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Members of the myxovirus resistance (Mx) protein family play an essential role in antiviral immunity. They are Dynamin-like GTPases, induced by interferons. In the current study, we have characterized two predicted MX genes (MX 1 and MX 2) from lumpfish (Cyclopterus lumpus L.), having 12 and 13 exons, respectively. Mx2 has two isoforms (Mx2-X1 and Mx2-X2) which differ in exon 1. The lumpfish Mx proteins contain an N-terminal Dynamin-like GTPase domain, the middle domain (MD) and GTPase effector domain (GED) characteristic for Mx proteins. Phylogenetic analyses grouped all the lumpfish Mx sequences in group 1, and synteny analyses showed that both genes were localized at chromosome 5 in proximity to the genes Tohc7, Atxn7 and Psmd6. In vitro stimulation experiment showed that both MX1 and MX2 -X2 were highly upregulated upon exposure to poly(I:C), but not bacteria, 24 h post exposure, indicating their role in antiviral immunity. • Lumpfish have two functional MX genes. MX 1 and MX 2. • Isoforms exhibit distinct exon patterns, suggesting functional specialization. • In vitro stimulation experiment highlights their crucial role in antiviral immunity. • Establishment of qPCR assays provide an important tool to study antiviral responses in lumpfish in future studies. [ABSTRACT FROM AUTHOR]

Renibacterium salmoninarum causes Bacterial Kidney Disease (BKD) in several fish species. Atlantic lumpfish, a cleaner fish, is susceptible to R. salmoninarum. To profile the transcriptome response of lumpfish to R. salmoninarum at early and chronic infection stages, fish were intraperitoneally injected with either a high dose of R. salmoninarum (1 × 109 cells dose−1) or PBS (control). Head kidney tissue samples were collected at 28- and 98-days post-infection (dpi) for RNA sequencing. Transcriptomic profiling identified 1971 and 139 differentially expressed genes (DEGs) in infected compared with control samples at 28 and 98 dpi, respectively. At 28 dpi, R. salmoninarum -induced genes (n = 434) mainly involved in innate and adaptive immune response-related pathways, whereas R. salmoninarum -suppressed genes (n = 1537) were largely connected to amino acid metabolism and cellular processes. Cell-mediated immunity-related genes showed dysregulation at 98 dpi. Several immune-signalling pathways were dysregulated in response to R. salmoninarum , including apoptosis, alternative complement, JAK-STAT signalling, and MHC-I dependent pathways. In summary, R. salmoninarum causes immune suppression at early infection, whereas lumpfish induce a cell-mediated immune response at chronic infection. This study provides a complete depiction of diverse immune mechanisms dysregulated by R. salmoninarum in lumpfish and opens new avenues to develop immune prophylactic tools to prevent BKD. • Lumpfish head kidney transcriptome response to R. salmoninarum infection was reported. • R. salmoninarum causes immune suppression during early infection. • Lumpfish triggered cell-mediated immunity during chronic R. salmoninarum infection. • R. salmoninarum differentially regulated genes involved in lumpfish's apoptosis, alternative complement, JAK-STAT, and MHC-I pathways. [ABSTRACT FROM AUTHOR]

• The use of cleaner fish was not correlated with sea louse infestation density. • Farms that used many cleaner fish were able to wait longer before delousing. • Stocking cleaner fish slowed sea louse population growth over the next 12 weeks. • Effects were highly variable, resulting in weak effects when viewed at a national scale. The salmon aquaculture industry has adopted the use of invertivorous 'cleaner fishes' (CF) for biological control of sea louse 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 louse 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 louse 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 louse population growth rates. However, both effects were small and highly variable, and louse 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 louse density tended to be short-lived, likely reflecting mortality and escape of stocked CF. Overall, the data indicate that while some sites consistently obtain 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. [ABSTRACT FROM AUTHOR]

The objective of this study was to examine the effects of CO 2 , total ammonia nitrogen (TAN: nitrogen bound as either NH 3 or NH 4 +) and pH on the growth and survival of juvenile lumpfish in a two-month growth study. The results demonstrate the complex interactions of these water quality variables. The specific growth rate (SGR) of the lumpfish was progressively reduced with increasing [CO 2 ] concentration above 5–10 mg·L−1. However, growth may be reduced at even lower [CO 2 ] and the results provide no clear safe limits under which the growth of lumpfish is unaffected by CO 2 concentration. At the lowest [CO 2 ] tested (8 mg·L−1) the SGR was reduced compared with controls. Moreover, in treatments where the [CO 2 ] concentration increased to 8 mg·L−1 as pH was artificially reduced, the SGR was similarly reduced. These results indicate that lumpfish juveniles are very sensitive to increased [CO 2 ] concentration in water. The SGR of the lumpfish was progressively reduced as the NH 4 + concentration increased while maintaining the [NH 3 ] constant (70–80 μg·l−1). However, in these treatments the [CO 2 ] also increased to 8–10 mg·L−1 due to changes in pH and this likely contributed to reduced growth. Moreover, due to nitrification in the rearing systems, the nitrite concentration also increased to critical levels (1.5–4.2 mg·L−1) that could affect growth. Therefore, the results do not provide clear evidence for effects of increased NH 4 + on the growth of lumpfish. Taken together, the results of the experiments show that lumpfish are sensitive to perturbations in water quality and provide a benchmark for operational welfare indicators in lumpfish aquaculture. • The effects of CO 2 , total ammonia nitrogen (TAN) and pH on the growth and survival of lumpfish was studied. • pH in the range 7.2–7.8 does not directly affect the growth of lumpfish. • Growth is reduced at CO 2 concentration from 8 mg·l−1. • NH 3 at relatively low concentrations (0.08 mg·l−1) has negative effect on lumpfish growth. • Lumpfish are sensitive to perturbations in water quality. [ABSTRACT FROM AUTHOR]

Abstract Three duplicate groups of individually tagged lumpfish (mean initial weight: 22.3 ± 2.5 g) were fed either daily (7DW); four days per week (4DW) or three days per week (3DW) at a feeding rate of 2% body weight day−1 for a period of 126 days. There were significant differences in growth rates between the groups with the 7DW fish having the highest growth rates. Cataract prevalence was 53% lower in the 3DW group compared to the 7DW group. Histological examination showed that in some individuals in all three groups there was moderate expansion of the lamina propria in the mid and hind gut regions of the intestine with tissue most likely to represent fibrous tissue with scattered leucocytes. The severity of inflammation appeared to increase the more frequent the fish were fed with the 7DW fish having the highest inflammation score in these tissues. Feeding fish daily also resulted in higher levels of liver vacuolisation and chronic inflammation of the lamina propria in the mid and hind gut region of the intestines. Results from the present study show that restricted feeding regimes can be used to control growth and improve gut and eye health in lumpfish. Highlights • We assessed growth, cataract development and gut histopathology in lumpfish feed 7, 4 and 3 days per week (DW). • Growth and cataract prevalence was lowest in the 3DW group. • Liver vacuolisation and chronic inflammation in the gut was higher in the 7DW group. [ABSTRACT FROM AUTHOR]

Abstract 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. Highlights • It was attempted to quantify sea lice grazing in lumpfish by using a recently published PCR method. • The test lumpfish were sampled for stomach fluid at 6–16 days intervals for 95 days. • Stomach fluid sampling is safe for lumpfish, even when carried out regularly. • The sea lice-specific PCR assay had an inversely related relationship with the number of eaten lice. [ABSTRACT FROM AUTHOR]

Abstract In order to provide year round spawning broodstock, lumpfish (initial size 746 g and 24.9 cm) were reared under four different photoperiod regimes from January 2017 to July 2018. One group was reared under simulated natural photoperiod (LDN, control group) for Tromsø (70°N). The second group was transferred to continuous light (LD240) on 30 January 2017 and reared at LD24:0 throughout the trial period. Two compressed and phase advanced photoperiods were also established. Both groups were moved from LDN to LD24:0 on 30 January 2017, and after that reared at compressed natural photoperiods where the annual photoperiod was compressed down to six months (L6) or nine months (L9) for the duration of the study. Spawning time was shifted in both compressed groups during both years of the study. Spawning activity in the second year of the study was higher and followed more closely the expected spawning period in the compressed and the LDN groups. Spawning in the LD240 group was spread out over the experimental period with no distinct peak in spawning. A seasonal and pronounced drop in condition factor was found for females in the L9, L6 and the LDN groups. This post-spawning loss in condition was closely related to the spawning activity of each group. The current findings suggest that photoperiod has a strong influence on the timing of lumpfish maturation and can be used as an efficient and inexpensive tool to secure lumpfish reproduction operations i.e. year-round supply of egg and milt and/or timing with optimal temperature regimes. Highlights • We assessed the effects of different photoperiods to synchronize the spawning in cultured lumpfish broodstock. • First maturation in males was not dependent on photoperiod. • Spawning time was shifted in photoperiod manipulated groups during both years of the study. • Photoperiod can be used as an efficient and inexpensive tool to secure lumpfish reproduction operations. [ABSTRACT FROM AUTHOR]

