The development of the Norwegian wrasse fishery and the use of wrasses as cleaner fish in the salmon aquaculture industry

Norway leads the world aquaculture production of Atlantic salmon Salmo salar and farmed Norwegian Atlantic salmon is currently consumed around the globe. However, sea lice infestation is a major problem faced by the salmon aquaculture industry in Norway and elsewhere. The use of wild-caught cleaner fish, mainly wrasses, has been recommended over the other available methods as the most economical and environmentally friendly option to control sea lice infestation in salmon farming. Here, we review the development of the Norwegian wrasse fishery and the use of wrasses as cleaner fish. In this document, we address the sea lice problem and introduce the main wrasse species employed as cleaner fish, document the cleaning behaviour of wrasses, present the development of a new wrasse fishery associated with the salmon aquaculture industry, and finally, we identify the main challenges associated with the intensive use of wild-caught cleaner wrasses and provide some insight for future directions of the wrasse fishery and further development of aquaculture techniques to supply salmon facilities with domesticated cleaner fish.     

Salmon lice infection of wild sea trout and Arctic char in marine and freshwaters: the effects of salmon farms

The abundance of salmon lice and the physiological effects of infection were examined in two stocks of sympatric sea trout and anadromous Arctic char in northern Norway. One stock feed in a coastal area with extensive salmon farming (exposed locality), while the other feed in a region with little farming activity (unexposed locality). The results showed that the lice infection was significantly higher at the exposed locality, at which the mean intensity of infection peaked in June and July at over 100 and 200 lice larvae per fish respectively. At the exposed locality we also observed a premature return to freshwater of the most heavily infected fish. Such behaviour has previously been interpreted as a response by the fish to reduce the stress caused by the infection and/or to enhance survival. Blood samples taken from sea trout at sea at the exposed locality showed a positive correlation between intensity of parasite infection and an increase in the plasma cortisol, chloride and blood glucose concentrations, while the correlations from sea trout in freshwater were more casual. Several indices pointed towards an excessive mortality of the heaviest infected fish, and 47% of the fish caught in freshwater and 32% of those captured at sea carried lice at intensities above the level that has been shown to induce mortality in laboratory experiments. Furthermore, almost half of all fish from the exposed locality had lice intensities that would probably cause osmoregulatory imbalance. High salmon lice infections may therefore have profound negative effects upon wild populations of sea trout. At the unexposed location, the infection intensities were low, and few fish carried more than 10 lice. These are probably within the normal range of natural infection and such intensities are not expected to affect the stock negatively.     

Approaches for controlling sea lice infestation in global salmon farming: What is applicable in Canadian aquaculture industry

ABSTRACT

This article describes the sea lice control methods that are currently applicable to salmon farming in Canada. Three commercial chemical products are approved for use against sea lice in Canada: Slice®, Interox® Paramove® 50, and Calicide®. Physical control methods include photoperiod and cage-depth manipulations, desiccation of farm equipment, and the use of electric fences. Biological control measures include the polyculture of salmon with wrasse or mussel. Nutraceuticals and immunostimulants shown to reduce sea lice infestations in salmon include unmethylated DNA, yeast fermentation extract-Brewer’s yeast compound, AllBrew and NuPro, MacroGard®, and Optimûn®. Salmon farmers are recommended to use site-specific integrated approaches, by properly adapting a combination of chemical, physical, biological, and nutritional measures to the environmental and financial characteristics of their farm. In the future, development of vaccines against sea lice and of salmon lines resistant to sea lice will play a pivotal role in fighting against this parasite.     

Where art thou louse? A snapshot of attachment location preferences in salmon lice on Atlantic salmon hosts in sea cages

Problematic sea lice infestations on farmed Atlantic salmon (Salmo salar) have motivated extensive research and development into new methods to prevent, monitor and control sea lice. Most of these technologies require detailed information on the behaviour, spatial distribution and demography of lice on host fish. This study investigated how salmon lice (Lepeophtheirus salmonis) infestation density varies across the host's surface under sea cage farming conditions. Lice abundance, demography and attachment location were tracked over time, with repeated sampling of 300 individually tagged salmon across three replicate experimental sea cages. The data reveal clear differences in attachment locations according to sex and stage, but with an overall preference for the dorsal surface among mobile stages—dorsal head for adult females and dorsal-posterior section for males and pre-adults. Total lice abundance was highly variable between repeated measures of individual fish, consistent with frequent host-switching or mortality. Total lice numbers also declined between sampling dates, likely due to handling, with lost mobile lice being almost exclusively adult males. As the distribution of sea lice on hosts is likely determined by numerous factors, future image-based automated detection systems should be validated in settings that reflect the complex host–parasite interactions that occur in open farming systems.     

