The Three‐spined Stickleback,Gasterosteus aculeatus Linnaeus 1758, plays a minor role as a host of Lepeophtheirus salmonis (Krøyer 1837) in the Gulf of Maine

The sea louse, Lepeophtheirus salmonis (Krøyer 1837), is a significant parasite of farmed salmon throughout the Northern Hemisphere. Management of on‐farm louse populations can be improved by understanding the role that wild fish play in sustaining and providing refuge for the local population of sea lice. In this study, 1,064 sticklebacks were captured. Of these animals, 176 individuals were carrying a total of 238 sea lice, yielding a prevalence and intensity of 16.5% and 1.4 lice per fish, respectively. Detailed examination of the sea lice on the three‐spined sticklebacks captured in Cobscook Bay found two L. salmonis individuals using three‐spined sticklebacks as hosts. A 2012 survey of wild fish in Cobscook Bay, Maine, found multiple wild hosts for Caligus elongatus (von Nordmann 1832), including three‐spined sticklebacks (Gasterosteus aculeatus L.), but no L. salmonis were found in this earlier study.     

The duration of efficacy following oral treatment with emamectin benzoate against infestations of sea lice,Lepeophtheirus salmonis (Krøyer), in Atlantic salmon Salmo salar L.

The duration of efficacy of emamectin benzoate in the oral treatment of sea lice, Lepeophtheirus salmonis, infesting Atlantic salmon, Salmo salar L., was evaluated in a tank study. One group of salmon was treated at a nominal dose of 50 μg kg?1 biomass day?1 for 7 consecutive days and a second group was untreated. Fish were then redistributed to 16 tanks, each holding 17 control and 17 treated fish. On days 34, 41, 48, 55, 62, 69, 76 and 83, two tanks were challenged with L. salmonis copepodites. Eight to 14 days after each challenge, fish were anaesthetized and numbers of lice recorded. Treatment with emamectin benzoate prevented development of copepodites for up to 62 days from the start of treatment, and chalimus numbers remained low for 69 days. Treated fish, challenged from days 34 to 69, had significantly (P<0.01) fewer lice than control fish. Treated fish challenged at days 76 and 83 still had fewer lice than control groups, although differences were not statistically significant for both replicates. When chalimus appeared on treated fish challenged at days 69–83, survival of chalimus to adult stages was lower than on control fish. Louse egg production on treated fish challenged at days 62–83 was not reduced compared to control groups.     

Efficacy of teflubenzuron (Calicide®) for the treatment of sea lice, Lepeophtheirus salmonis (Krøyer 1838), infestations of farmed Atlantic salmon (Salmo salar L.)

The efficacy of teflubenzuron (Calicide^®) for the treatment of farmed Atlantic salmon (Salmo salar L.) infested with sea lice [Lepeophtheirus salmonis (Krøyer)] was investigated on two commercial salmon farms. Teflubenzuron (Calicide^®) coated onto commercial feed pellets was administered orally at 10 mg per kg body weight per day for seven consecutive days. Fish were randomly sampled and lice numbers recorded from both treated and control groups on four sampling occasions post‐medication. Statistically significant reductions in the number of L. salmonis per fish were recorded. Maximum efficacy was observed toward chalimus and preadult stages of L. salmonis, and was achieved about 7 days post‐medication. No apparent effect was observed on adult lice. No adverse drug reactions or palatability problems were associated with the treatments.     

A comparison of epidemiological patterns of salmon lice, Lepeophtheirus salmonis, infections on farmed Atlantic salmon, Salmo salar L., in Norway and Scotland

This paper examines two large national data sets collected over several years and contrasts the patterns of sea lice, Lepeophtheirus salmonis (Krøyer, 1837), infections, the use of treatments and the occurrence of chalimus peaks between Norwegian and Scottish farms. Infection levels in Scotland were significantly higher in general over the period under study. For the chalimus stage group in the first quarter of the year, Norwegian mean abundance stayed below 10 lice per m² while Scottish means reached 45 lice per m² of fish skin per m³ of water. Both countries had more chalimus in summer than at other times of year, but in the last 3 months of the year Scottish fish had, on average, two to four times as many chalimus as Norwegian fish. Peaks of chalimus abundance were more frequent in Scotland, particularly in winter, but the most prominent peaks occurred in summer in both countries. In Scotland a marked mid-year build-up of mobile pre-adult and adult stages was seen, and both countries showed a tendency for mobile counts on the second year fish to increase towards the end of the year. Scottish fish carried, on average, three times as many mobile lice per m² of skin as Norwegian fish in the last 3 months of the year. The difference in lice loads was reflected in the greater use of veterinary medicines on Scottish farms. The higher infection levels in Scotland may be due to shallower and more enclosed water bodies used for farming, smaller and shallower pens, differences in sea water temperatures or in access to appropriate medication. The results highlight the importance of ensuring that effective veterinary medicines are available in the UK for the control of infection.     

Does the AquasmartTM feeding system reduce sea louse [Lepeophtheirus salmonis (Krøyer)] infestation on farmed Atlantic salmon (Salmo salar L.) in winter?