Abstract Two batches of lumpfish eggs were incubated at three temperature regimes; 1-Ambient seawater 4–6 °C (cold), 2-Ambient seawater for 10 days followed by a gradual increase to 10 °C (gradient), 3-Constant 10 °C seawater (warm). The eggs incubated in cold water had the highest egg mortality (38.5% ± 15.7) and lowest hatching success (46.1% ± 7.2), while the gradient group regime showed highest hatching success (74.9% ± 4.2). Larvae from the gradient regime showed the most synchronized hatching as hatching started at 280 dd (35 days post fertilization (DPF)) and reached the hatching peak the same day with almost 80% of all larvae hatching. Hatching started at 279 dd (28 DPF) in the warm regime, reached a hatching peak (50% of total hatching) at 3 days post hatch (DPH), and ended at 9 DPH. In the cold temperature group hatcing started at 285 dd (63 DPF) and the hatching peak was reached at 3 DPH. Hatching lasted until 13 DPH. Hatched larvae from the cold regime were longest (6.11 mm) and heaviest (5.55 mg), followed by larvae from the gradient (5.71 mm, 4.88 mg) and warm (5.33 mm, 4.37 mg) regimes respectively. Newly hatched larvae from the warm group had the highest occurrence (34.7%) of body deformities compared to 8.9 and 7.6% in the gradient and cold water groups. Studies of organ and tissue histomorphology of hatched and two weeks old larvae did not reveal obvious developmental differences between the groups at these timepoints. Highlights • Lumpfish eggs were incubated at: a) ambient (4–6 °C), b) gradient (4 → 10 °C) or c) warm (10 °C) seawater. • The gradient group regime had the highest hatching success. • The larval mortality was highest in the warm group and lowest in the gradient group. • Newly hatched larvae from the warm group had the highest occurrence of body deformities. • A gradual rise in incubation temperature at the embryo stage may be beneficial for larval quality in lumpfish. [ABSTRACT FROM AUTHOR]

Abstract Decommissioning of offshore infrastructure has become a major issue facing the global offshore energy industry. In the North Sea alone, the decommissioning liability is estimated at £40 billion by 2040. Current international policy requires removal of offshore infrastructure when their production life ends; however, this policy is being questioned as emerging data reveal the importance of these structures to fish and invertebrate populations. Indeed, some governments are developing 'rigs-to-reef' (RTR) policies in situations where offshore infrastructure is demonstrated to have important environmental benefits. Using Remotely Operated Vehicles (ROVs), this study quantified and analysed fish and invertebrate assemblage dynamics associated with an oil and gas (O&G) complex in the Dogger Bank Special Area of Conservation (SAC), in the North Sea, Germany. We found clear depth zonation of organisms: infralittoral communities (0–15 m), circalittoral assemblages (15–45 m) and epi-benthic communities (45–50 m), which implies that 'topping' or 'toppling' decommissioning strategies could eliminate communities that are unique to the upper zones. Sessile invertebrate assemblages were significantly different between structures, which appeared to be driven by both biotic and abiotic mechanisms. The O&G complex accommodated diverse and abundant motile invertebrate and fish assemblages within which the whelk Buccinium undatum , cod fish Gadus morhua and lumpsucker fish Cyclopterus lumpus used the infrastructure for different stages of reproduction. This observation of breeding implies that the structures may be producing more fish and invertebrates, as opposed to simply acting as sites of attraction (sensu the 'attraction vs production' debate). At present, there are no records of C. lumpus spawning at such depth and distance from the coast, and this is the first published evidence of this species using an offshore structure as a spawning site. Overall, this study provides important new insight into the role of offshore O&G structures as habitat for fish and invertebrates in the North Sea, thereby helping to inform decommissioning decisions. Highlights • Decommissioning of North Sea oil and gas infrastructure is a £40 billion liability. • We assessed fish and invertebrate habitat value of a North Sea oil and gas complex. • A diverse range of reef-dependent and transient pelagic species were observed. • Clear depth zonation occurred, helping inform in situ decommissioning strategies. • Evidence of reproduction suggests the complex was producing fish-invertebrates. [ABSTRACT FROM AUTHOR]

A passive-acoustic telemetry system was used for the first time for the fine-scale, three-dimensional tracking of individual cleaner fish in commercial Scottish salmon sea-pens in full commercial operation. The aim was to test the system performance and provide baseline data on the comparative distribution and swimming activity of individual ballan wrasse and lumpfish under standard farm practices with the long-term aim of informing stocking and husbandry strategies. In March 2015, wild ballan wrasse ( Labrus bergylta ) (115 ± 20 g; n  = 13) and farmed lumpfish ( Cyclopterus lumpus ) (281 ± 42 g; n = 13) previously deployed in June–October 2014 were recaptured, implanted with acoustic tags pinging every 6–12 s and released into their original sea cage holding Atlantic salmon (Q2 2014; 2059 ± 35 g mean-weight). Control tags were deployed in cleaner fish hides to validate the system performance. Positional data from nine specimens per species were analysed from March 24th to June 1st 2015, during which time water temperature rose from 7.2 to 9.1 °C and water salinity averaged 26.8 ± 1.5 ppt at 4 m depth. The accuracy of the acoustic positions averaged 0.6 m across the three dimensions of all control tags and was <1 m in 93% of all cases. Significant differences in the distribution and activity of ballan wrasse and lumpfish were observed. Ballan wrasses spent 60 ± 2% of the day-time at or below 15 m, were positioned at significantly shallower depths at night and seldom used the hides provided despite an apparent resting behaviour at the pen bottom and corners. In comparison, lumpfish spent over 80% of the time above 10 m, used hides extensively and preferentially at night (50.1 ± 2.1% at night), but to a lesser extent when the water temperature increased. The acoustic tracking system proved to be an effective tool for visualising cleaner fish behaviour under challenging farm conditions, and the study highlights the critical role of hides in cleaner fish husbandry. Overall, the study quantified species-specific cleaner fish distribution in salmon net-pens supporting distinct interactions with the salmon stock and seasonal behaviour profiles. The results support the current commercial strategy of using two cleaner fish species against sea lice and the need for species-specific management strategies to optimise delousing activity. [ABSTRACT FROM AUTHOR]

Sea lice infestations causes major economic losses in the Atlantic salmon aquaculture industry, and cleaner fish, e.g. the lumpfish, Cyclopterus lumpus L., are therefore increasingly deployed as a biological control method. However, large variations in the cleaning efficacy have been observed, and in the Faroe Islands, the most prominent variation is seasonal. Over a period of approximately two years 5511 lumpfish stomachs were analysed. The stomach contents, where present, were identified and grouped as, a) sea lice, b) lumpfish feed, c) salmon feed, d) organisms associated with biofouling, e) zooplankton organisms and/or f) other. The presence of zooplankton organisms had a significant, and negative, influence on the cleaning efficacy, while the presence of organisms associated with biofouling had a more moderate, but positive, influence on the prevalence of sea lice in the lumpfish diet. Our findings indicate that biofouling, and the subsequent availability of alternative prey organisms, does not reduce the cleaning efficacy of lumpfish, while zooplankton does, i.e. reducing it by a factor of approximately five. The lumpfish size only seemed to play a minor role in the variation observed in the cleaning efficacy, while it had a significant influence on the proportion of empty stomachs, i.e. the smaller lumpfish (< 50 g) had the highest occurrence of empty stomachs. This is convenient knowledge for implementation in the sea lice strategies of farming sites using lumpfish as cleaner fish in general, but especially in farming areas with large seasonal variations in the zooplankton abundance such as in the Faroes. The high occurrence of empty stomachs in small lumpfish highlights the necessity to adapt husbandry in the first period post lumpfish deployment, especially when the opportunity for naturally occurring food is sparse. Furthermore, our findings of biofouling having a positive influence on the grazing efficacy of lumpfish indicate that net cleaning might have a negative influence on lumpfish grazing efficacy. [ABSTRACT FROM AUTHOR]