Technology for cultivation of Atlantic salmon, Salmo salar L.: problems and possibilities

Abstract. The concept of farming Atlantic salmon, Salmo salar L., beyond smolt stage in sea water started in Norway and Scotland in 1967–1968, using natural enclosures or sea water ponds. Cage culture has since 1969 developed to be the dominating method. Atlantic salmon is cultivated in more than nine countries with a production of 235400t in 1990. Incubation of eggs, hatching, first feeding and smolt production have to a large degree been standardized. Various types of incubator systems and holding units are briefly presented and discussed. There has recently been a trend to move ongrowing cage farms from inshore and sheltered waters to more open and offshore locations. The various types of cages and supplemental equipment for the two options are compared and evaluated. The offshore trend is a more expensive and difficult technology than existing inshore farming methods. Sea enclosures and net enclosures are less attractive. There is new interest in pump ashore systems. Large land-based farms have been built in six countries with varying success. The amounts of water required are enormous and constructions costs are high, but running costs are comparable to cage culture. Great improvements have taken place for both smolt farms and pump ashore farms in treatment of water, use of heat exchangers, filtration of water, disinfection, aeration, oxygenation, photoperiod and light control, automatic feeding, internal transport, handling of fish and surveillance and control systems for fish and water. The problems and prospects of farming are discussed in relation to new and old technology.     

Evaluation of sea lice abundance levels on farmed Atlantic salmon (Salmo salar L.) located in the Broughton Archipelago of British Columbia from 2003 to 2005

Salmon farming began in British Columbia (BC) in the 1970s and in 2006, aquaculture represented BC's largest agricultural export. Along with this growth in production has been a growth in controversy, including the concern that sea lice originating from Atlantic salmon farms negatively impact wild juvenile pink salmon in the Broughton Archipelago. To understand the dynamic interaction between wild and farmed fish, data for on‐farm abundance of sea lice are required. In this study, 33 000 Atlantic salmon from 20 active farms were examined over 3 years. Two species of lice were found: Lepeophtheirus salmonis and Caligus clemensi. Inter‐annual and seasonal variations in abundance levels occurred with lower levels of L. salmonis in 2003 compared with 2004 and 2005, while C. clemensi levels were highest in 2003. The abundance of L. salmonis was greater on older farmed fish. The findings are compared with European and eastern Canadian sea lice reports, and possible sources of sea lice on farmed salmon are discussed.     

Challenges and emerging technical solutions in on-growing salmon farming

Farming of Atlantic salmon has grown rapidly from its start in the early 1970s until today, with production approaching two million tonnes. Sea cages are the dominant production system for the on-growing stage of salmon farming. It represents an effective production system with lower investment and running costs than land-based systems. The development and improvement of the sea cage farming system has been one of the most important factors for the growth of the salmon farming industry. However, during recent years certain problems related to their placement in the open marine environment have proved highly challenging, increasing operating costs and impacting on industry public relations. The problems are mainly due to parasites, diseases and escape of fish. In this article, emerging technical solutions for solving those problems are described.     

A note on sea lice abundance on farmed Atlantic salmon in Scotland 2011–2013: significant regional and seasonal variation

Sea lice are the most economically damaging parasite affecting marine Atlantic salmon production the dominant sector of UK aquaculture. The Scottish Salmon Producers' Organisation has published mean adult female lice abundance for four regions for 2011–2013 and for 30 areas in 2013. An analysis of these data shows that sea lice abundance is highly seasonal with values lowest in the first half of the year. Abundance also varies by region, the regional patterns vary from year‐to‐year but overall the highest abundance was found in the northern part of mainland Scotland. While most areas had low lice abundance, in a few areas the abundance was persistently above average; these areas were clustered together. There was no significant year‐on‐year trend in lice abundance, and trends appear to vary between regions. Although previous Scottish analyses have been carried out using data from a large company, this analysis cover 95% of production in all salmon farming regions of Scotland and it can be extended as more data become available.     

