the Fish Site
18 April 2017, at 1:00am
Following the successful deployment of a number of species notably lumpsuckers and ballan wrasse as cleanerfish in salmon cages in the eastern Atlantic, the aquaculture industry in BC has been seeking to find a fish native to the Pacific that might be able to pick lice off its salmon.
And, 18 months in to the project – the first of its kind in BC – Dr Shannon Balfry, from the BC Centre for Aquatic Health Sciences, tells The Fish Site that it has already yielded some promising results.
What inspired the current cleanerfish project?
In BC, the public and various eNGOs have expressed concern over the potential spread of sea lice from farmed to wild salmon. The use of cleanerfish to manage sea lice on salmon farms – which has been shown to be successful in other salmon farming nations such as Norway and Scotland – is an environmentally friendly solution to this issue, which can also generate positive economic impacts for the salmon sector because it can lessen the need for costly medicinal treatments.
How did you decide on which species to use in your trials?
Local BC coastal waters do not have wrasse or lumpfish, but there are reports in the literature of cleaning behavior being observed by both kelp perch (Brachyistius frenatus) and pile perch (Rhacochilus vacca). Analysis of guts from wild kelp perch have revealed parasitic copepods, isopod larvae and fish scales, which supports the observations made of cleaning behavior.
How have you conducted the trials to date?
Our initial research proposal outlined a series of 3 trials aimed at determining if kelp and/or pile perch would clean sea lice (Lepeophtheirus salmonis) off infested salmon in experimental tanks, and if there were differences in cleaning activity between the two species of perch and between different sizes of the perch. In addition, we were looking for cleaning preferences in terms of sea lice life history stage, location of the lice on salmon, and cleaning behavior in the tank.
Over the course of the last few months, we have developed an infection model that will result in juvenile Atlantic salmon carrying up to 15 pre-adult/adult sea lice, primarily located on the dorsal surface of the salmon. We count, stage and sex the lice on the salmon immediately before placing them in the experimental tanks with the perch. Most of our trials are terminated after 48 hours of cohabitation, at which point, we remove all the fish (salmon and perch) and examine them externally for lice. The shorter than expected time for the perch to clean the salmon of the lice has meant that rather than the 3 trials we originally planned, we have completed over a dozen trials to study the cleaning activity of these two perch species.
Our initial trials involved euthanizing the cleaner fish to examine GI tracts for the presence of sea lice, but this is no longer required. Currently we siphon the tanks and outflow mesh screens daily to remove feces, etc. which are examined under a microscope for lice. Digested lice appear as tissue-free exoskeletons, while lice that have not been digested (which have probably dropped off the salmon for other reasons) are darker, with tissue still attached to the exoskeleton. In this way, we can track the number of lice on the salmon at the start of a cohabitation trial, and compare this with the number remaining on the salmon, and the number we have collected from the daily siphoning of the tanks. We are now able to account for 100% of the lice – either digested by perch, undigested or still attached to salmon.
What observations have you made to date?
We have placed small video cameras in some of the cohabitation trials and found that cleaning activity starts within a few hours of cohabitation. The perch and salmon display classic cleaning behavior, whereby the salmon will remain still and sometimes tilt to one side, which allows the perch easier access to the lice. The perch tend to hover over the salmon and can be frequently seen swimming around the salmon looking for lice. Clear video evidence of cleaning activity of both perch species has been observed.
What key variables have you noticed so far?
Cleaning activity in both perch species is variable – some individuals clean, some don’t. However, we have found that non-cleaners in one trial can become cleaners in subsequent trials and the source of this variability will be the focus of future research. So far we have not noted significant differences in cleaning activity between the two species. Appetite does not appear to impact cleaning activity either – perch starved for a couple days prior to introduction clean as well as fed perch. Smaller perch, of both species, appear to exhibit more cleaning activity than larger perch, and both species appear to have better appetite for larger female sea lice (probably because they are more visible).
The perch do not appear to ‘hurt’ the salmon by cleaning them. Though sometimes they will pick scales off salmon, we have not seen any wounds, etc.
How do you see the project evolving?
We plan to scale up the lab studies so we can use bigger tanks, bigger (and more) salmon, to answer questions such as the optimal stocking ratio of salmon to perch. In time this will allow us to establish field trials using salmon and perch in experimental net pens.
We also need to look into developing farming practices for the perch, as they cannot be sustainably harvested from the wild, in the long term. As a result, we need to develop breeding programs and hatcheries to produce perch for farms; develop formulated feeds for all life history stages of the perch; and conduct studies to understand potential disease issues.
Who has been involved in the project?
This has been a collaborative research projects with local salmon farmers Marine Harvest, Grieg Seafood and Cermaq; the BC Centre for Aquatic Health Sciences; and Fisheries and Oceans Canada. The lab studies are being conducted at the government laboratory, DFO Centre for Aquaculture and Environmental Research in West Vancouver, BC.
The Research has been funded by grants from the Marine Environmental Research Program of the BC Salmon Farmers’ Association, and SeaPact (a North American sustainable seafood organization).