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Improving sea lice grazing of lumpfish (Cyclopterus lumpus L.) by feeding live feeds prior to transfer to Atlantic salmon (Salmo salar L.) net-pens
Abstract
Two groups of PIT-tagged lumpfish (initial mean weight ± SD, 22.3 ± 2.5 g) were established in land-based tanks. One group received marine pelleted feed (MF group) whilst the other received a mix of pelleted feed, live adult Artemia and frozen sea lice (LF group), both groups with a feeding rate of 2% body weight⁻¹ per day for a period of 122 days. After this period 60 lumpfish (mean weight ± SD, 118.1 ± 7.7 g) mean from each group were Floy-tagged and transferred to four 5 × 5 × 5 m sea-pens containing 300 Atlantic salmon (mean weight ± SD, 668.4 ± 13.9 g), 30 lumpfish in each replicate sea pen. Two sea pens containing salmon only acted as controls. The sea pen study period lasted for 62 days. Individual weights and behaviour of the lumpfish were recorded every other week throughout the study period. In addition, regular lice counts were done, and the salmon were bulk-weighed at the start and end of the study period. Lower average numbers of female lice, pre-adult and combined pre-adult and mature male lice were recorded on the salmon in the presence of lumpfish from the LF group compared to lumpfish from the MF group. The behaviour of the two groups of lumpfish differed, as lumpfish from the LF group were more predisposed in locating natural food sources than fish from the MF group. The present study suggests that lumpfish exposed to live Artemia and frozen sea lice are more efficient in reducing lice counts on salmon after transfer to sea-pens.
... Imsland et al. [34] established two groups of individually tagged lumpfish in landbased tanks. One group received marine pelleted feed (MF group) whilst the other received a mix of pelleted feed, live adult Artemia, and frozen sea lice (LF group). ...
... Surprisingly, a positive association between the prevalence of organisms associated with biofouling and sea lice was found, indicating, that the occurrence of alternative food opportunities, in the form of biofouling organisms, had a positive influence on the cleaning efficacy of lumpfish. It was speculated that biofouling and the associated organisms stimulate a more active foraging behavior, which is supported by the data from [34] showing that live feed habituation stimulates sea lice grazing rate and efficacy of lumpfish. Data from Norway [10] indicate that lumpfish favor zooplankton as prey when it is available, reducing the sea lice grazing efficacy in periods with a large natural occurrence of zooplankton in sea pens, i.e., during summer. ...
... These results suggest that lumpfish fed live feed (here Artemia and frozen sea lice) prior to transfer to sea pens consumed more sea lice compared to the marine feed group. Imsland et al. [34] observed the behavior of the lumpfish at regular intervals during the study. Significant differences were detected between lumpfish fed only on marine dry feed during the juvenile stage (MF) versus lumpfish fed with a combination of dry and live feed (LF). ...
In this review, we have systematized current knowledge about the effect of stocking lumpfish (Cyclopterus lumpus) as cleaner fish to control Lepeophtheirus salmonis infestations on farmed Atlantic salmon (Salmo salar L.). The review was prompted by recent reports in which the usefulness of lumpfish has been doubted, and the urgent need to investigate whether common lumpfish can be used to reduce L. salmonis numbers on farmed Atlantic salmon by active grazing on this species. Available published data clearly indicate that lumpfish graze on L. salmonis, and can significantly lower the lice burden in Atlantic salmon farming. It is possible to enhance the lice grazing behavior of lumpfish with the assistance of live feed conditioning prior to sea pen transfer, and with selective breeding. Data indicate that lice grazing of lumpfish is size dependent, and grazing effect is low for lumpfish larger than 200–250 g. Observations from large-scale rearing of Atlantic salmon in open sea cages in Norway, Iceland, the Faroe Islands, and Scotland also indicate that lumpfish can be effective in lowering infestations of L. salmonis on salmon. Overall, this present review reveals that lumpfish can actively contribute to lower numbers of L. salmonis on farmed Atlantic salmon.
... Before sea transfer, lumpfish are fed on standard pelleted feed, with no prior experience of foraging on lice on salmon. In a recent study by Imsland et al. (2019), lumpfish were habituated to frozen salmon lice as feed in tanks. After transfer to experimental scale sea cages with salmon, the salmon that were placed with the lice-habituated lumpfish had 23% less lice than salmon placed with lumpfish that were reared with standard feed Figure 1 An example of how behaviour could be incorporated into production management in the routine farm practice of size grading. ...
... Macaulay et al. (2020a) found that salmon, with previous experience of surface-based air domes in freshwater tanks, refilled their swim bladders at a submerged dome at sea more frequently than salmon that were reared in plain tanks. Similarly, the lumpfish that Imsland et al. (2019) acclimated to frozen lice as feed in tanks were more effective lice grazers after sea transfer. Both studies demonstrate that a behaviour learned early in life was transferred to a substantially different culture environment. ...
... However, habituation and conditioning to encourage learning could be used in various ways in aquaculture to develop new desirable behaviours in fish that improve welfare. These include familiarization with new farm technologies (Macaulay et al. 2020a) and improving parasite control by acclimating cleaner fish to lice as food (Gentry, 2018;Imsland et al. 2019). Certain positive conditioning regimes could be relatively easy to establish to improve welfare by conditioning fish to aversive elements of the farm environment. ...
An understanding of behaviour is used in zoos, laboratories and agriculture to reduce stressful aspects of the captive environment for animals. While fish are one of the most cultivated of all vertebrate groups, incorporating their behaviour into production management has proved elusive. Here, we evaluate the current evi- dence base relating to use of (i) innate behaviours of fish and (ii) their ability to learn new behaviours via human-mediated training or through social learning, in fish farms. Studies that tested habituation and conditioning (training) as a tool to improve welfare demonstrate positive effects for improving fish welfare and cop- ing capacity. However, methods solely reliant on innate behavioural responses to stimuli will always be imperfect, due to variation in individual responses which are often context dependent. To date, there has been no successful demonstration of social learning as a tool for aquaculture. While many experimental scale studies report promising results, few have translated to commercial scale, highlighting a mismatch between theoretical and practical use and cautions against extrapola- tion of results from small-scale studies to commercial situations. While some promising evidence exists that fish behaviour can be integrated into farm manage- ment, logistical and scale-related hurdles must be overcome before this can occur. We conclude that fish behaviour is an additional and currently under-researched resource that could be integrated into farm practices to improve production and welfare in industrial aquaculture.
... Live Feeds Prior to Transfer to Atlantic Salmon Net Pens: Effect on the Occurrence of C. elongatus Imsland et al. (2019) established two groups of individually tagged lumpfish in land-based tanks. One group received marine pelleted feed (MF group) whilst the other received a mix of pelleted feed, live adult Artemia and frozen sea lice (LF group). ...
... On day 62, there was significantly less C. elongatus found on salmon from LF group compared to the control (SNK post hoc test, P < 0.05) as there was 38% less C. elongatus found on salmon reared with LF lumpfish compared to MF lumpfish. In the study of Imsland et al. (2019), the level of C. elongatus was significantly different between control and LF groups, indicating that the dietary treatment influenced the ability of lumpfish to effectively forage on C. elongatus as lumpfish conditioned prior to sea pen rearing were nearly 40% more efficient in grazing C. elongatus compared to controls. These results provided further supports to previous studies which reported that lumpfish do graze on C. elongatus (Imsland et al., 2014a). ...