How are the salmon lice (Lepeophtheirus salmonis Krøyer, 1837) in Atlantic salmon farming affected by different control efforts: A case study of an intensive production area with coordinated production cycles and changing delousing practices in 2013–2018

The aims of the present study were to describe the salmon lice (Lepeophtheirus salmonis Krøyer, 1837) situation in an intensive salmon production area in mid‐Norway and to consider implications of changing practices of how salmon lice infestation can be controlled. The results in this study suggest that there are steps that can be carried out to keep salmon lice under control even during years when the temperature facilitates a quick salmon lice development. The present work indicates that the use of cleaner fish can delay the time it takes adult female lice to reach 0.1 per salmon in the beginning of a production cycle. It suggests that the timing of cleaner fish deployment into salmon cages can influence its effectiveness in controlling salmon lice. It also gives caution to letting salmon lice develop unchecked, even at levels far below the current lice limit, because of the difficulties to control salmon lice when the external infection pressure is too high. This study took place during a rapid change in delousing methods, in an area with coordinated salmon production. Despite its exploratory nature, this study offers insights into the salmon lice fluctuations in relation to efforts aimed at controlling it.     

Sea lice treatments, management practices and sea lice sampling methods on Atlantic salmon farms in the Bay of Fundy, New Brunswick, Canada

Proper monitoring of all stages of sea lice is imperative to ensure the strategic timing of treatments. Although sea lice receive close attention and management for production purposes, there are no regulations for the reporting of lice burdens on salmon farms in Atlantic Canada, nor are there officially standardized protocols for conducting sea lice counts in the field. The purpose of this study was to complete a survey of Atlantic salmon farms in the Bay of Fundy, NB, Canada. The survey addressed many aspects of sea lice monitoring and control, including methods for sea lice sampling at the site, types of treatments administered for control of sea lice and management practices and decisions regarding the control of sea lice. A total of 83 surveys were completed from July to December 2002. Twelve of the 60 respondents owned and/or operated more than one site and completed a survey for each of their sites at the time of the interview. The position of individuals surveyed included 48 site managers (representing 63 sites), three site owners (representing 11 sites), eight individuals who were both owner and manager (representing nine sites) and one site veterinarian (representing one site). Surveys were completed on 30 sites from the Limekiln Bay and surrounding areas, 23 sites from Grand Manan Island, 18 sites from Deer Island, six sites from Campobello Island and six sites from Passamaquoddy Bay. Fish farmers, in concert with their veterinarians, generally perform intensive monitoring and control practices. However, there is a continued reliance on emamectin benzoate (SLICE^®) for sea lice control on Atlantic salmon farms in the Bay of Fundy, which raises concerns regarding the potential for sea lice to develop resistance to the drug.     

Caligus elongatus Nordmann genotypes on wild and farmed fish

Two mitochondrial genotypes have been described for Caligus elongatus Nordmann in Norway. This article reports on the distribution of C. elongatus mitochondrial cytochrome C oxidase 1 genotypes from wild fish hosts from the SE Norwegian coast. For comparison, lice from areas with fish farming were included in the study. The genotype distribution of 841 lice from wild coastal (n = 535), wild North Sea pelagic (n = 26), farmed (n = 160) and wild hosts in areas of fish farming (n = 89) is presented. The genotype frequencies of C. elongatus on wild coastal hosts varied significantly between spring and autumn. Lice from these fish show a large proportion of genotype 1 lice in March-June every year. Genotype 2 lice were found more frequently in autumn. Genotype 1 was clearly associated with the lumpfish, Cyclopterus lumpus L. The genotype frequency appeared to be different in areas with aquaculture. Caligus elongatus from farmed fish and wild fish caught close to Atlantic salmon fish farms in Norway were predominantly genotype 1 in autumn. Genotypes of C. elongatus on the SE coast of Norway vary according to season and fish species. Factors involved in the encounter between fish and lice are important for the establishment of lice on their hosts.     

The competitiveness of the Chilean salmon aquaculture industry

Abstract

Commercial salmon and trout farming has emerged as a major industry in Chile during the 1990s. Salmon is not a native species to Chile, still excellent climatic conditions are provided for farming. Since 1992 Chile has been the second largest producer of farmed salmon and trout in the world after Norway. This report reviews the development of the Chilean salmonid industry from its early stages until today with respect to production patterns, legislation and main markets. A cost comparison between Chilean and Norwegian farmed salmon is also provided. Finally, the international competitiveness and future challenges of the Chilean salmonid farming industry are analysed.     