From an aquaculture point of view, control of the sexual maturation cycle is critical for a sustainable production of the species. For year-round reliable production of juvenile lumpfish of the appropriate size for stocking salmon cages, there is a need for basic and applied knowledge on the control of sexual maturation in cultured lumpfish broodstock. Lumpfish (initial size 219 g and 16.9 cm) were reared under advanced simulated natural photoperiod (SLDN, control group) for Tromsø (70°N). In addition there were two groups exposed to continuous light from April 2014 to January 2015 (PP3) and from April 2014 to April 2015 (PP6) followed by 8 week decline in hours of light from 24 to 4 h (autumn signal) and subsequent 8 week rise from 4 to 24 h (spring signal). Exposure of lumpfish to continuous light followed by an autumn-spring signal stimulated somatic growth and affected age at first maturity in females. The growth enhancing effect of continuous light lasting for approximately six months in females compared to one month in the males. Spawning colouration and running milt was seen in males in all three photoperiod groups from September 2014 onwards indicating that maturation started prior to the experimental treatment. In the females spawning time, egg volume and hatching success varied between the photoperiod groups. No spawning occurred in the SLND group, whereas spawning was seen in both PP female groups 3–6 months after the onset of short autumn-short spring photoperiodic signal. Hatching success was higher in the PP3 group (83.4%) compared to the PP6 group (72.3%). The current findings are the first step in the development of photoperiod regimes which may provide simple and effective off-season maturation in lumpfish. [ABSTRACT FROM AUTHOR]

The female portion of the population of lumpfish ( Cyclopterus lumpus ) in Iceland is currently monitored using a biomass index calculated using catch data from the Icelandic spring groundfish survey (referred to as the spring survey). This has been controversial among lumpfish fishers who insist that the behaviour and variations in the migration of lumpfish make the use of this survey inappropriate for assessment. To evaluate whether changes in the biomass index from the spring survey adequately reflect changes in the population, the spatial and depth distribution of catches of lumpfish from this survey are compared with the total coverage of the survey. The biomass index from the spring survey is also considered alongside data from two other surveys (gillnet survey and autumn groundfish survey) and catch per unit effort (CPUE) from the female lumpfish fishery. In the spring survey, female lumpfish were predominantly caught at depths shallower than 300 m and within 100 km of shore, while the survey extends to a depth of 500 m and 227 km from shore, indicating that survey coverage was fitting for this species. The changes in the biomass index from the spring survey were similar to that of the gillnet survey, and also to changes in CPUE of the fishery. A decrease in the biomass index of large lumpfish (≥45 cm) caught during the survey was correlated with the decreasing use of large mesh sizes in the fishery indicating that changes in size distribution in the population could be detected using the spring survey. These results indicate that the use of the spring survey to monitor changes in lumpfish population in Iceland is justified. The use of data from bottom trawl surveys to track lumpfish populations in other regions is discussed. [ABSTRACT FROM AUTHOR]

Cleaner fish such as lumpfish ( Cyclopterus lumpus L.) and ballan wrasse ( Labrus bergylta A.) are increasingly used to delouse farmed Atlantic salmon ( Salmo salar L.). In 2014, > 20 million cleaner fish were placed into net-pens with farmed salmon in Norway. Amoebic gill disease (AGD), caused by the opportunistic, parasitic amoeba Paramoeba perurans , is emerging in salmon farming in Northern Europe. The amoeba displays low host specificity as it has been isolated from a range of fish species in addition to salmonids, such as wrasse and lumpfish cohabitating with farmed salmon. It is, however, not known to which degree lumpfish respond to P. perurans challenge, to which extent lumpfish may develop AGD, and if they can function as a vector for the spread of P. perurans to salmon. The present study shows that lumpfish can be infected with P. perurans under experimental conditions and develop AGD. However, lumpfish are more resistant and the development of pathology is slower compared to salmon. It is also shown that lumpfish can act as carriers and transmit parasitic amoebae to Atlantic salmon. Importantly, it is demonstrated that the gill lesion score system extensively used for evaluating AGD in Atlantic salmon is less suitable for lumpfish infected with P. perurans as the disease develops more slowly in lumpfish and because lumpfish may be non-symptomatic carriers. Statement of relevance 1) The last few years, lumpfish have been used as cleaner fish in order to delouse farmed Atlantic salmon. However, nothing is yet known about its susceptibility to the parasitic amoeba P. perurans. 2) Currently, nothing is known about amoebic gill disease (AGD) development in lumpfish and the possibility that amoeba may be transferred from lumpfish to salmon. 3) There is currently little information about the pathology (macroscopic and histological changes) in lumpfish. 4) We have found that the commonly used gill scoring system for salmon is not applicable for lumpfish, and we recommend that the lumpfish is screened, not scored before transfer to net-pens with salmon. [ABSTRACT FROM AUTHOR]

Lumpfish ( Cyclopterus lumpus ) is currently used as cleaner fish in Norwegian Atlantic salmon ( Salmo salar ) farming to control parasitic lice on salmon. The need for high numbers of lumpfish necessitates intensive farming of this species but very limited knowledge is available on the environmental requirements of lumpfish in culture. The present study was therefore carried out to investigate the tolerance of lumpfish to varying water exchange rates and oxygen saturations. Four triplicated treatment groups were established at different water exchange rates, which caused oxygen saturations of 55% (0.7 L min − 1 ), 69% (1.2 L min − 1 ), 81% (1.9 L min − 1 ) and 96% (6 L min − 1 ). Decreasing water exchange rate and oxygen saturations negatively affected growth, even in the fish groups held at 81% oxygen saturation. The fish group held at 55% oxygen saturation had almost no growth in body mass and showed sign of fin-infections and were terminated halfway through the experiment. A high workload associated with oxygen extraction and reduced appetite is considered the reason for reduced growth at lower oxygen saturations. While plasma cortisol levels in the groups held at 81 and 96% oxygen saturation corresponded to those considered typical for unstressed fish (< 10 ng mL − 1 ), the levels of plasma cortisol of fish in the 69 and 55% oxygen saturation groups were above 20 ng mL − 1 in November, indicating a state of chronic stress. A fast, albeit weak, cortisol response to stressors in the lumpfish was confirmed in a separate, 2 h long acute handling and hypoxia experiment. Lack of differences between treatments in plasma lactate levels indicates that the lumpfish reduced their food intake and locomotory activity sufficiently to avoid resorting to anaerobic metabolism when exposed to reduced oxygen saturations. It is concluded that the juvenile lumpfish is sensitive to reduced water oxygen saturations and that oxygen saturations below 80% in aquaculture should be avoided. [ABSTRACT FROM AUTHOR]

Lumpfish males usually release small amounts of milt and are therefore often sacrificed for surgical harvesting of gonads. To optimize the utilization of sperm obtained by dissection of the gonads, a series of small-scale fertilization experiments was carried out in petri dishes. Sperm extracted from homogenized gonads were diluted 1:1 with a commercial extender solution before use (AquaBoost®SpermCoat). Fertilization success was evaluated as percentage eyed eggs ∼120 day-degrees post fertilization. Firstly, the effect of chilled storage (3 °C) of diluted milt were evaluated by fertilizing eggs (2.27 × 105 sperm/egg) from two freshly stripped females every 2nd or 3rd day over a 14-day period. Storage time did not affect the fertilization rates which were high throughout the 14-days trial period (89.1–99.8%). Secondly, the effect of sperm to egg ratio of cryopreserved and chilled stored sperm (3 °C for 3 days) on fertilization rate was investigated and compared by fertilizing eggs from three separate females with six different sperm to egg ratios (1.25 × 105 to 2 × 109). For both storage methods, only the lowest sperm to egg ratio (1.25 × 105) resulted in a significant lower but still high fertilization rate (80.7%). Using freshly extracted sperm at lower sperm to egg ratios (1.25 × 105 to 3.1 × 104) to fertilize eggs from three females revealed, however, no relationship between sperm to egg ratio and fertilization rates as they were high for all ratios (91.2–93.4%). Two additional experiments were undertaken at a real scale to validate the petri dish results at higher egg numbers and volumes. A fixed volume of 40 ml eggs (∼4800 eggs) was fertilized with four sperm to egg ratios ranging from 3.1 × 104 to 5 × 105. All sperm to egg ratios resulted in high fertilization rates ranging from 93.7 to 99%. In the second real scale experiment increasing volumes of eggs (1 up to 160 ml) were fertilized with a fixed sperm to egg ratio (2.5 × 105). The fertilization success (95.9–97.5%) was not affected by egg volume. In conclusion, the current study showed that lumpfish sperm can be chilled stored at 3–4 °C for 14 days and can be cryopreserved and thawed without any significant reduction in fertilization success under the conditions used in this study. Compared to other marine teleosts, lumpfish require a low sperm to egg ratio for successful fertilization, but the critical low ratio to obtain high fertilization was not revealed in this study. • No reduction in fertilization after 14 days chilled storage of lumpfish milt. • Low sperm to egg ratios needed to achieve high fertilization rates in lumpfish. • Similar fertilization with cryopreserved and chilled stored lumpfish sperm. [ABSTRACT FROM AUTHOR]

