravid females peaked in February 2021 at 2.20 gravid lice per fish.
Using small microcosm cages stocked with steelhead trout, we also evaluated whether lumpfish presence and hide design (fake kelp, PVC panels) affected sea lice loads. Two 10-week trials were conducted from October to December 2020, with all fish sampled biweekly for lice. At the end of each trial, all lumpfish were euthanized, and gut contents analyzed. Hide design affected mean lice loads on trout in both trials, with lower lice loads in cages containing kelp hides (Trial 1: GLM, p=0.01; Trial 2: GLM, p=0.02). Lice loads were lower in cages containing lumpfish versus no cleanerfish (GLM, p=0.04), but only in one trial. There was no evidence of sea lice within any lumpfish stomachs. Water temperature and lumpfish size differed between the two trials suggesting that cleanerfish size, hide design, and water temperature are key variables for steelhead farmers 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 waters.