... Total average number of C. elongatus per Atlantic salmon recorded for each duplicate treatment during each of the sampling dates of the sea pen study carried out byImsland et al. (2019). Values are presented as means ± S.D. Mean values which do not share a letter are significantly different (ANOVA, SNK post hoc test, P < 0.05). ...
In this mini review, we systematized current knowledge about the number of Caligus elongatus on farmed Atlantic salmon in relation to the use of lumpfish as cleaner fish. The review was prompted by reports of an unusually large number of sea lice (C. elongatus) infestation of farmed salmon in northern Norway, Faroese Islands and Iceland and the urgent need to determine if common lumpfish can be used to reduce the number on farmed Atlantic salmon by actively grazing on sea lice. Available data from Norway clearly indicate that lumpfish grazes on C. elongatus, and it is possible to enhance this grazing with the assistances of live-feed conditioning prior to sea pen transfer and selective breeding. Observations from Iceland, Faroese Islands and Scotland also indicate that lumpfish can effectively lower infestations of C. elongatus on salmon. Overall, this mini review expresses that lumpfish can actively lower the number of C. elongatus on farmed Atlantic salmon.
... Lumpfish (Cyclopterus lumpus) has been utilized as a cleaner fish species to biocontrol sea lice (e.g., Lepeophtheirus salmonis) infestations in Atlantic salmon (Salmo salar) farms in Atlantic Canada, Iceland, the US, the UK, and Norway [1][2][3][4]. Lumpfish cultivation is becoming an emergent aquaculture industry in the North Atlantic region [2][3][4][5][6], since its utilization significantly reduces or eliminates the application of toxic chemotherapeutics [3]. ...
... Lumpfish (Cyclopterus lumpus) has been utilized as a cleaner fish species to biocontrol sea lice (e.g., Lepeophtheirus salmonis) infestations in Atlantic salmon (Salmo salar) farms in Atlantic Canada, Iceland, the US, the UK, and Norway [1][2][3][4]. Lumpfish cultivation is becoming an emergent aquaculture industry in the North Atlantic region [2][3][4][5][6], since its utilization significantly reduces or eliminates the application of toxic chemotherapeutics [3]. ...
Lumpfish is utilized as a cleaner fish to biocontrol sea-lice infestations in Atlantic salmon farms. Aeromonas salmonicida, a Gram-negative facultative intracellular pathogen, is the causative agent of furunculosis in several fish species, including lumpfish. In this study, lumpfish were intra-peritoneally injected with different doses of A. salmonicida to calculate the LD50. Samples of blood, head-kidney, spleen, and liver were collected at different time points to determine the infection kinetics. We determined that A. salmonicida LD50 is 10 2 CFU per dose. We found that the lumpfish head-kidney is the primary target organ of A. salmonicida. Triplicate biological samples were collected from head-kidney, spleen, and liver pre-infection and at 3-and 10-days post-infection for RNA-sequencing. The reference genome-guided transcriptome assembly resulted in 6246 differentially expressed genes. The de novo assembly resulted in 403,204 transcripts, which added 1307 novel genes not identified by the reference genome-guided transcriptome. Differential gene expression and gene ontology enrichment analyses suggested that A. salmonicida induces lethal infection in lumpfish by uncontrolled and detrimental blood coagulation, complement activation, inflammation , DNA damage, suppression of the adaptive immune system, and prevention of cytoskeleton formation.
... An individual's previous experiences can be used to accelerate learning in farm animals by reducing the amount of uncertainty and fear experienced when they encounter novel situations (Wechsler and Lea, 2007). Several studies have found that farmed fish have the capacity for behavioural adaptation (Bratland et al., 2010;Folkedal et al., 2018;Imsland et al., 2019;). For fish, research indicates that enrichment in the early rearing environment causes them to be more behaviourally plastic and quicker to learn compared to fish reared in plain environments (Braithwaite and Salvanes, 2005;Strand et al., 2010;Salvanes et al., 2013). ...
... In the dome tanks, salmon learned to alter their surface behaviour through acclimation. Habituation to specific stimuli has been demonstrated in farmed fish before (Bratland et al., 2010;Folkedal et al., 2018;Imsland et al., 2019;). Although initially having restricted sur face access may have been stressful during habituation in tanks, evidence indicates that individuals that experience early life stress can recover more quickly from stressors they experience later in life (Vindas et al., 2018). ...
Parasitic salmon lice (Lepeophtheirus salmonis) are a severe problem for the Atlantic salmon (Salmo salar) farming industry. To reduce infestations, sea-cages can be submerged, below the depth at which lice are most common, with an underwater air dome being provided to allow salmon to refill their swim bladder and maintain buoyancy. When first transferred to a submerged sea-cage from freshwater tanks, salmon must adapt quickly to refill at the air dome or else become negatively buoyant, which has adverse consequences for fish welfare. Here, we tested if salmon that were habituated to surface-based air domes in freshwater tanks (dome-experienced; n = 3 cages) would use a submerged dome at sea more frequently than salmon that were reared in standard tanks (dome-naïve; n = 3 cages). PIT tagging revealed that dome-experienced individuals used domes 2.5× more and refilled their swim bladders 3× more often than dome-naïve individuals. Relative echo strength, which is an indicator of swim bladder volume, was on average 22% higher for dome-experienced fish compared to dome-naïve fish. Here, we demonstrate how training farmed salmon can improve behavioural and welfare outcomes for animals under industrial production. These findings show that salmon can learn a behaviour in the freshwater phase of production and apply this learning after being transferred to the marine environment.
... Lumpfish are being used as "cleaner fish" at Atlantic salmon (Salmo salar) cage-sites as a control for sea lice (Lepeophtheirus salmonis; Coates et al., 2021;Imsland et al., 2014Imsland et al., , 2018Powell et al., 2018), one of the most serious production challenges for this valuable species. Several studies report that this species is effective in eating sea lice off the salmon, thus improving production at cage-sites and the salmon's health and welfare and limiting mortalities Eliasen et al., 2018;Imsland et al., 2014Imsland et al., , 2016Imsland et al., , 2018Imsland et al., , 2019Solveig et al., 2023). ...
Lumpfish (Cyclopterus lumpus) mortalities have been reported during the summer at some North Atlantic salmon cage‐sites where they serve as “cleaner fish.” To better understand this species' physiology and whether limitations in their metabolic capacity and thermal tolerance can explain this phenomenon, we compared the aerobic scope (AS) of 6°C‐acclimated lumpfish (~50 g and 8.8 cm in length at the beginning of experiments) when all individuals (N = 12) were given a chase to exhaustion, a critical swim speed (Ucrit) test, and a critical thermal maximum (CTMax) test (rate of warming 2°C h⁻¹). The Ucrit and CTMax of the lumpfish were 2.36 ± 0.08 body lengths per second and 20.6 ± 0.3°C. The AS of lumpfish was higher during the Ucrit test (206.4 ± 8.5 mg O2 kg⁻¹ h⁻¹) versus that measured in either the CTMax test or after the chase to exhaustion (141.0 ± 15.0 and 124.7 ± 15.5 mg O2 kg⁻¹ h⁻¹, respectively). Maximum metabolic rate (MMR), AS, and “realistic” AS (ASR) measured using the three different protocols were not significantly correlated, indicating that measurements of metabolic capacity using one of these methods cannot be used to estimate values that would be obtained using another method. Additional findings include that (1) the lumpfish's metabolic capacity is comparable to that of Atlantic cod, suggesting that they are not as “sluggish” as previously suggested in the literature, and (2) their CTMax (20.6°C when acclimated to 6°C), in combination with their recently determined ITMax (20.6°C when acclimated to 10°C), indicates that high sea‐cage temperatures are unlikely to be the primary cause of lumpfish mortalities at salmon sea‐cages during the summer.