Lumpfish are currently used as a part of the overall strategy for the prevention and control of sea lice in Atlantic salmon farming in Norway. Their use as biological delousers is advantageous as it exposes salmon to very little stress and injuries. However, there is a growing concern and criticism about the welfare and survival of lumpfish in salmon farms. This study monitored the welfare and survival of lumpfish from four commercial salmon farms for 6 to 12 months in 2019–2021. Environmental and production conditions were also registered. Lumpfish welfare decreased during the study period, mainly related to eye and skin injuries. Mortality rate was low in the first few months after transfer to sea, but increased thereafter. Mechanical delousing affected the welfare and survival most negatively of all monitored external parameters. Even though diseases are often pointed out as the main factor for mortality of lumpfish in sea cages, it was not the case in the present study. However, there were indications that diseases are more likely to occur when lumpfish is already weakened by other factors such as mechanical delousing. One to two thirds of lumpfish were assessed as underweighted or emaciated at all time during the monitoring period, suggesting that the nutritional requirements of lumpfish are not fully met in sea cages. • Lumpfish welfare decreased during the study period, mainly related to eye and skin injuries. • Mortality rate was low in the first few months after transfer to sea, but increased thereafter. • Lumpfish welfare and survival were most negatively affected by mechanical delousing. • Diseases may be more likely to occur when lumpfish is already weakened by other factors such as mechanical delousing. • The nutritional requirements of lumpfish may not be fully met in sea cages. [ABSTRACT FROM AUTHOR]

Lumpfish (Cyclopterus lumpus) aquaculture has expanded greatly in recent years due to demands for sea lice cleanerfish from the salmon industry. There are knowledge gaps in lumpfish digestive physiology, nutrient requirement and implications of nutrition for health and disease susceptibility. The present study, conducted to follow up our recent screening trials for estimation of optimal balance of protein, lipid and carbohydrate in diets for lumpfish, involved challenging the fish with Aeromonas salmonicida after a feeding period with diets varying in lipid composition. Three experimental diets were formulated to have similar content of digestible protein and carbohydrate but varying in content of lipid from 6.7 to 18%. Lumpfish with average body weight at start of 1.7 ± 0.03 g were fed the experimental diets in triplicate tanks each (110 fish per tank, in total 990 fish in 9 tanks) for a period of 90 days. After termination of the feeding trial and subsequent collection of biological samples, remaining fish were challenged with atypical A. salmonicida. No significant effects of diet were observed for growth performance. Carcass composition showed increasing content of lipid, protein, and energy with increasing dietary lipid level. Increasing dietary lipid also increased hepatic dry matter, lipid and energy levels, while crude protein decreased. Blood plasma nutrient levels and biomarkers of liver function showed few significant effects of diet, but dietary lipid level increased plasma cholesterol. Intestinal trypsin activity increased with increasing dietary lipid, whereas activity of other digestive enzymes and digesta bile salt levels were unaffected by diet. Increasing lipid level also increased lipid accumulation in the proximal and mid intestine. Expression profiling of genes related to digestive and immune function showed few effects of diet, but the nutrient transporters fabp2 and slc15a1 , as well as the immune genes MHCII, igm , and nfkb showed increases with dietary lipid levels, whereas the cholesterol transporter npc1l1 was suppressed. Diet composition did not affect the lumpfish' resistance against A. salmonicida. To conclude, the variation in macronutrient composition induced modulations in metabolic, digestive and some immune functions. Modulations seemed however to be within normal ranges and did not produce clear compromises in immune responses to bacterial infection. • Increasing dietary lipid level increased body and liver fat while growth performance was not affected. • High dietary lipid level resulted in intracellular lipid accumulation of enterocytes and elevated level of blood cholesterol. • Lipid composition did not impact immune responses even under the challenge of Aeromonas salmonicida. [ABSTRACT FROM AUTHOR]

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. Statement of relevance The data presented here are highly relevant for Aquaculture as the effective use of lumpfish for biological delousing of salmon is very important for commercial aquaculture of Atlantic salmon. [ABSTRACT FROM AUTHOR]

The use of cleaner fish as biological controls of salmon lice ( Lepeophtheirus salmonis ) has increased exponentially in the last decade in Norwegian Atlantic salmon ( Salmo salar ) production. This alternative to chemical treatments has resulted in the emergence of lumpsucker ( Cyclopterus lumpus ) hatcheries and culture facilities in Norway. It has been shown that the use of lumpsuckers can be an effective, biological approach for the removal of salmon lice, but it has also been shown that there are a number of biological challenges (i.e. parasites and bacteria) with the production and use of these fish. This study describes the first case of isolation of Tenacibaculum maritimum , a significant fish pathogen worldwide, in cultured juvenile lumpsuckers in Norway. The fish were lethargic and showed skin lesions characterised by increased mucus production and presence of whitish necrotic tissue especially in the head region. Skin scrapings revealed large amounts of bacteria dominated by rod-shaped Tenacibaculum -like bacteria, which were shown to be closely related to T. maritimum type strain through genetic and phenotypic characterisation. Histopathological analysis showed that the bacteria was closely associated with the pathology and therefore could be contributing to the disease and/or mortality. Statement of relevance This is the first isolation of Tenacibaculum maritimum in Norway and in lumpsuckers, a major aquaculture pathogen worldwide. There is a need for increased knowledge of the biological challenges facing cultured lumpsuckers, as this species is being used in increasing number by the Norwegian salmon industry. [ABSTRACT FROM AUTHOR]

To investigate the possible family influence on sea lice grazing of lumpfish on Atlantic salmon, nine families of lumpfish (N = 360) with a mean (± SD) weight of 169.4 ± 8.3 g were distributed among nine sea cages (5 × 5 × 5 m) each stocked with 400 Atlantic salmon with a mean (± SD) weight of 123.3 ± 12.3 g. For each family, 20 lumpfish were stocked into one of nine sea cages and 20 into another cage thus establishing duplicate treatments for each genetic family giving two families stocked per cage. There were significant differences in behaviour, feeding preferences and mortality between the nine families of lumpfish. Fish from family 2 were found to be more predisposed to exploiting natural food sources within the cage environment and showed a higher incidence of sea lice grazing from Atlantic salmon. Using mixed linear model to analyse the data revealed significant maternal and paternal effect on sea lice grazing. In contrast, fish from family 5 were observed choosing to compete with salmon and consume pellets more than the other eight families and were found to be less inclined in seeking out alternative food sources. Further, there were differences in the mortality rates between the nine families as a result of a Pasteurella spp. outbreak. This is probably the first study in fish aquaculture investigating the variation in a specific behavioral trait linked to different family background. Statement of relevance The data presented here are highly relevant for aquaculture. [ABSTRACT FROM AUTHOR]

Cleaner fish are commonly used as a control measure against salmon lice infestations in salmonid farms. Lumpfish (Cyclopterus lumpus) is the most common cleaner fish species used in Norwegian farms. However, little is known about how different operational, including environmental, conditions affect the salmon lice grazing efficacy by lumpfish. In this paper, we analyse salmon lice (Lepeophtheirus salmonis) in the stomach contents of a large sample of more than 20,000 lumpfish from 80 different Norwegian farms. We investigate the proportion of lumpfish with salmon lice and the mean number of salmon lice in the stomach contents of the lumpfish. We further explore how the salmon lice contents vary with different factors like lumpfish weight, weight of salmonids, salmon lice abundance in the cage, cloud cover, and sea temperature. We find that 3.1% of the 24,693 lumpfish contained salmon lice. Most of the lumpfish with salmon lice in their stomach contents contained few (one or two) lice, while there were a few lumpfish which contained many salmon lice. We find more salmon lice in the stomach contents with increasing abundance of salmon lice in the sea cage, lower weight of the salmonids, and in clear weather. Interestingly, for the relationship between lumpfish weight and salmon lice in the stomach contents, we find increased salmon lice grazing from ca. 5 g up to an optimal weight of ca. 40 g, and then a decrease from 40 g. Surprisingly, we find no relationship between sea temperature and salmon lice per lumpfish. We find more salmon lice in the stomach contents of the lumpfish with comparatively high condition. By studying the factors associated with most efficient salmon lice grazing, our paper contributes to understanding how different operational factors affect salmon lice grazing by lumpfish. For controllable factors, the results thus contribute to guiding the best practice for use of lumpfish as a salmon lice control measure. • 3.1% of the lumpfish stomach samples contained salmon lice. • We found more lice per lumpfish with increasing abundance of lice on the salmonids. • We found an optimal lumpfish weight for salmon lice grazing of ca. 40 g. • We found no relationship between sea temperature and salmon lice per lumpfish. • We found more lice per lumpfish for higher condition and in clear weather. [ABSTRACT FROM AUTHOR]

