A review of potential pathogens of sea lice and the application of cleaner fish in biological control

Abstract

There are many examples of successful biological control of pest populations in aquatic environments. This approach to sea louse control has environmental benefits and is cost-effective. The range of possible pathogens of lice is reviewed and epibionts recorded from sea lice, including the monogenean Udonella caligorum and ciliates, are examined. Baculoviruses when ingested by insects form occlusion bodies resulting in severe damage to the digestive system and subsequent death, and this may be a promising approach. Cleaner wrasse (Labridae) have been stocked commercially with farmed salmon since 1989, and recent work on improving the method is reviewed. Wrasse are sourced from a wild fishery and stocked at ratios of 1 to 25-150 salmon. Over 5 million wrasse are stocked annually in Norway and c 30% of smolts in Scotland were stocked with wrasse until 1998, when an outbreak of infections salmon anaemia (ISA) deterred many farmers from transferring wild fish to cages. A case study is given showing that salmon in cages stocked with wrasse had a burden of one to eight lice through the first year compared with up to 40 lice per fish on unprotected and untreated fish. Electivity indices were used to compare the relative composition of lice developmental stages on salmon in stocked and unstocked cages, and adult male and female lice were found to comprise only 6% of the population in cages with wrasse, compared with 49% adults on fish in control cages. Measures to improve the efficacy of wrasse as a way of cleaning salmon in the second production year include the use of refuges to assist over-wintering survival, and stocking ballan wrasse. Health hygiene includes sourcing wrasse in the farm locality, testing for pathogens, vaccination of wrasse and ultimately rearing wrasse for stocking. The role of wrasse in an IPM strategy is described.

Population biology of infectious diseases shared by wild and farmed fish

“…Furthermore, knowledge from food web ecology has helped identify and implement parasite control systems that include the co-stocking of cleaner fish, which consume parasites on farmed fish, as well as multitrophic aquaculture systems where filter feeders utilize the waste from finfish farms and kelp utilize the nutrient enrichment from both finfish and filter feeders (Mordue and Pike 2002;Treasurer 2002). Domesticated fish populations have also become more resistant to disease outbreaks via selective breeding as well as improved husbandry and site selection that reduce sources of stress that can make fish more prone to disease (Pohlenz and Gatlin 2014;Ellis et al 2016;Naslund and Johnsson 2016).…”

The effect of temperature and fish size on growth of juvenile lumpfish (Cyclopterus lumpus L.)

“…The biological control of sea lice through the use of "cleaner fish" has recently become a feasible option due to the increased occurrence of resistant lice, the reduced public acceptance of the use of chemotherapeutants in food production and the urgent need for an effective and sustainable method of parasite control in Atlantic salmon aquaculture (Denholm et al, 2002;Treasurer, 2002). Today cleaner-fish present the only environmentally friendly alternative to chemical de-lousing of salmonids (Cowx et al 1998;Treasurer 2002).…”

“…Today cleaner-fish present the only environmentally friendly alternative to chemical de-lousing of salmonids (Cowx et al 1998;Treasurer 2002). Their use has a lower impact on the environment, reduces cortisol levels of farmed fish, and is often found to be a cheaper alternative to chemical treatments (Treasurer 2002).…”

“…Today cleaner-fish present the only environmentally friendly alternative to chemical de-lousing of salmonids (Cowx et al 1998;Treasurer 2002). Their use has a lower impact on the environment, reduces cortisol levels of farmed fish, and is often found to be a cheaper alternative to chemical treatments (Treasurer 2002). Cleaner fish have been utilized as a predator of sea louse in salmon net pens for several years, efficiently grazing on ectoparasites; mobile pre-adult and adult lice (Groner et al 2013).…”

Polysiphonia spp as epibiont of Caligus rogercresseyi (Crustacea: Copepoda) in Salmo salar farming centers

“…Treasurer (2002) and Jones and Beamish (2011) have described for this parasite the presence of the alga Ulva spp, some ciliated protozoans and monogeneans of the Udonella genus.…”