... Fultons kondisjonsfaktor brukes ofte for rognkjeks (Imsland et al., 2014(Imsland et al., , 2018b(Imsland et al., , 2019Geitung et al., 2020), men den antar at fisken ikke endrer form når lengden øker -altså at den vokser isometrisk, noe som er ikke tilfellet for rognkjeks (Daborn and Gregory, 1983). Resultater fra Boissonnot et al. (2022a) viser i tillegg at Fultons kondisjonsfaktor ikke har noe sammenheng med fettinnhold i lever og kan derfor ikke brukes tilå vurdere ernaeringsstatus hos rognkjeks. ...
... Much research is devoted to reducing the duration of the freshwater stage of salmonids with low technology and low cost while ensuring high survival and growth rates in seawater (Rosengren et al., 2017;Sievers et al., 2018;Hines et al., 2019;Nemova et al., 2020;Suzuki et al., 2020). The culture of Salmonidae has considerably developed in terms of scale and distribution (Albert et al., 2019;Barrett et al., 2020;Hvas et al., 2021). Although the condition control of culture has been very mature in RAS and many studies about the environmental effects on fish performance have been conducted, only few studies have been reported on steelhead trout compared with other fish species (Ge et al., 2021;Salinas et al., 2022). ...
Light and temperature are necessary conditions for migratory fish. The assessment of fish physiology and behavior is important for identifying fish welfare, but also for the assessment of the optimal setting of recirculating aquaculture systems (RASs). This study aimed to explore the interactive effect of photoperiod and temperature on steelhead trout culture. Four treatments were set up with specific settings were as follows: a LP-LT group treated with 16L:8D and 12°C, a LP-HT group treated with 16L:8D and 16°C, a SP-LT group treated with 12L:12D and 12°C, and a SP-HT group treated with 12L:12D and 16°C. Growth performance, behavioral and physiological parameters were measured. Two indexes, locomotor activity and social interaction were used for behavioral analysis, and the results were applied to interpret the behavioral responses to the photoperiod and temperature stimulation in juveniles. The growth performances were significantly lower in treatments LP-LT and SP-LT. The treatment LP-HT had significantly higher growth performance than the other treatments, but no significant differences were noted in survival rate and coefficient of variation. The results of fish behavior indicated that the movement of juveniles should be primarily monitored at high temperatures or long photoperiods, and the state parameters should be primarily monitored at low temperatures or short photoperiods. The results of the physiological parameters showed that the recovery time from stress varied among different treatments. After 60 days of the experiment, superoxide dismutase and alanine aminotransferase dropped back to their initial level. The results of Na+-K+-ATPase showed that although the combined effect of photoperiod and temperature could advance the time of smoltification, it may result in poorer salt tolerance. Our findings underscore the importance of the interaction of photoperiod and temperature on steelhead trout culture. The outcome could provide guidance for the development of effective aquaculture systems.
... Recently, operational welfare indicators for lumpfish [15,16] have been published that can be used to define best-practice guides for better welfare and reduced mortality. For several years, Gifas in collaboration with Akvaplan-niva has conducted several large-scale and small-scale studies [1][2][3][4][10][11][12]15,[17][18][19][20][21][22][23]. In these experiments, the focus has been on grazing effect, but information on mortality and loss has also been systematically gathered, which is presented in this study. ...
Data from research and commercial use of lumpfish were collected from the research facilities of Gifas (Inndyr, Northern Norway, 67.0° N, 14.0° E). The data were sourced from 12 main lumpfish groups subdivided into 66 subgroups (N = 160,729) delivered to Gifas between 2013 and 2020 and used in cleaner-fish research in (a) land-based facilities, (b) small-scale, or (c) large-scale sea pens. The data were standardised and organised into three main headings. Firstly, background information included transfer time, point of origin, mean starting weight and population size on arrival. Other information included to which site the lumpfish were transferred, volume of cage/tank, whether in the presence of salmon or not, stocking density, days at each site and water quality parameters. Causes of mortality were recorded, when possible, for each group, along with calculated mortality rates, patterns, and analytical information, along with imaging where available. Results show that causes of mortality varied within and between research sites. For lumpfish in hatcheries as well as for those deployed at small-scale sea pens, the primary cause of mortality was identified as pathogenic, while for lumpfish deployed at large-scale sea pens, transporting, grading and mechanical delousing were the primary causes of mortality. The results indicate that more research is required to clarify best practices both in commercial hatcheries and salmon cages and further understanding on lumpfish biological requirements and stress physiology is necessary to develop better methods that safeguard lumpfish welfare and meet their needs.
... Recently, biocontrol strategies have gained significant attention, and the proposed treatment of ectoparasite infections in aquaculture has the advantages of requiring reduced labor, and being cheaper and more sustainable (Powell et al., 2018). For instance, lumpfish Cylopterus lumpus were used to control sea lice Lepeophtheirus salmonis infestations attributed to this fish can graze on attached ectoparasite in Atlantic salmon (Imsland et al., 2014(Imsland et al., , 2016(Imsland et al., , 2019, and polyculture with shrimp protected farmed grouper from C. irritans infection and reduced C. irritans tomonts (Vaughan et al., 2018). ...
Marine cultured fish in tropical and sub-tropical regions often suffer from white spot disease, caused by Cryptocaryon irritans infection. This can lead to mass mortality and economic loss. This study investigated the use of seawater-adapted red tilapias (Oreochromis niloticus × O. mossambicus) as scavengers for cleaning tomonts, to protect susceptible marine fish from C. irritans infection. The sensitivity of red tilapia to C. irritans infection, the effectiveness of red tilapia in consuming tomonts, and the efficacy for protecting the vulnerable Trachinotus ovatus from C. irritans infection were evaluated. The results showed that the susceptibility of red tilapia to C. irritans infection was significantly lower than T. ovatus and the rate of tomonts consumption by red tilapia was positively correlated with the number of tomonts in the seawater. The relative percent survival of T. ovatus infected with C. irritans and co-cultured with red tilapias (at a density of 19 red tilapias/m²) was 97.78% at the12 days post-infection. This study indicates that polyculture with red tilapia could be a potential alternative biocontrol strategy to eliminate tomonts, for controlling C. irritans reinfection.
... This can involve the crafting of forms of non-human nature that correspond to new use values outside of a given commodity's conventional market. For example, lumpfish -once harvested as a source of caviar -is now farmed on an industrial scale as an 'organic' means to treat farmed salmon for sea lice instead of the use of pesticides (Imsland et al., 2018(Imsland et al., , 2019. As a strategy, commoditytransformation aims not simply to extend the geographies over which a given commodity is produced, or to enhance productive intensity at a given commodity frontier. ...