This study investigated the effects of plant protein concentrates on the activity of digestive enzymes and microscopic structure of the intestine of juvenile lumpfish. The experiment was carried out using triplicate groups of lumpfish of 7 g average initial body weight, to 40 g average final weight, after 54 days. Four experimental diets were used; a fishmeal (FM) based control diet and three test diets with the plant protein concentrates; soy protein concentrate (SPC) and pea protein concentrate (PPC) (1:1 ratio) replacing FM in proportions of 25% (PP25), 50% (PP50) and 75% (PP75), respectively. Nested ANOVA showed several significant treatment differences in histomorphometry. Overall, fish fed test diets exhibited several changes such as shorter mucosal fold height (MFH) in the anterior intestine (AI), increased number of goblet cells (GCs) and width of lamina propria (WLP) in distal intestine (DI), compared to control. Principal component analysis (PCA) on histological indices showed that all three treatment groups (i.e. PP25, PP50 and PP75) had significantly altered overall intestinal architecture, compared to the control group. The observed enteritis was negatively related with the condition factor (CF). Regarding enzyme activities fewer changes were observed across diets. Fish fed the PP50 diet exhibited an increased activity of leucine aminopeptidase (LAP) in the pyloric caeca and a decrease on chymotrypsin (CHY) in the mid intestine (MI) compared to the control. Nevertheless, the overall changes captured by PCA on enzymes were associated only with condition factor (CF) and not with the diets. Overall, histological evaluation confirmed that lumpfish intestinal morphometry was significantly altered by plant protein ingredients at 25%, 50% and 75% levels, but replacing of FM up to 50% did not affected the growth and the enzyme activities up to 75% inclusion level. • 25–75% fishmeal replacement affects intestinal histology not enzymatic activity • Intestinal histology was associated with CF • Intestinal enzymatic activity was significantly associated with CF, not the diet [ABSTRACT FROM AUTHOR]

The innate immune responses in lumpfish (C yclopterus lumpus L.) have been shown to be functional, but little is currently known about the B cells, immunoglobulins or adaptive immune responses in this species. We have used anti-IgM antiserum to isolate B cells and compared them morphologically and functionally with other cell types. The fraction of IgM + cells among isolated peripheral blood leukocytes (PBL), head kidney leukocytes (HKL) and spleen leukocytes (SL) was in the range of 40%, 12% and 34%, respectively. The IgM + B cells had high phagocytic ability and were the predominant phagocytes in blood with higher capacity than IgM + B cells in HKL. Interestingly, among PBL, the most potent phagocytes were, in addition to monocytes, some small agranular uncharacterized IgM − cells. The IgM + B cells were positive for acid phosphatases (AcP), but negative for myeloperoxidase (MPO). Neutrophils were positive for MPO, while monocytes/macrophages and dendritic-like cells stained negatively. Monocytes/macrophages and the small, agranular IgM − cells stained most strongly positive for AcP corresponding to their high phagocytic capacity. Further, the ability to produce specific antibodies upon immunization verified adaptive immunity in the species. The high proportion of phagocytic IgM + B cells and their phagocytic ability indicate a significant role of phagocytic B cells in lumpfish innate immunity. The present analyses also give strong indications that vaccination and immunostimulation of farmed lumpfish can be used to prevent disease and mortality caused by pathogenic organisms. [ABSTRACT FROM AUTHOR]

Concentration dependent differences in acute and long-term effects of a 48 h exposure to mechanically or chemically dispersed crude oil were assessed on juvenile lumpsucker ( Cyclopterus lumpus ). Acute or post-exposure mortality was only observed at oil concentrations representing higher concentrations than reported after real oil spills. Acute mortality was more apparent in chemically than mechanically dispersed oil treatments whereas comparable EC 50 s were observed for narcosis. There was a positive correlation between EROD activity and muscle PAH concentration for the lower oil concentrations whereas higher concentrations inhibited the enzyme activity. The incidence of gill tissue lesions was low with no difference between dispersion methods or oil concentrations. A concentration dependent decrease in swimming- and feeding behavior and in SGR was observed at the start of the post-exposure period, but with no differences between corresponding oil treatments. Three weeks post-exposure, fish from all treatments showed as high SGR as the control fish. [ABSTRACT FROM AUTHOR]

The genus Aeromonas is found worldwide in freshwater and marine environments and has been implicated in the etiology of human and animal diseases. In fish, among Aeromonas species, A. salmonicida causes massive mortality and great economic losses in marine and continental aquaculture species. Currently, several aspects of the clinical signs and pathogenesis of this Gram-negative bacterium have been described; however, determination of an appropriate reference gene is essential to normalize cellular mRNA data remain unknown. Here we evaluate the stability of seven candidate reference genes to be used for data normalization during ex vivo and in vivo experiments conducted in Atlantic cod, Atlantic salmon, and lumpfish. To assess this, raw Ct values obtained were evaluated by using geNorm, NormFinder, BestKeeper, Delta Ct comparison, and the comprehensive ranking, through the bioinformatic open-access portal RefFinder. We determined that fabD and era were most suitable reference genes in Atlantic cod primary macrophages, hfq and era in Atlantic salmon primary macrophages, rpoB and fabD in lumpfish head kidney samples, and hfq and era in lumpfish spleen. Our study demonstrates that use of multiple reference genes and its validation before measurements helps to minimize variability arising in qPCR studies that evaluate A. salmonicida gene expression in fish tissues. Overall, this study provided with an expanded list of reliable reference genes for A. salmonicida gene expression using qPCR during fish infection studies. • Here, we evaluated seven A. salmonicida reference genes for qPCR infection assays ex vivo and in vivo.. • fabD and era showed the most stable expression in Atlantic cod macrophages. • In Atlantic salmon macrophages infected with A. salmonicida , hfq and era were the most stable reference genes. • rpoB and fabD in lumpfish head kidney samples, and hfq and era in lumpfish spleen, were the most stable genes. • This study provided a reliable list of A. salmonicida reference genes for qPCR during ex vivo and in vivo infection. [ABSTRACT FROM AUTHOR]

The lumpfish ( Cyclopterus lumpus L.) has recently become relevant for aquaculture due to its appetite for the ectoparasitic copepod, the sea louse ( Lepeophtherius salmonis Krøyer). In order to determine the effect of temperature on growth properties of juvenile lumpfish, two size groups (6.2 g, S.E. ± 0.1 and 26.5 g, S.E. ± 0.6) were compared in terms of temperature- and size-related growth at 4, 7, 10, 13, 16 °C and varying ambient temperature. The overall highest growth rates were observed for fish < 120 g at 13 and 16 °C (3.65 and 3.60% day − 1 ), and declined stepwise with decreasing temperature. Only a modest response to temperature was observed for large fish > 120 g. Size rank correlations increased with increasing body weight. The results presented in this study suggest that optimum temperatures for growth (T optSGR ) decreased with increasing fish size from 15.7 °C for 11.0–20.0 g fish, 16.1 °C for 20.0–40.0 g fish, 13.1 °C for 100.0–110.0 g fish, to 8.9 °C for 120.0–200.0 g fish. [ABSTRACT FROM AUTHOR]

