In the Press: Efficacy of cleaner fish as biological control agents
Tens of millions of cleaner fish (multiple species of wrasse and lumpfish) are stocked by Norwegian salmon farmers each year to biologically control the industry’s most pesky parasite: salmon lice. It is one of the only farm management practices we are aware of where a vertebrate is used to control a pest of the other vertebrate. Their use in farms is unsurprisingly controversial, especially as there are multiple reports that high mortality rates for these cleaner fish stocked in the sea cages are a common occurrence.
With this in mind, last year, members of our lab delved into the existing literature to look at what existing evidence base is for how effective these cleaner fishes are at delousing, and this review was published in Aquaculture Environment Interactions. We found that:
- The reported effect of cleaner fish on the number of salmon lice on salmon in the different studies varied greatly.
- Only 11 published studies had examined lice predation in experimental setups with and without cleaner fish and in general replication was low,
- Almost all studies were done in small experimental cages or tanks and only one published study was performed in large, commercial-sized cages.
We then also decided to conduct a ‘big data’ analysis using publicly available data to investigate the efficacy of cleaner fish deployed in Norwegian salmon farms in Norway for sea lice control, which was published in the International Journal for Parasitology. Our analysis revealed that effects were unreliable and patchy, and while some farms show good results from cleaner fish, these effects usually lasted less than 3-5 months, and there are nearly as many farms where cleaner fish do not seem to work at all.