Research in political ecology and agrarian political economy has shown how commodity frontiers are constituted through the appropriation and transformation of nature. This work identifies two broad processes of socio-metabolism associated with commodity frontiers: the spatial extension of nature appropriation, via expanding territorial claims to the control and use of natural resources and associated acts of dispossession (commodity-widening); and the intensification of appropriation at existing sites, through socio-technical innovation and the growing capitalisation of production (commodity-deepening). While sympathetic, we have reservations about reducing frontier metabolism to either one or the other of these processes. We argue for more grounded examinations of how non-human nature is actively reconstituted at commodity frontiers, attuned to the diverse and specific ways in which socio-ecological processes are harnessed to dynamics of accumulation. To achieve this, we compare strategies of appropriation in three sectors often associated with the commodity frontier: gold mining, tree plantations and intensive aquaculture. In doing so, we bring research on capitalism as an ecological regime into conversation with work on the industrial dynamics of ‘nature-facing’ sectors. By harnessing the analytical categories of time, space and form adopted by research on industrial dynamics, we (i) show how strategies of commodity-widening and commodity-deepening are shaped in significant ways by the biophysical characteristics of these sectors; and (ii) identify a third strategy, beyond commodity-widening and commodity-deepening, that involves the active reconstitution of socio-ecological systems – we term this ‘commodity-transformation’.
... Clearly, reducing the risk of emaciation is a major challenge for the ethical use of lumpfish. This could be achieved by supplementary feeding, better diets, and novel feeding methods (Imsland et al., 2019a;Imsland et al., 2019d), but also by reducing stress and excessive energy expenditure. In this sense, our length-weight charts could be used by fish farmers to regularly monitor growth, and to take remedial actions before emaciation becomes a problem. ...
Lumpfish (Cyclopterus lumpus L.) are widely used for controlling sea lice in salmon farming, but their welfare is often challenged by poor husbandry, stress, and disease outbreaks, which compromise their ability to delouse salmon and cause public concern. It is hence important to identify when the welfare of lumpfish is being compromised in a simple and effective manner so that remedial actions can be taken. We developed, validated and tested a Lumpfish Operational Welfare Score Index (LOWSI) based on a visual assessment of skin and fin damage, eye condition, sucker deformities and relative weight, operational welfare indicators that fish farmers considered to be the most informative and were validated against cortisol measurements. We also present percentile length-weight charts to enable fish farmers to detect underweight and emaciated lumpfish at different stages of development. The lumpish welfare score index was quick and easy to score and was highly repeatable (intra class correlation coefficient = 0.83 ± 0.05). Most lumpfish (71%) displayed good welfare, but significant differences were found between six commercial sites and 28% of lumpfish had lower than normal weights for their length, and 10% were emaciated. The most common welfare problems were sucker deformities and fin damage in hatcheries, and poor eye condition and body damage in sea cages, conditions that may increase the risk of emaciation. Being able to score the welfare of lumpfish quickly and accurately will help improve their welfare, reduce stress-related mortalities, and improve the sustainability of the salmon farming industry.
... Lumpfish have in studies shown to lower sea lice infestation levels on affected salmon (Imsland et al., 2014a;Imsland et al., 2018a), but the species feeding behaviour is strongly opportunistic, and as such can vary with whatever food items are presentable (Imsland et al., 2014c;Eliasen et al., 2018). Sea lice foraging behaviour might be possible to improve using different implementations strategies (Imsland et al., 2016a;Imsland et al., 2016b;Imsland et al., 2019a). Recently, the current knowledge base of lice removal by cleaner fish has come under scrutiny for being far too limited and not reflecting the conditions within sea cages on commercially scaled levels (Overton et al., 2020). ...
Combating and controlling sea lice causes large economic costs for the farmers, with estimated values of more than 305 million euros (€) per year. Increased resistance against traditional chemotherapeutants due to evolutionary drivers in the sea lice combined with the lack of an effective vaccine and few other chemical treatments available are expected to cause these costs to increase. Several possible methods for managing sea lice infestations have been investigated, but only cleaner fish has proven to have an effect on lice levels. Cleaning activity is well known in marine fish and has been observed in the wild as a form of symbiosis between two species: one species, the ‘client’ fish, seek out the other species, the ‘cleaner’ fish, to have ectoparasites and dead tissue cleared from its body. The Atlantic lumpfish is a relatively new aquaculture species, and wild‐caught mature fish are used as brood stock for farmed production. This poses a biosecurity risk, as wild fish can carry pathogens, and the use of quarantine and health screening is recommended. Vaccine development is unfortunately lagging far behind relatively to the wide spread and high utilisation of the fish. This review contains description of the main pathogens and diseases that affect cleaner fish.
... The condition factor of lumpfish is higher than most other teleost, but the species follow an isometric growth pattern so the method of using condition factor is valid (Coull et al., 1989), and has been used as an indicator in several papers describing lumpfish growth (ex. Imsland et al., 2014aImsland et al., , 2018aImsland et al., , 2018bImsland et al., , 2019b. Specific growth rate (SGR) was calculated according to the formula of Houde and Schekter (1981) SGR = (e g − 1) × 100, where g = ln (W 2 ) − ln (W 1 ) / (t 2 − t 1 ) and W 2 and W 1 are weights on days t 2 and t 1 , respectively. ...
Cleaner fish used as a biological control agent against salmon lice is rapidly increasing in Atlantic salmon aquaculture. However, concerns have been raised about the welfare and mortality of cleaner fish in salmon cage systems, which could in turn affect their performance in controlling salmon lice. In a 4-month autumn-winter study, we monitored growth, welfare, mortality and daytime depth distribution of the most commonly used cleaner fish, farmed ballan wrasse and lumpfish, in six salmon production sea cages where thermo- and haloclines were present. Ballan wrasse did not grow (SGR: small: −0.01% day−1, large: −0.06% day−1), while lumpfish significantly doubled in size (SGR: 0.87% day−1) during the study. High losses (registered mortality + unregistered loss) were observed in both species (57 and 27% of ballan wrasse and lumpfish, respectively). The welfare status of remaining individuals generally improved over the study period, regardless of species. Brief daytime camera observations at hides found ballan wrasse were typically deeper at warmer (median 12.4 °C) more saline (median 31.7 ppt) depths, where salmon were expected to reside during day periods, compared to lumpfish generally occupying colder (median 7.3 °C), brackish (median 18.9 ppt) water in surface layers. Considerable mortalities, minimal feeding (inferred from ceased growth) by ballan wrasse and a possible mismatch in lumpfish and salmon depths (inferred from limited daytime camera observations) suggest that cleaner fish may have low long-term effectiveness against salmon lice in stratified salmon sea cages over autumn-winter. Similar studies across seasons, locations and cage types (e.g. depth-based cage technologies) are vital to understand the extent of these issues in salmon aquaculture more broadly.,
... All trials involving cleaner fish showed that they were effective in removing salmon lice from salmon, and that there was no evidence of a decrease in efficacy over time. On the contrary, there is a suggestion that treatments involving cleaner fish could be made more effective by selective breeding for cleaning behaviour and feeding on lice [42,50]. Cleaning behaviour performed by lumpfish or wrasse held together with Atlantic salmon can be considered as mutualism, because both species benefit from the interaction [51]. ...