Growth and performance of Atlantic salmon in the presence of lumpfish were assessed in two studies. In the first study, six sea cages (5 × 5 × 5 m) were each stocked with 120 Atlantic salmon with a mean (± SD) weight of 619 (± 49) g and reared for 159 days. Control cages were without lumpfish, while two of the cages were stocked with 12 lumpfish (10% density), and two with 18 lumpfish (15% density) with a mean (± SD) weight of 54.0 (± 7.2) g. The lumpfish were removed from the cages after 56 days, but feed consumption and growth of the salmon were monitored for another 12 weeks until 17 November 2012 to investigate possible long term effect from the presence of lumpfish on growth performance of the salmon. In the second study, six sea cages (5 × 5 × 5 m) were each stocked with 80 Atlantic salmon with a mean (± SD) weight of 2400 (± 220) g and reared for 60 days. Two of the cages were further stocked with 4 lumpfish (5% density), and two with 8 lumpfish (10% density) with a mean (± SD) weight of 360 (± 30) g. Two cages without lumpfish acted as controls. In both studies sea lice infestation levels were recorded every other week. In the study with small salmon and lumpfish, the presence of lumpfish did not have any negative short- or long-term effects on feed conversion ratio (FCR) or specific growth rate (SGR) in salmon. However, when large salmon were reared together with large lumpfish, FCR was lower and SGR higher in the control cages compared to the two lumpfish treatments. Significantly lower sea lice infection levels were seen on Atlantic salmon when reared together with small lumpfish compared to the control group without lumpfish, whereas this trend was not as clear when reared with larger lumpfish. [ABSTRACT FROM AUTHOR]

The salmon louse is an ectoparasitic copepod that causes major economic losses in the Atlantic salmon aquaculture industry. To assess the efficacy of lumpfish grazing on attached sea lice on Atlantic salmon, six sea cages (5×5×5m) were each stocked with 120 Atlantic salmon with a mean±SD weight of 619±49g. Two of the cages were further stocked with 12 lumpfish (10% density) and two with 18 lumpfish (15% density) with a mean±SD weight of 54.0±7.2g. Two cages without lumpfish acted as controls. Sea lice infestation levels were recorded every other week for 54days. To determine the diet preferences of lumpfish in the cages, gastric lavage was performed every 2weeks. No differences in salmon or lumpfish growth between test groups and controls were observed. There were clear signs of lumpfish grazing on sea lice, with significantly lower average numbers of pre-adult, mature males and females stages of Lepeophtheirus salmonis per salmon. Lumpfish reduced the mature female stage of L. salmonis to levels equal to or lower than the counts recorded prior to the start of the study. There were no significant differences between the treatments (10% and 15% densities) in grazing efficacy. There was clear evidence of grazing from the results of gastric lavage, with 28% of all lumpfish found to have ingested sea lice on the last sampling day. Overall, the present results indicate that lumpfish is a suitable cold-water option for biological delousing of Atlantic salmon. [ABSTRACT FROM AUTHOR]

The production of lumpfish (Cyclopterus lumpus) is increasing rapidly due to their use as a cleaner fish for sea lice infections in Atlantic salmon farming. The sustainable development of captive broodstocks is reliant on good egg quality however this remains unknown. The present study assessed the hatching success and nutritional composition of eggs collected from two wild groups, at the start and end of the Norwegian fishing season (2018–2019), and one captive broodstock population (2019). Eggs from the farmed broodstock, used in this study, showed significantly lower fertilisation rates, eyeing rates and survival to hatching than eggs from wild broodstock. There was significantly less overall lipid content in the captive eggs when compared to the wild group as well as significantly lower levels of lipid fractions such as total N-3 PUFAs, minerals such as sodium and phosphorus and overall egg pigment levels. A principal component analysis of all 139 measured nutritional components within fatty acids, minerals and pigments was conducted to identify those associated with egg quality in lumpfish. A total of 51 components was identified as being positively (31) and negatively (20) correlated with hatching rate including essential fatty acids such as EPA, DHA and ARA, total pigment levels and calcium levels. Overall, this study clearly showed a reduction in egg quality from captive broodstock and suggested nutritional deficiencies in the current broodstock diets. As such, this study provides a foundation for further work into the optimisation of lumpfish broodstock management with a number of nutritional factors to be further investigated. • Captive egg hatching success in this study was significantly lower than the wild eggs. • 48 nutritional components correlated with hatching success including EFA's EPA, DHA and ARA. • Total pigment levels of lumpfish eggs correlated positively with hatching success. • Calcium and Nickle both correlated with hatching success. [ABSTRACT FROM AUTHOR]

The use of cleaner fish is an environmentally-friendly approach to combat the salmon louse, threatening commercial salmon farming. Dynamic Energy Budget (DEB) modelling helps understand the bioenergetics of early life stages of the cleaner fish, and can thereby aid optimisation of their culturing. Here, we report on our attempts to parametrise DEBkiss models for the yolk-feeding stages of two cleaner fish species, ballan wrasse (Labrus bergylta) and lumpfish (Cyclopterus lumpus). A range of measurements was taken over early development, including biometry (using imaging), weight and composition, as well as measurements of respiration rate. Despite the previous success of applying the DEBkiss model to early life stages of Atlantic cod, the model failed to capture the patterns of yolk depletion for ballan wrasse. The main issues were related to substantial changes in the water content of both yolk and structure over development, and a stop of growth before disappearance of the yolk sac. These issues require further experimental work to address, especially more efficient proxies for the dry mass of yolk and structure, such that these compartments can be efficiently separated. Nevertheless, apart from the pattern of yolk depletion, the model provides a reasonable explanation of all traits simultaneously. This indicates that model modifications may only need to be minor. For lumpfish, the data set was quite limited for testing of the DEBkiss model, due to the opacity of the egg and the fact that there was only one time point with measurements post hatch. Nevertheless, the data are consistent with the model. The modelling results indicate that both cleaner-fish species may have very similar bioenergetic parameters (and quite similar to Atlantic cod as well); the conspicuous difference in early life history may be mainly caused by the larger yolk provisioning in the egg, and late hatching, in lumpfish. The DEBkiss model is a simple and promising tool for bioenergetics of fish early-life stages. However, its application and in-depth testing is currently limited by the difficulties of obtaining detailed measurements on these life stages. • A simple, generic, energy-budget model was tested on fish embryo development. • Experiments were conducted for cleaner fish species: ballan wrasse and lumpfish. • The model performed reasonably but fails to capture the pattern in yolk depletion. • Specific areas for further work (both modelling and experimental) are proposed. [ABSTRACT FROM AUTHOR]

Lumpfish is now the single most important cleaner fish species to date and there is an extensive lumpfish translocation along the Norwegian coast. A reliable baseline information about the population genetic structure of lumpfish is a prerequisite for an optimal managing of the species to minimize possible genetic translocation and avoid possible hybridisation and introgression with local populations. The current study is a follow up of the study of Jónsdóttir et al. (2018) using expressed sequence tag-short tandem repeats (EST-STRs) markers. Samples (N = 291) were analysed from six sample locations along the Norwegian coastline from south to north, with additional 18 samples of first-generation (from wild fish) reared fish from a fish farm outside Tromsø (North Norway). Present findings show a lack of population differentiation among lumpfish sampling population along the Norwegian coast using EST-STRs, which is in accordance with the findings of Jónsdóttir et al. (2018) where genomic STRs (g-STRs) were analysed. Present findings indicate that should translocated lumpfish escape from salmon sea pens in Norway, this will probably have little impact on the genetic composition of the local lumpfish population. • Lumpfish is now the single most important cleaner fish species to date. • It is imperative that their use is done with the aim of minimizing possible genetic translocation. • Population genetic survey of stocks of lumpfish along the Norwegian coast was performed. • Lack of population differentiation was found indicating little effect of translocated lumpfish escapees. [ABSTRACT FROM AUTHOR]

Abstract: By-catch arising in the period May–November 2003 in the Icelandic blue whiting fishery was analyzed by random collection of 450 catch samples selected from 42 trips (9.4% of the total). By-catch species in the samples were quantified and their length measured. In general, by-catch was a relatively rare occurrence, but associated with rather wide confidence limits. Saithe and silver smelt were recorded in 21.1% and 19.1% of samples, respectively. Their total by-catch was 1605 and 1188t, respectively. Lumpfish, cod, golden redfish and deepwater redfish were recorded in 2.2–5.6% of samples, and their total by-catch was 30–156t by species. The remaining five fish species were recorded in &#60;1% of samples, and their total by-catch was 6t or less by species. In addition, unidentified cephalopods were recorded in 1.8% of samples with a total by-catch of 31t. Spatial distributions of the main species indicate that saithe and silver smelt are primarily caught in Faroese, but cod and lumpfish in Icelandic waters. Length distributions indicate that the by-catch mainly constitutes the catchable component of the stocks in question. In terms of the effect of the by-catch on fish stocks, the main concerns are with saithe and lumpfish. There are indications that by-catch of cod and saithe in 2003 may have been at a relatively low level in a longer-term perspective. [Copyright &y& Elsevier]