Detection and classification of Lepeophterius salmonis (Krøyer, 1837) using underwater hyperspectral imaging

Salmon louse, or sea lice, (Lepoptherius salmonis) represents practical, economical and fish welfare challenges for salmon farming (Hamre et al., 2013) and for the free-living stocks of salmon. There is an urgent need in the industry for a system that provides reliable numbers of louse on farmed salmon. Underwater hyperspectral imaging represents a potential new technique for louse counting in sea cages. In laboratory studies, the UHI technology could detect and classify pre-adults (pre-adult I and II), adult males and adult females (ovigerous) of sea lice based on the difference in their spectral characteristics. A model was built for detection of lice on the salmon and the UHI had a detection success ranging from 67 to 100 % with an average of 82%. A classification of the detected lice was performed for pre-adults, adult males and ovigerous lice and had a prediction accuracy of 85% when lice were divided into three groups (pre-adults, adult male and ovigerous lice) and 93% when lice were divided in two groups, ovigerous lice and all the other mobile lice (pre-adults and adult male). An automatic procedure for in situ measurements of louse infected salmon could deliver a data basis several times higher than the traditional counting system. The next generation of UHI louse detector should be developed with a higher spatial resolution to be able to detect also the sessile stages of lice. For succeeding with in situ classification of L. salmonis, correction algorithms to compensate for the impact of water between the UHI and lice need also to be developed.     

A closer look at closed cages: Growth and mortality rates during production of post-smolt Atlantic salmon in marine closed confinement systems

The most controversial environmental problems in commercial salmon farming are the negative effects of sea lice (Lepeoptheirus salmonis, Caligus spp.), the genetic introgression of farmed salmon in wild populations, nutrient waste load and the emission of potentially toxic waste to coastal waters. Moving production from sea cages to land-based facilities, offshore farming or marine closed containment systems (CCS) are suggested as possible ways to solve these problems. However, there are few published studies on production capacity and fish welfare in such systems. The main aim of this study was to describe growth rates, mortality rates and mortality causes in the commercial-scale production of Atlantic salmon (Salmo salar) post-smolts in CCS from sea transfer until the size of 1000 g. From October 2014 to May 2017, we recorded growth rates, feed use, mortality and mortality causes during 23 CCS production cycles, including 18 CCS periods with off-season smolt (S0) and 5 CCS periods with one-year smolt (S1). The mean (SD) growth rate, thermal growth coefficient (TGC), for all 23 CCS was 3.03 (0.34), with no difference between cages with S1 (n = 5) and cages with S0 (n = 1 8). Cumulative mortality three months after sea transfer (CM_3mo) was 2.6 %, while cumulated mortality throughout the total trial period (CM_total, mean number of days = 159) was 3.6 %. Both CM_3mo and CM_total were higher in S1 groups than in S0 groups. Mean (SD) feed conversion ratio in CCS with S0 (n = 18) was 1.11 (0.07). The two main mortality causes were ‘Ulcers and fin rot’ (S1 and S0) and ‘Failed smolt’ (S1), accounting for 36.1 % and 19.3 % of the total mortality, respectively. Water flow, oxygen saturation and other water quality parameters were within safe limits for fish health and welfare.     

Catch me if you can: How to recapture lumpfish using light as an attractant

The use of lumpfish in salmon farming allows the removal of sea lice all year round, without the use of chemicals or mechanical treatments. In Norway alone, around 31 million lumpfish are currently put into sea pens whereas no efficient method to re-catch these fish once they no longer are efficient salmon lice grazers (from 300 g) exists. At present, collecting lumpfish in sea-cages is a labour- and time-consuming process and, if these fish are to be harvested, an efficient method for collecting lumpfish is urgently needed. In this study, we tested coloured light as an attractant to lure lumpfish into passive traps (pods). Three small-scale pilot experiments both demonstrated the highest re-capture rate when a blue light-source was used, whereas red and yellow light gave the lowest re-capture rate. A subsequent large-scale trial failed to demonstrate significant re-catch of lumpfish. It is concluded that although blue light clearly attracted lumpfish in laboratory trials, further studies are needed in order to exploit this attribute commercially.     

Comparison of growth rate in Atlantic salmon,pink salmon,Arctic char,sea trout and rainbow trout under Norwegian farming conditions

Growth rates of Atlantic salmon, pink salmon, Arctic char, sea trout and rainbow trout were compared under Norwegian farming conditions. During the juvenile, freshwater period, growth was fastest in pink salmon, followed by rainbow trout and Arctic char. Freshwater growth of sea trout and, especially, Atlantic salmon, was slow. After transfer of smolts or fingerling to sea water, Arctic char failed to survive the autumn. Sea water growth of sea trout was slow, but the three species, rainbow trout, Atlantic salmon and pink salmon, all grew rapidly through all seasons. When in sea water, rainbow trout and pink salmon were regularly attacked by vibriosis, while Atlantic salmon were rarely attacked, and sea trout never. It is concluded that, for commercial farming in Norway, rainbow trout are of value for production of fish of any size up to 3–4 kg, and pink salmon for production of small fish of 0.5–1.5 kg. Atlantic salmon is the only species suitable for production of a very large salmonid, i.e., more than 4–5 kg.     