The salmon louse (Lepeophtheirus salmonis) causes problems in Atlantic salmon (Salmo salar) aquaculture in the Northern Hemisphere, because infestations can result in both a loss of production and in fish mortality. Several types of treatment have been used to control louse infestations, but these have seen varying success. The aim of this review is to examine the efficacy and safety of commonly used treatments (chemical, biological, mechanical, and preventive measures) as documented in peer-reviewed publications. Efficacy is assessed in relation to a reduction in numbers of lice, and safety is assessed as a lack of negative treatment-associated effects on fish health and welfare (Atlantic salmon and/or cleaner fish). Most chemical treatments showed decreasing efficacy over time, together with the use of increasing concentrations as a result of the development of resistance to the treatments by lice. The need for a restrictive use of pesticides to preserve treatment efficacy has been emphasized. The use of cleaner fish was suggested to be effective, with few or no negative effects towards Atlantic salmon. The use of cleaner fish would be preferable to chemical treatment if the farmed fish health and welfare criteria are met. At present, the number of peer-reviewed publications relating to other forms of treatment and prevention are sparse.
... Accelerating this process by acclimating fish prior to stocking may therefore prove useful. Preliminary evidence at a small cage scale suggests that lice cleaning behaviour can be learnt more rapidly if cleaner fish are exposed to lice-infested sal mon or fed live feeds before stocking (Gentry 2018, Imsland et al. 2019); this should be tested further at a commercial scale before implementation. ...
Stocking cleaner fish to control sea lice infestations in Atlantic salmon farms is widespread and viewed as a salmon welfare-friendly alternative to current delousing control treatments. The escalating demand for cleaner fish (~60 million stocked per year) coupled with evidence of poor welfare and high mortality in sea cages requires that the lice removal effect of cleaner fish be substantiated by robust evidence. Here, we systematically analysed (1) studies that tested the delousing efficacy of cleaner fish species in tanks or sea cages, and (2) studies of spatial overlap, and therefore likely encounter rate, between cleaner fish and salmon when stocked together in sea cages. Only 11 studies compared lice removal between tanks or cages with and without cleaner fish using a replicated experimental design. Most studies had insufficient replication (1 or 2 replicates) and were conducted in small-scale tanks or cages which do not reflect the large volume, deep cages in which they are deployed commercially. Reported efficacies varied across species and experimental scale, from a 28% increase to a 100% reduction in lice numbers when cleaner fish were used. Further, our review revealed that the interaction of cleaner fish and salmon in sea cages has rarely been documented. While much of the evidence is promising, there is a mismatch between the current evidence and the extent of use by the industry. We recommend replicated studies in nine key areas at full commercial scale across all species that are currently widely used. More targeted, evidence-based use of cleaner fish should increase their efficacy and help to alleviate economic, environmental, and ethical concerns.
... In the present trial starvation was used to prime feeding in lumpfish. Alternatively, sea lice ice-cubes could be placed daily in the tanks up to one week before the actual collection of sea lice-eating lumpfish as recent research has indicated that sea lice eating can be enhanced by feeding juvenile lumpfish live Artemia nauplii together with frozen sea lice (Frogg, 2018). Smaller-sized lumpfish (< 50 g) should also be used for the experiment since they are known to have a stronger preference towards lice grazing than larger individuals (Imsland et al., 2016a). ...
In the present study, it was attempted to quantify sea lice grazing in lumpfish by using a recently published qPCR assay. This method utilizes a small aliquot (10 μL) of the stomach fluid of the lumpfish which can be collected using a sterile, 85 mm long pipette tip. We tested if repetitive sampling of stomach fluid influenced growth and survival in the sampled fish. The test lumpfish were sampled for stomach fluid at 6–16 days intervals for 95 days. No mortalities were recorded during the test period and there were no significant differences in growth compared to the control group. Quantification using the qPCR method was tested by two approaches; one with lumpfish that had grazed on sea lice ad libitum and the other with lumpfish that had been intubated with sea lice. The sea lice-specific qPCR assay had an inversely related relationship with the number of eaten lice, especially from stomach samples of lumpfish that naturally fed on sea lice as opposed to intubated fish.
Research in animal geographies is increasingly paying attention to hierarchies and inequalities within and between nonhuman animals. The way that animals are valued differently and hierarchically within this growing body of scholarship has tended to focus on a range of biopolitical differences between and within species. Collard and Dempsey’s recent contribution, in contrast, points to the importance of hierarchy and difference in the valuation of nonhuman animals under capitalism. Their framework identifies five orientations of human and nonhuman bodies in relation to capitalist value, which in turn provides a heuristic to explore how capitalist accumulation produces and depends on differentially oriented natures. Our contribution to these debates – and to the Collard and Dempsey framework – draws on our ongoing research in Eastern Canada where salmon aquaculture is a growing yet highly contested industry. We focus on two instances of multispecies hierarchy and difference in and around the salmon cage that are central to this form of ocean-based production. In focusing on multispecies relations, we build on Collard and Dempsey's framework in two main ways. First, we show how valuation and devaluation reflect competing but relational capitalist interests, which rely on and produce different natures refracted through the logic of the nature/culture divide: Atlantic salmon are valued as game fish, and as the key species for Canada's aquaculture sector. Second, we show how capital's valuation of one species, in our case farmed salmon, implicates the valuation of others, namely sea lice and lumpfish. Our case studies extend Collard and Dempsey's framework by demonstrating how capitalist differentiation produces violence through and outside of commodification in terms of multispecies difference and hierarchy; the lives and futures of wild and farmed salmon, lumpfish and sea lice are entangled, and reflect relational and changing orientations to capitalist value over time.
Lumpfish (Cyclopterus lumpus) are increasingly being used as cleaner fish to control parasitic sea-lice in salmon farming, but cleaning rates are very variable and not all individuals eat sea-lice, which increases the risk of emaciation and has ethical and practical implications. Selecting good cleaners is a priority to make the industry more sustainable, but there is little information on what behaviours make cleaner fish effective under a commercial setting. We examined variation in lumpfish personalities according to the five-factor personality model that takes into account differences in activity, anxiety (shelter use, thigmotaxis), aggression, sociality, and boldness (neophobia). We then quantified how variation in lumpfish personalities influenced interactions with naïve Atlantic salmon (Salmo salar), without the confounding effects of variation in sea-lice loads. Variation in activity, sociality, aggression and neophobia, but not in anxiety, was repeatable. Neophilic, non-aggressive lumpfish spent more time inspecting salmon than neophobic and aggressive individuals, but salmon fled in the presence of the most active and social individuals, suggesting there may be an optimal cleaner fish personality amenable to artificial selection. The personality screening protocols developed in this study could inform a more efficient use of cleaner fish in salmon farming and reduce the number of individuals required to control sea-lice.
Lumpfish (Cyclopterus lumpus L.) are increasingly being used as cleaner fish to control parasitic sea lice, one of the most important threats to salmon farming. However, lumpfish cannot survive feeding solely on sea lice, and their mortality in salmon net-pens can be high, which has welfare, ethical and economic implications. The industry is under increasing pressure to improve the welfare of lumpfish, but little guidance exists on how this can be achieved. We undertook a knowledge gap and prioritisation exercise using a Delphi approach with participants from the fish farming sector, animal welfare, academia and regulators to assess consensus on the main challenges and potential solutions for improving lumpfish welfare. Consensus among participants on the utility of 5 behavioural and 12 physical welfare indicators was high (87–89%), reliable (Cronbach's alpha = 0.79, 95CI = 0.69–0.92) and independent of participant background. Participants highlighted fin erosion and body damage as the most useful and practical operational welfare indicators, and blood parameters and behavioural indicators as the least practical. Species profiling revealed profound differences between Atlantic salmon and lumpfish in relation to behaviour, habitat preferences, nutritional needs and response to stress, suggesting that applying a common set of welfare standards to both species cohabiting in salmon net-pens may not work well for lumpfish. Our study offers 16 practical solutions for improving the welfare of lumpfish and illustrates the merits of the Delphi approach for achieving consensus among stakeholders on welfare needs, targeting research where is most needed and generating workable solutions.