This paper describes the use of lumpsucker (Cyclopterus lumpus) otoliths for age determination, with focus on methods that were found practical, the precision achieved in the first documented age-reading workshop of this species, and comparisons with length composition of the stock. The otoliths are very small and special training is necessary to locate them. The zonation pattern is relatively distinct and it was usually easy to establish a set of rings assumed to be annuli. The precision of age estimates was reasonably high for ages 1–4, although no formal verification was available at the time of reading. After the workshop, the resulting age–length relationship was compared to new estimates of length composition of juvenile lumpsucker prior to and after the migration from the coast. This supported the applied reading method. The age estimates together with length frequencies from the spawning ground suggest that males may spawn for the first time at age 2–3, and females at age 3–4. This is at least 1–2 years less than all previous estimates of age at maturity. However, further verification (e.g., by tracing the edge properties throughout the year) should be done before age-structured data are used in assessments of this species. [Copyright &y& Elsevier]

Infestations by the salmon louse (Lepeophtheirus salmonis Krøyer) represents the major fish health problem that the Atlantic salmon (Salmo salar) industry has to face. Sea lice infestation has a large impact on the economy of fish farmers, which are looking for a cost-effective and environmentally sustainable alternative to chemical or mechanical treatments to delouse fish. The biological control of sea lice using the so-called cleaner fish has been individuated as a feasible delousing approach of Atlantic salmons. In particular, in recent years the lumpfish (Cyclopterus lumpus) has been extensively farmed to be used as a 'biological weapon' in salmon farming because of its effectiveness in delousing also in harsh environmental conditions. However, the environmental impact of lumpfish farming is still largely unknown. Thus, the present study aimed at assessing the potential environmental impact of lumpfish production through a life cycle assessment (LCA) approach. Feed and electricity consumption, both for 8 of the 18 evaluated midpoint indicators, are the main responsible of the environmental load while for the Freshwater and Marine eutrophication about 90% of the impact is related to the emission of nitrogen and phosphorous compounds by fishes. These data lay the foundation for further, sustainable improvement of lumpfish farming. • Environmental impact of lumpfish farming was assessed through LCA. • Feed and electricity consumption were the main contributors of environmental impact. • Emission of nitrogen and phosphorous were found as contributors of eutrophication. • These data can contribute to improve sustainability of lumpfish farming. [ABSTRACT FROM AUTHOR]

Lumpfish are currently produced and utilized as cleaner fish, to control sea lice infestation rates in salmon net pens, but information on environmental requirements is still limited. This study aimed to determine the zone of environmental hypoxia for two relevant fish sizes (15 and 60 g) and temperatures (5 and 12 °C), using intermittent flow respirometry (referred to as 15:5, 15:12, 60:5, 60:12), and to investigate parameters of stress in response to acute changes in dissolved oxygen (DO, % air saturation) from normoxia to 47, 63, 98 (control), 148 and 194% O 2 at 10 °C. The standard and maximal metabolic rates (SMR and MMR) were measured in normoxia (n = 8), and MMR was measured at 5–6 DO levels ranging from 20 − 160% O 2 (n = 8 per DO) to define the upper and lower boundaries of the hypoxic zone (DO lim and DO crit). SMR, MMR and the aerobic metabolic scope (AS) increased with temperature and decreased with fish size. Similar effects of temperature and size were found on DO crit – DO lim ranges: 20–55 (15:5), 35–147 (15:12), 21–53 (60:5) and 22–89 (60:12) % O 2 air saturation. Results from acute exposure tests resulted in elevated cortisol levels at 63 and 47% O 2 , although not statistically significant at 47% O 2. Other parameters of hypoxic or hyperoxic stress (lactate, pH, osmolality, lipid peroxidation rates, catalase activity) were not affected. Results from the present study suggest that lumpfish may experience oxygen levels in sea cages that restricts metabolism, performance and induce hypoxic stress. • The zone of env. Hypoxia (ZEH) was studied in 15 and 60 g lumpfish at 5 and 12 °C. • Interactive effects of temp. and size on ZEH boundaries (DO crit /DO lim) were found. • DO crit ranged from 20 to 35% O 2 , DO lim ranged from 53 to 147% O 2. • Increased plasma cortisol was observed in moderate, acute hypoxia (63% O 2). • Oxidative stress was not observed in moderate, acute hyperoxia (148 and 194% O 2). [ABSTRACT FROM AUTHOR]

Lumpfish (C. lumpus) are used as cleaner fish in the Atlantic salmon (Salmo salar) farming industry to remove parasitic sea lice. At present, wild lumpfish broodstock are used which puts strain on wild populations. By successfully cryopreserving lumpfish sperm, the number of wild males required will be reduced and it enables the long-term storage of sperm for use in breeding programmes. The present study compared the use of fresh sperm and sperm which was cryogenically frozen for 24 h to test whether it is a viable method of preservation. The fresh and frozen sperm from 5 males was used (in equal volumes) to fertilize eggs pooled from 5 females and the difference between fertilization success, percentage of eggs which reached the eyed stage, and the hatching success was measured. A group of 100 hatched larvae were on-grown for two weeks to test whether there was a difference weight between treatment groups. The results of the trial showed that fresh sperm produced a significantly higher percentage of fertilized eggs (fresh 92.6 ± 0.8%, frozen 77.9 ± 1.8%, mean ± SEM), a higher percentage of eggs surviving to the eyed stage (fresh 93.9 ± 0.5% and frozen 80.8 ± 1.4%) and had a more successful hatch rate (fresh 72.3 ± 6.6% and frozen 63.6 ± 5.0%). There was no difference in mean weight (± SEM) of the two-week old larvae between treatments (fresh 0.63 g ± 0.024, frozen 0.59 g ± 0.028). In conclusion, this study showed that the same volume of cryogenically preserved lumpfish sperm produced fewer viable lumpfish larvae than fresh sperm. Despite this difference, the use of cryopreserved sperm did produce relatively high results at each stage of testing. • Cryopreserved and fresh sperm quality was tested in lumpfish. • Fresh sperm produced a significantly higher percentage of fertilized eggs (fresh 92.6% vs. frozen 77.9%). • Fresh sperm produced a higher percentage of eggs surviving to the eyed stage (fresh 93.9% vs. frozen 80.8%). • Fresh sperm had a more successful hatch rate (fresh 72.3% vs. frozen 63.6%). • No difference was found in larval growth two weeks after hatching. [ABSTRACT FROM AUTHOR]

First interaction with carnivorous clients induces stress responses even in the boldest of cleaner fishes observed in nature. This is relevant for the expanding use of lumpfish in aquaculture, where stress could impede the species ability to interact with Atlantic salmon. The study investigated how naive lumpfish (34.3 g, S.D. ± 6.48) responded to different heterospecific cues including (1) exposure to water from a tank with Atlantic salmon ("Olfaction"), (2) salmon lifelike models ("Model") and (3) Atlantic salmon ("Live"). Experiments were repeated thrice, using duplicate tank replicates on each occasion (n = 36 per treatment). Behaviour was recorded 30 min before and 30 min after the introduction of each treatment. Responses measured included swimming activity, body colour and pigmentation, neurotransmitters, and plasma cortisol. Data demonstrated a significant increase in swimming activity upon introduction of Olfaction and Live salmon, but not from Models. After 30 min of interaction, swimming activity decreased towards levels observed in control groups. Body colour significantly increased in lumpfish exposed to Olfaction while body pigmentation significantly increased in both Olfaction and Model treatments. Neurotransmitters and plasma cortisol measurements did not differ between treatments and control, yet large individual variation was observed. Our findings revealed that lumpfish discriminated salmon cues, whereas Olfaction induced the overall strongest behavioural and physiological responses. The study suggested that acute change in skin colour and pigmentation can be impacted by salmon interaction, yet deployment of naive juvenile lumpfish with small Atlantic salmon is preferable based on the overall mild stress responses. • Lumpfish acute responses to salmon cues (live, olfaction and models) were studied. • Olfaction and live salmon affect lumpfish swimming activity more than models. • Olfaction and models impact skin colour and/or darkening. • Atlantic salmon body size influence activation of the HPI axis in lumpfish. [ABSTRACT FROM AUTHOR]