Distributions of planktonic sea lice larvae Lepeophtheirus salmonis in the inter-tidal zone in Loch Torridon, Western Scotland in relation to salmon farm production cycles

This study examines the relative density of sea lice, Lepeophtheirus salmonis (Krøyer), larvae in the inter‐tidal areas of Loch Torridon, a fjordic sea loch in Western Scotland and the site of several commercial salmon farms. Samples of planktonic sea lice were collected in each spring from 1999 to 2003 near the mouth of the River Shieldaig, where sea trout have been shown to congregate in the first few days after going to sea, and from 2001 to 2003 near the mouth of the River Balgy. No larval sea lice were found near the mouth of the River Shieldaig in spring 2000 or 2002, when gravid female sea lice were absent on local fish farms. The same finding was observed in 2002 at the mouth of the River Balgy. In springs of 1999, 2001 and 2003, peak densities of larval sea lice of 33, 94 and 143 m^?3, respectively, were observed at the mouth of the river Shieldaig. At the mouth of the River Balgy, peak densities of 74 and 78 lice m^?3 were observed in 2001 and 2003 respectively. At the time these samples were collected, the two local salmon farms were in the second year of their production cycle and gravid female sea lice were present. Samples of larval sea lice were also obtained year round, at approximately weekly intervals, from a 50‐m transect at the mouth of the River Shieldaig, from March 2001 to June 2003, and compared with frequencies of gravid female sea lice on the two local salmon farms. High levels were found in the winter. No planktonic sea lice were found in this transect when gravid females were not present on the local fish farms.     

Salmon aquaculture in Chile

Abstract

Commercial salmon and trout farming has emerged as a major industry in Chile during the last two decades. Salmon is not a native species to Chile; however, excellent climatic conditions are provided for farming activities in the southern part of the country. After negligible production volumes during the early years, the harvest levels accelerated in the late 1980s, and since 1992 Chile has been the second largest producer of farmed salmon and trout in the world after Norway. This report reviews the development of the Chilean salmonid industry from its early stages until today with respect to production patterns, legislation and main markets. A cost comparison between Chilean and Norwegian farmed salmon is also provided. Finally, the international competitiveness and future challenges of the Chilean salmonid farming industry are analysed.     

Early‐stage sea lice recruits on Atlantic salmon are freshwater sensitive

Sea lice are significant parasites of marine and brackish farmed fishes. Freshwater bathing is a potential control option against numerous sea lice species, although has been viewed as futile against those that are capable of tolerating freshwater for extended periods. By comparing freshwater survival times across host‐attached stages of Lepeophtheirus salmonis (Krøyer), a key parasite in Atlantic salmon farming, we show the first attached (copepodid) stage undergoes 96–100% mortality after 1 h in freshwater, whereas later attached stages can tolerate up to 8 days. Thus, regular freshwater bathing methods targeting the more susceptible attached copepodid stage may successfully treat against L. salmonis and potentially other sea lice on fish cultured in marine and brackish waters.     

Development of the use of wrasse to control sea lice on salmon farms in Ireland

Abstract. Developments in the use of wrasse as cleaner-fish in the control of sea lice ( Lepeophtheirus salmonis, Caligus elongatus ) in Ireland are reviewed. Corkwing, Symphodus melops , and goldsinny, Ctenolabrus rupestris , have controlled L. salmonis (<1 louse per salmon) on commercial farms. C. rupestris and rockcook, Centrolabrus exoletus , removed both adult and chalimus C. elongatus in aquarium trials. No egg-bearing lice were ever found on salmon in cages with wrasse, and numbers of mobile lice were maintained at <1 per salmon smolt.
Wrasse are fished using shrimp pots, optimally set for about 2 h. The fishery is seasonal and limited to >10cm wrasse occurring close to the farm, and distant from other farms. Localized reductions in the body length and numbers of wrasse have been detected in the second year of fishing in two areas respectively. Due to the fishery limitations and high fecundity of wrasse, impacts on wrasse populations should remain localized. All wrasse populations fished are screened for microbial diseases, and protozoan and metazoan parasites. Results are typical for wild marine fish but metazoan skin parasites are rare. No pathogens, including tests with an Aeromonas sp. found in wrasse, have been found to be transferable to salmon.
Wrasse are the only effective and continuous method of sea lice control legally available. Research efforts should be directed towards improving the availability, pathogen-free status, and husbandry of wrasse, to enable cleaner-fish technology to be more widely and efficiently utilized.