The salmon aquaculture industry has adopted the use of invertivorous 'cleaner fishes' (CF) for biological control of sea lice infestations on farmed salmon. At present, ~50 million CF are used annually in Norway alone, with variable success in experimental and industrial contexts. We used a national-scale database of lice counts, delousing treatments and CF stocking events on Norwegian salmon farms to test for evidence of CF efficacy at 488 sites that completed a grow-out cycle within 2016-2018. Our analysis revealed that sites using more CF over the duration of a grow-out cycle did not have fewer lice on average, likely because CF use is reactive and in proportion to the scale of the lice problem. Over time within sites, we found that (i) sites using more CF early in the grow-out cycle were able to wait slightly longer (conservatively, a 5.2 week delay with 5000 CF stocked week-1) before conducting the first delousing treatment, and (ii) CF stocking events were followed, on average, by a small reduction in lice population growth rates. However, both effects were small and highly variable, and lice population growth rates remained positive on average, even when large numbers of CF were used (tens of thousands per site). Moreover, effects of CF on lice density tended to be short-lived, likely reflecting mortality and escape of stocked CF. Overall, the data indicate that while some sites consistently get good results from CF, there is also widespread suboptimal use. A better understanding of factors affecting CF efficacy in commercial sea cages is required to inform legislation and drive more efficient and ethical use of CF by the salmon aquaculture industry.
To assess the efficacy of lumpfish grazing on attached sea lice on Atlantic salmon, six large-scale sea cages, (130 m circumference, 37,688 m3 volume) each stocked with approximately 200,000 salmon 0+ smolts, were stocked with a 4, 6 and 8% density (8000, 12,000 and 16,000, respectively) of lumpfish. The sea cages without lumpfish acted as controls. Sea lice infestation levels on the salmon were monitored weekly and bi-weekly from 6 October to 17 May the subsequent year. Mortality of the lumpfish rose with decreasing sea temperatures to around 0.8% week-1 and did not vary between the lumpfish groups. There were clear signs of lumpfish grazing on sea lice, with significantly lower average levels of chalimus, pre-adult and adult female Lepeophtheirus salmonis and Caligus elongatus sea lice per salmon. Lumpfish in the high density (8%) group reduced the mature female L. salmonis to levels equal to or lower than the counts recorded prior to the start of the study. Overall, the present results indicate that lumpfish are a suitable cold-water option for biological delousing of Atlantic salmon in large-scale production conditions.
OPEN ACCESS: http://onlinelibrary.wiley.com/doi/10.1111/raq.12194/full
Efficient sea-lice control remains one of the most important challenges for the salmon
farming industry. The use of wrasse (Labridae) as cleaner fish offers an alternative
to medicines for sea-lice control, but wrasse tend to become inactive in
winter. Lumpfish (Cyclopterus lumpus) continue to feed on sea-lice at low temperatures,
and commercial production has escalated from thousands of fish in 2010
to well over 30 million juveniles deployed in 2016. However, production still
relies on the capture of wild broodstock, which may not be sustainable. To meet
global industry needs, lumpfish production needs to increase to reach c. 50 million
fish annually and this can only come from aquaculture. We review current
production methods and the use of lumpfish in sea cages and identify some of the
main challenges and bottlenecks facing lumpfish intensification. Our gap analysis
indicates that the areas in most need of research include better control of maturation
for year-round production; formulation of appropriate diets; artificial selection
of elite lines with desirable traits; and development of vaccines for certified,
disease-free juvenile production. The welfare of farmed lumpfish also needs to be
better quantified, and more information is needed on optimal densities and tank
design. Finally, the risk of farmed lumpfish escaping from net pens needs to be
critically assessed, and we argue that it might be beneficial to recover cleaner fish
from salmon cages after the production cycle, perhaps using them as broodstock,
for export to the Asian food markets or for the production of animal feeds.
Statement of relevance:
We believe that our manuscript is relevant for the aquaculture industry as it examines the growth performance of salmon in a fish farm in detail at a scale, both in terms of number of fish and in terms of duration, that is higher than usual for such studies. In addition, the fish contracted a disease (PD) midway through the experiment, thus resulting in a detailed dataset containing information on how PD affects salmon growth, which can serve as a foundation to understanding disease effects better. Furthermore, the manuscript describes an integrated mathematical model that is able to predict fish behaviour, growth and energetics of salmon in response to commercial production conditions, including a dynamic model of the distribution of feed pellets in the production volume. To our knowledge, there exist no models aspiring to estimate such a broad spectre of the dynamics in commercial aquaculture production cages. We believe this model could serve as a future tool to predict the dynamics in commercial aquaculture net pens, and that it could represent a building block that can be utilised in a future development of knowledge-driven decision-support tools for the salmon industry.
We studied the feeding ecology of juvenile lumpsuckers, Cyclopterus lumpus, during their first year in natural floating seaweed clumps and experimental floating seaweed branches, in southwest Iceland. The juveniles appeared to ignore sessile, slow-moving, and small animals (e.g., ostracods, bivalves, gastropods, oligochaetes, polychaetes, turbellarians, rotifers, and nematodes), while taking most other prey organisms in approximate proportion to availability. Juvenile lumpsuckers in floating seaweed fed mainly on prey organisms found on the seaweed but also consumed organisms from the plankton. Ontogenetic changes in the diet were related to size of prey. Lumpsuckers began to feed while they still had some yolk, primarily on small prey, including crustacean larvae and halacarid mites. After they completely absorbed their yolk, juveniles first fed largely on harpacticoids, but amphipods, isopods, and smaller juvenile lumpsuckers formed an increasing proportion of their diet as they grew. Behavioral selection of prey, rather than an increasing ability to ingest larger items, is suggested to be the basis for ontogenetic changes in diet.
The present study investigates vertical distribution of fish size in three 12 m × 12 m wide and 14 m deep
sea cages stocked with Atlantic salmon of average weight from 3.5 to 3.7 kg, at commercial densities between 15.6 to 16.2 kgm−3, in Norway. For each cage, individual fish weight were estimated by three 0.6 m × 0.6 m measuring frames as fish swam through. The frames were positioned at 3, 6 and 9 m depth. Recordings were carried out over five days per cage in succession, and during relatively stable environmental conditions in late autumn 2010. In all cages, measured fish were 15−25% smaller at 3 m compared to the average weights at 6 and 9 m depth. Largest average weight difference between depths within one cage was 0.995 kg. The average weight at 6 and 9 m was higher at night-time compared to daytime. Fish at the lower end of the weight spectrum were predominantly registered at 3 m, while fish at the higher end of the spectrum were mostly registered at the greater depths. Fish of average size were well represented at all three depths. The fact that smaller fish swam shallower may be ascribed to natural behavioural traits and introduce an important consideration in representative sampling within commercial sea cages. In biomass estimations and sea lice counts size-dependent vertical stratification needs to be accounted for.