To investigate the possible family influence on sea lice grazing of lumpfish on Atlantic salmon, ten families of lumpfish (N = 480) with a mean (± SD) weight of 54.8 ± 9.2 g were distributed among ten sea cages (5 × 5 × 5 m) each stocked with 400 Atlantic salmon with a mean (± SD) weight of 621.4 ± 9.2 g. All the ten cages were stocked with 48 lumpfish (12% stocking density). The stocking of cages was such that each cage consisted of two random families where full- and paternal half-sib families were randomly allocated to the different cages. There were clear differences in sea lice grazing efficacy, growth and cataract prevalence between the ten families assessed in this study. Lumpfish from families 2, 6 and 10 had the lowest mean weights but showed comparable growth rates compared to the other families throughout the study and this may be as a direct result of genetic influence. In addition, fish from these families had a significantly higher incidence of lice grazing of both L. salmonis and C. elongatus compared to the other families. Using mixed linear model to analyse the data revealed significant family and paternal effect on sea lice grazing. There was a trend for a reduction in sea lice grazing with increased size within each family. The results indicated that it was the smallest size classes of lumpfish (40–140 g) which exhibited higher sea lice grazing potential compared to the larger size classes within families. There were no clear differences in the lice grazing potential between male and female lumpfish within and between families. Overall, present findings showed that sea lice grazing of both L. salmonis and C. elongatus can be enhanced using targeted family production and if this behaviour has a genetic basis it may further enhanced through selection and targeted breeding programs. • We assessed the possible family influence on sea lice grazing of lumpfish on Atlantic salmon. • There were clear differences in sea lice grazing efficacy, growth and cataract prevalence, between the families assessed. • No clear differences in the lice grazing potential between male and female lumpfish within and between families was found. • Smallest size classes of lumpfish (40–140 g) exhibited higher sea lice grazing potential within families. [ABSTRACT FROM AUTHOR]

In the last decade, the salmon aquaculture industry has considerably increased the use of lumpfish juveniles as cleaner fish. Potential escape of reared lumpfish into the wild may spread diseases or genetically contaminate wild stocks. The guidelines for minimum sizes of cleaner fish to use in aquaculture cages are currently based on simple mesh penetration tests. However, these guidelines do not consider the potential compressibility of fish or changes in mesh state due to factors such as sea conditions and maintenance operations. This study shows that the industry-recommended minimum stocking sizes for a given mesh size may result in escape risk and that ignoring fish compressibility and mesh state can lead to underestimation of the lumpfish sizes that are able to escape. Our results can be used to develop new guidelines that will contribute to reduced escape of lumpfish from salmonid farms and lessen the potential environmental consequences. Unlabelled Image • The salmon aquaculture industry uses reared lumpfish juveniles as cleaner fish. • Escape of reared lumpfish may spread diseases or genetically contaminate wild stocks. • Ignoring mesh state can lead to underestimation of the lumpfish sizes that can escape. • Provided guidelines contribute to reduced escape of lumpfish from salmonid farms. [ABSTRACT FROM AUTHOR]

There is increased commercial interest in the production of lumpfish (Cyclopterus lumpus) as a biological control against sea lice infections in Atlantic salmon farming. To ensure a sustainable supply of lumpfish, reliable captive reproduction is required however, optimal husbandry and conditions for captive broodstock performance remain unknown. Artificial fertilisation of gametes remains the preferred management strategy for lumpfish, but this requires an effective milt management protocol. The present study tested several milt extender solutions for short term cold storage and validated sperm concentration assessment of lumpfish milt. Results demonstrated lumpfish sperm has a long motility survival time (motile for up to 3 h) when compared to other marine teleosts. Importantly, all extenders used in the study were non-activating on dilution of the milt. Lumpfish milt was successfully stored at 4 °C in Modified Turbot Extender (MTE), Herring Ringers Solution and Aquaboost SpermCoat (Cryogenetics, Norway) for up to 14 days post stripping. MTE performed more effectively with regards to maintenance of sperm activation time in comparison to the other tested extenders. There was a significant positive correlation between sperm concentration identified through cell counts using a haemocytometer and both packed cell volume (spermatocrit) and measured optical density at 640 nm (r2 = 97.42 ± 2.14). This suggests both packed cell volume and spectrophotometric measurements can be effective methods for rapidly assessing sperm concentration in lumpfish. This study validated several options for quantifying sperm concentration and short-term cold storage of lumpfish milt that can be used for hatchery management in lumpfish aquaculture. • Lumpfish sperm is motile for >3 h. • Lumpfish milt can be stored for 14 days when diluted in extender solutions • Modified Turbot Extender was the most effective extender at 1:5 milt to extender ratio • Significant relationship exist between sperm counts, spermatocrit and optical density [ABSTRACT FROM AUTHOR]

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. • Cleaner fish were held in stratified salmon production sea cages over autumn-winter. • Ballan wrasse did not grow, while lumpfish displayed considerable growth. • High losses were observed in both ballan wrasse (57%) and lumpfish (27%). • Losses may cause low long-term effectiveness of cleaner fish as biological controls. • Lumpfish occupied shallower, cooler and less saline water than ballan wrasse. [ABSTRACT FROM AUTHOR]

To investigate possible differences survival and welfare of lumpfish fed either feed blocks or commercially available pelleted feed in commercial cages, eight 90 m polar circle cages containing approximately 50,000 Atlantic salmon with a mean weight of 2 kg were stocked with 3800 lumpfish with a mean weight of 52 g in each cage. Four of the cages were fed with a standard commercial pelleted feed and four with feed blocks. Growth was significantly lower for fish fed feed blocks although both feed types were offered at a daily feeding rate of 1.5% BW−1 based on biomass gain. There were differences in the number of mortalities recorded between the two treatments with fish fed with pelleted feed had higher mortality and was more sensitive towards mechanical treatment that occurred during the study period. Operational welfare indictors (OWI) were developed to assess health and condition for lumpfish. The OWIs showed a lower score in the feed block group indicating better health status in this group. Overall, the findings of the present study show that feed blocks can give more controlled growth, increased survival and better overall health status of lumpfish in sea pens with Atlantic salmon. • We assessed the effect of food blocks on growth, survival and welfare of lumpfish in large sea cages. • Feeding with food blocks improved survival and health of lumpfish. • Fish feed conversional pelleted feed was more sensitive towards mechanical treatment. • An operational welfare index (OWI) was developed to assess health and condition for lumpfish. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Lumpfish (Cyclopterus lumpus L.) in Norway is currently produced in traditional flow-through systems (FTS). Hatcheries frequently show signs of bacterial infections, unstable microbial communities in the rearing water and varying mortality. Recirculating aquaculture systems (RAS) is proposed to create stable and healthy microbial environments, with less probabilities for blooming of opportunistic microbes. Studies have also shown that RAS increases the survival of marine fish. The aim with this study was to investigate the effect of various RAS water treatment designs on water and biofilm microbiota, survival, growth and gill health of lumpfish. An experiment with lumpfish was conducted, from 2 months post hatch to the transfer into sea cages. Five different water treatment regimens were compared: 1. RAS with no additional water treatment, 2. RAS with a filtration unit for removal of small particles, 3. RAS with filtration and disinfection with UV-irradiation, 4. RAS with filtration and disinfection with UV-irradiation and ozone and 5. FTS as a reference. The microbiota of the rearing water and tank wall biofilm were sampled and characterized by Illumina sequencing of 16S rDNA amplicons. Lumpfish juveniles reared in the RAS treatments were exposed to a more stable and diverse rearing water microbiota, with a lower share of opportunistic bacteria, a probable reason for the higher survival and better gill health of the fish compared to siblings reared in the FTS. Lumpfish reared in RAS without disinfection were exposed to a more diverse and stable water microbiota, with a lower share of opportunistic and potential harmful bacteria, compared to the lumpfish reared in RAS with disinfection and FTS. This resulted in better gill health. Fish in RAS with filtration, but no disinfection, had a better gill health than the fish in the RAS without filtration, possibly due to the reduction of small particles. The lumpfish were exposed to different microbial communities of both water and biofilm, due to the different treatments of the incoming tank water. In conclusion, our results indicate that implementation of RAS in the production of lumpfish has a potential to increase both survival, growth and gill health of the fish and that RAS with filtration of small particles, but without disinfection, result in the best fish health and performance among the investigated treatments. • We managed to increase survival, growth and health of lumpfish by implementing RAS. • Disinfection in the RAS loop affected the microbiota and the gill health negatively. • Filtration of small particles improved gill health of lumpfish. [ABSTRACT FROM AUTHOR]