1. In many species, individuals will alter their foraging strategy in response to changes in prey density. However, previous work has shown that prey density has differing effects on the foraging mode decisions of ectotherms as compared with endotherms. This is likely due to differences in metabolic demand; however, the relationship between metabolism and foraging mode choice in ectotherms has not been thoroughly studied. 2. Juvenile lumpfish Cyclopterus lumpus forage using one of two modes: they can actively search for prey while swimming, or they can 'sit-and-wait' for prey while clinging to the substrate using a ventral adhesive disk. The presence of these easily distinguishable foraging modes makes juvenile lumpfish ideal for the study of foraging mode choice in ectotherms. 3. Behavioural observations conducted during laboratory experiments showed that juvenile lumpfish predominantly use the 'cling' foraging mode when prey is abundant, but resort to the more costly 'swim' mode to seek out food when prey is scarce. The metabolic cost of active foraging was also quantified for juvenile lumpfish using swim-tunnel respirometry, and a model was devised to predict the prey density at which lumpfish should switch between the swim and cling foraging modes to maximize energy intake. 4. The results of this model do not agree with previous observations of lumpfish behaviour, and thus it appears that juvenile lumpfish do not try to maximize their net energetic gain. Instead, our data suggest that juvenile lumpfish forage in a manner that reduces activity and conserves space in their limited aerobic scope. This behavioural flexibility is of great benefit to this species, as it allows young individuals to divert energy towards growth as opposed to activity. In a broader context, our results support previous speculation that ectotherms often forage in a manner that maintains a minimum prey encounter rate, but does not necessarily maximize net energy gain.
Diseases are an important challenge in aquaculture. However, most of what is known about the effect of diseases comes from laboratory experiments. Using a farm-level data set containing sea lice infestation counts for all Norwegian salmon farms over an 84-month period, we empirically investigate the biological and economic impacts of observed levels of infective lice. Sea lice, a common ectoparasitic copepod of salmonids, have been shown to reduce fish growth and appetite and cause substantial costs to salmon farmers worldwide. Our results suggest that the percent of total biomass growth lost per production cycle due to average infestations varies from 3.62 to 16.55%, despite control, and depends on farm location. Using a discrete harvesting model, we simulate the economic impact on farm profits over typical cycles. An average infestation over a typical central region spring-release cycle generates damages of US436m in damages to the Norwegian industry in 2011.
To assess possible size effects of foraging of lumpfish and co-existence with Atlantic salmon with particular interest to the sea lice grazing efficiency, eight sea cages (5 × 5 × 5 m) were stocked with 150 Atlantic salmon with a mean (± SD) weight of 538 ± 14 g. Six of the cages were stocked with 15 lumpfish each (10% density), with two cages for each of three different size groups of lumpfish. Three duplicate groups of lumpfish with an initial mean (± SD) weight of 22.6 ± 0.7 g (small), 77.4 ± 3.6 g (medium) and 113.5 ± 2.1 g (large) were used in the study. Two cages without lumpfish acted as controls. Sea lice infestation levels were recorded at two to four week intervals for 159 days. To determine the diet preferences of lumpfish in the cages gastric lavage was performed at the same time intervals. Behaviour and growth of the lumpfish was assessed throughout the study period and mean weight of the Atlantic salmon measured at the start and end of the study period. From day 35 and onwards growth was higher for the small lumpfish group compared to the two other lumpfish size classes. Lumpfish from the smallest size class had a higher consumption of naturally occurring food items, including sea lice, compared to the other two size classes. Growth stimulation in salmon co-habiting the two smallest lumpfish size groups was observed. Signs of sexual maturation were found in the medium (13%) and the large (20%) size groups. Based on present data small lumpfish (initial size approx. 20 g) have a higher overall preference for natural food items compared to larger conspecifics. Although the sea lice infestation rate was low in the study (< 0.5 lice salmon− 1) final lice burden was 40% lower in salmon groups stocked with small lumpfish compared to the control group without lumpfish.
This study assessed the use of different types of substrates for lumpfish in sea pens. Observations were recorded in the early morning before first light, and the number of lumpfish attached to each surface type was recorded. The substrate was removed and another design was deployed if no lumpfish were attached to a substrate for more than 2 weeks. Lumpfish preferred flat and smooth vertical surfaces of plastic, as very few preferred to attach to stones and car tyres offered. Some lumpfish were also observed attaching to the floating seaweed placed into the cages, a more natural substrate used in the wild. It is concluded that lumpfish will easily adhere to artificial, smooth, plastic surfaces instead of natural surfaces such as kelp. Irrespective of the type of substrate offered, it is critical to the welfare of the fish that they have access to some form of substrate due to the need to rest and attach overnight.
For interval estimation of a proportion, coverage probabilities tend to be too large for "exact" confidence intervals based on inverting the binomial test and too small for the interval based on inverting the Wald large-sample normal test (i.e., sample proportion ± z-score × estimated standard error). Wilson's suggestion of inverting the related score test with null rather than estimated standard error yields coverage probabilities close to nominal confidence levels, even for very small sample sizes. The 95% score interval has similar behavior as the adjusted Wald interval obtained after adding two "successes" and two "failures" to the sample. In elementary courses, with the score and adjusted Wald methods it is unnecessary to provide students with awkward sample size guidelines.
The behaviour of lumpfish, Cyclopterus lumpus L., in sea pens, with and without Atlantic salmon, Salmo salar L., present, was assessed by underwater camera technology. Behaviour was classified by recording the principal activity of individual fish for 30-s intervals. The majority of daylight time was spent actively foraging for food. Antagonistic behaviour between Atlantic salmon and lumpfish was not observed during the whole experimental period and no mortality was seen in either species. Cleaning behaviour, but at low frequency, was observed as lumpfish cleaned sea lice off Atlantic salmon. Significantly lower sea lice infection levels were seen on Atlantic salmon when reared together with lumpfish compared to the control group without lumpfish. Feeding behaviour can be classified as strongly opportunistic.
Coastal floating seaweed, originating from the intertidal, is colonized by various pelagic and subtidal benthic animals. At southwestern Iceland, common macrofaunal colonizers include the fish Cyclopterus lumpus L., the harpacticoid Parathalestris croni (Krøyer), the amphipods Calliopius laeviusculus (Krøyer), Gammarellus angulosus (Rathke), Dexamine thea Boeck and Ischyrocerus anguipes (Krøyer), and the isopod Idotea baltica Pallas. The colonization patterns of these species were studied by collecting samples from experimental and natural clumps of floating seaweed at approximately monthly intervals for ca. 18 months. The occurrence of colonizers was highly seasonal with maximum numbers between April and September. For most species, numbers were correlated with weight of clumps. The relationship of density (numbers/100 g algae) to weight of clump and distance from shore varied between species. The algal species composition of clumps appeared to influence some colonizers. Only juvenile C. lumpus were found, while all P. croni were sexually mature; juveniles predominated in other species. The different colonization patterns of the species can be explained partly by their biological traits. The clumps are vital for the breeding of P. croni and are used for feeding by C. lumpus fry. Other species possibly colonize floating algae accidentally, being programmed to seek attached vegetation. Floating clumps may, nevertheless, serve to disperse these species.
Emamectin benzoate (EMB; SLICE®) has been the drug of choice for the control of sea lice in salmon aquaculture within the past decade due to its ease of administration as well as efficacy on all parasitic stages of sea lice. This over-reliance has led to increased tolerance to the drug and a consequent decline in its use. ATP-binding cassette (ABC) transporters such as P-glycoprotein (P-gp) are known to be involved in drug resistance. The present study investigated 1) the interaction of EMB with P-gp, 2) the effect of increasing EMB concentrations on P-gp mRNA expression in male and female sea lice, Lepeophtheirus salmonis, from Atlantic salmon (Salmo salar) farms in the Bay of Fundy, NB, as well as 3) changes in the mRNA expression of the transporter in archived adult female L. salmonis. Analysis of bioassay results indicated a 4 to 26 fold higher EMB EC50 for samples collected in 2011 compared to a similar study carried out between 2002 and 2004 suggesting loss of EMB efficacy in the parasite. An assay for ATPase activity as well as a competitive inhibition test showed that EMB interacts with the transporter. Emamectin benzoate had a significant concentration-dependent effect on P-gp mRNA expression in the parasite. There was a temporal increase in levels of P-gp mRNA in sea lice samples collected from 2002 to 2011. Our results indicate that EMB is a substrate for P-gp and that the transporter could be involved in the loss of efficacy of the parasiticide in L. salmonis.
Studies of the biology of sea lice have been conducted from various perspectives for two decades. For Lepeophtheirus spp., most of the published literature has centred on the economically important Lepeophtheirus salmonis, while for Caligus spp., research has focused on a wider range of species. The most numerous species of Caligus in North Atlantic waters, however, is Caligus elongatus, which is also economically important to salmon fanning. Since the last review by Pike, A. W., and Wadsworth, S. L. (1999. Sea lice on salmonids: their biology and control. Advances in Parasitology, 44: 234-337.), research on sea lice has developed considerably, including the application of genetic methods. This new research has focused on life history biology, studying developmental stages under different environmental conditions (e.g. temperature and salinity), behaviour, distribution and the dispersal of free-living stages, monitoring practices, population structure, and modelling. The results of this research have informed risk analyses and allowed the refinement of management strategies to reduce sea lice infestations in wild and fanned populations of anadromous salmonids. Molecular techniques have been used to describe population structure and identify differences in genetic characterization of geographically separate populations and population markers. Research has been initiated to understand the parasite-host relationship at a molecular level and to develop a vaccine against sea lice. (c) 2006 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved.
Lepeophtheirus salmonis (Copepoda: Caligoida) is an economically important marine ectoparasite of wild and pen-reared salmonids. The morphology of its developmental stages is described and compared with that of other species of Lepeophtheirus and Caligus. The development of L. salmonis is very similar to that reported for other Lepeophtheirus species. The appendages generally attain the adult condition and the sexes become distinguishable later in development than in Caligus species. At all developmental stages except the nauplius, L. salmonis can be distinguished from the co-occurring Caligus clemensi.
In 1994, more than 30 yrs after their first successful rearing through metamorphosis, the number of juveniles of the Japanese flounder (Paralichthys olivaceus) released to the sea exceeded that of the red sea bream (Pagrus major), the pioneer species in marine fish stock enhancement in Japan. Many features of the Japanese flounder make it a promising species for marine stock enhancement, but many problems must still be solved before further advances are possible. Of particular importance are the effects of temperature on growth and development, developmental endocrinology, differences between reared and wild juveniles in physiology and behavior, and the relationship between physiology and ecology.
For a fixed number of classes and the number of trials increasing, the approach of the multinomial cumulative distribution function to a normal cumulative distribution function is familiar. In this paper we allow the number of classes to increase as the number of trials increases, and show that under certain circumstances the probabilities assigned to arbitrary regions by the multinomial distribution are all close to the probabilities assigned by the distribution of “rounded off” normal random variables. As the number of trials increases, the amount rounded off approaches zero. The result can be used to study the asymptotic distribution of functions of multinomial random variables.
Prey selection and growth efficiency of juvenile sockeye salmon Oncorhynchus nerka switched between live prey and pelleted diets were investigated. First feeding sockeye salmon fry were placed into one of three dietary treatments for 7 months prior to assessing potential differences with a growth and a behavioural assay. Dietary treatments were (1) adult Artemia franciscana for 1 month, followed by pelleted feed for an additional 6 months (Art− BD), (2) pelleted feed from first feeding for 7 months (BD) and (3) adult A. franciscana for 1 month, and a combination of pelleted feed and live adult A. franciscana for 6 months (Art+ BD). Equal numbers from each treatment group were then tagged, pooled into replicate ‘common garden’ tanks and fed novel live prey items (Daphnia sp. and mosquito Culex pipiens larvae) for an additional 3 weeks. No significant differences in the growth efficiency of sockeye salmon were found during the 3 week feeding trial on the novel prey items. Additional sockeye salmon from each dietary treatment were used in a behavioural assay to determine if the treatments had an impact on foraging efficiency (prey selection or time to capture prey). No significant differences in prey selection were found among treatment groups in time to capture pellets, A. franciscana or mosquito larvae. Also, no significant differences were found within treatment groups in time to capture different food sources. No substantive benefits in foraging efficiency of sockeye salmon associated with prior exposure to live prey were demonstrated. This suggests that altering existing hatchery practices for juvenile sockeye salmon by offering live food prior to release is unlikely to influence post-hatchery feeding behaviour or increase post-release survival.
Trials were conducted in experimental tanks and in commercial scale sea cages to evaluate the ability of wrasse to control sea lice infestations on farmed Atlantic salmon smolts. In a 3 h tank trial rockcook wrasse, Centrolabrus exoletus (L.), removed an average of 19 lice per fish h−1 from salmon smolts infested mainly by Caligus elongatus Nordmann (93%) and with lower numbers of Lepeophtheirus salmonis (Krøyer) (7%). Goldsinny wrasse, Ctenolabrus rupestris (L.), did not remove lice from salmon over this 3 h period. Chalimus stages I and II were removed at a lower rate than were older and larger life history stages.Both species of wrasse failed to prevent rapid increases in infestations of C. elongatus in commercial cages in 1992 and 1993 at initial wrasse to salmon ratios ranging from 1:37 to 1:146. However, SCUBA diving observations confirmed that both wrasse species did remove C. elongatus from salmon in these cages.In the 10 m deep cages, wrasse occurred mainly at depths greater than 6 m while salmon occurred primarily between 2 and 5 m. Goldsinny had a significantly shallower distribution than rockcook. Both species associated closely with the cage net and with objects in the cage and interactions with salmon appeared to be relatively uncommon.Rigorously controlled trials on commercial farms need to be carried out in order to define protocol for the use of wrasse under these conditions.
The growth rate (% wt/day), depending on fish size (g) and water temperature (°C), has been estimated from a series of full-scale feeding experiments with Atlantic salmon (Salmo salar L.) and rainbow trout (Salmo gairdneri Richardson). The experiments were conducted with fish sizes between start feeding and 5 kg at temperatures from 2 to 16°C in fresh-water tanks and sea cages. The results are presented in three tables which may be helpful for the calculation of daily feed rations.
Freshly-hatched Artemia nauplii from various geographical sources survived storage in a refrigerator (2-4°C) at densities of 2000 per ml and above. Except for Artemia from Chaplin Lake and Buenos Aires, naupliar viability was very high even after 48 h storage, and did not decrease significantly after a 24 h post-storage transfer to 25°C. Neither the naupliar dry weight nor biochemical composition changed significantly during refrigeration for most strains tested. Comparative culture-tests with stored and freshly-hatched nauplii as food for juvenile marine mysids Mysidopsis bahia M. and larval carp Cyprinus carpio L. revealed similar production performances.
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.
© 2002 Society of Chemical Industry
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- F H Hoff
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