Infections of sea lice [Lepeophtheirus salmonis (Krøyer)] were studied over winter on a working, commercial salmon farm in relation to two types of feeding system: a regular, pneumatic spray feeder and an irregular, ‘demand feed’ sensor system (Aquasmart^TM). Contrary to prediction, the Aquasmart^TM system alone had no significant effect on chalimus infestation compared with fish fed by pneumatic spray. However, it was associated with significantly reduced numbers of mobile stages, both at the beginning of the study (P < 0.05) and, more particularly, in conjunction with treatment of all pens using hydrogen peroxide (P < 0.001). It is suggested that feeding regime may represent a useful tool in reducing lice infestation when co‐ordinated with other methods of control, such as peroxide treatment, and that further work in this field is merited.     

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

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

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

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

Resistance of sea lice, Lepeophtheirus salmonis (Krøyer), to hydrogen peroxide on farmed Atlantic salmon, Salmo salar L.

Hydrogen peroxide has been the only medicine used to treat salmon infected with sea lice [Lepeophtheirus salmonis (Krøyer)] on many farms in Scotland since 1992 and reports have suggested reduced treatment efficacy. The present study tests the sensitivity of sea lice to exposure to hydrogen peroxide under farm conditions and also in vivo by comparing lice from a farm with suspected resistance and lice from a farm that had not been pre‐exposed to hydrogen peroxide. In bin treatments on fish from a farm treated with hydrogen peroxide on 41 occasions, numbers of ovigerous lice declined by only 15% and 16% in two replicates and other mobile stages by 25%. Where hydrogen peroxide had not been used, ovigerous females declined by 90% and 87% and other mobile lice stages by 97% and 99%. These trials and observed poor efficacy of cage treatments, for example only 7.5% reduction in lice numbers when fish were treated with 2000 p.p.m. for 20 mins, indicated resistance of lice to hydrogen peroxide. The mechanisms involved in the development of resistance, possible genetic selection for lice with reduced carapace permeability or detoxifying enzymes such as catalase, or tolerance through induction by subtherapeutic exposure are reviewed. Implications for lice control strategies relying on hydrogen peroxide are discussed.     

Laboratory and field investigations of salmon lice [Lepeophtheirus salmonis (Krøyer)] infestation on Atlantic salmon (Salmo salar L.) post-smolts

Hatchery‐reared 1‐year‐old Atlantic salmon post‐smolts (Salmo salar L.), artificially infected with salmon lice [Lepeophtheirus salmonis (Krøyer)] copepodids, were found to suffer from primary alterations (increased cortisol levels) at early lice stages. Secondary alterations, such as osmotic stress (increased chloride levels), first occurred after the preadult stages of the lice appeared. Fish with the highest salmon lice infections died throughout the experiment. Seven years of field investigation of Trondheimsfjorden showed that Atlantic salmon post‐smolts descending coastal waters can become heavily infected with salmon lice. The migrating post‐smolts were only infected with the chalimus stages, showing that the fish had only recently left the rivers. The infection level, however, varied considerably between the years, and, in 1998, the infection was higher than previous years. The experimental results have been combined with the field data to appraise the consequences of the infection.     

Glochidial infestation of fish by the endangered thick‐shelled river mussel Unio crassus

相似文献   

The Physical Condition and Welfare of Five Species of Wild‐caught Wrasse Stocked under Aquaculture Conditions and when Stocked in Atlantic Salmon,Salmo salar,Production Cages

Several indices were examined to assess the physical condition of wrasse stocked on Atlantic salmon, Salmo salar, farms as cleaner fish, and included examination of eye condition, snout erosion, skin hemorrhaging, and erosion and splitting of dorsal, pectoral, anal and caudal fins. Baseline values were determined for five wrasse species: goldsinny, Ctenolabrus rupestris; rock cook, Centrolabrus exoletus; corkwing, Crenilabrus melops; cuckoo, Labrus mixtus; and ballan, Labrus bergylta, held in a farm environment for 3 mo prior to transfer to salmon farms. The caudal fin was most affected by injury. The fin erosion index (FEI) was low in all species and below 0.6. The fin splitting index (FSI) was the most prominent index and was significantly higher in the caudal fin (FSI > 2) compared with other fins (FSI < 0.5), and also significantly higher in corkwing and rock cook compared with the other wrasse species. The FEI and FSI were also calculated for a group of ballan wrasse before stocking on a seawater farm, during the first winter and upon harvesting. There were no significant differences in the scores of fin erosion and fin splitting in any of the samples, although the indices were marginally poorer in winter.     

Differences in Lepeophtheirus salmonis abundance levels on Atlantic salmon farms in the Broughton Archipelago, British Columbia, Canada

Sea lice data collected from Atlantic salmon farms in the Broughton Archipelago between 2003 and 2005 were examined for inter-regional differences in mobile Lepeophtheirus salmonis (Krøyer) abundance using the generalized linear model procedure. Factors such as age of the salmon populations, location of farms and time of year had a significant effect on the abundance of the mobile stages of L. salmonis whereas water temperature and salinity did not. Separate evaluation of SLICE® treatment data found no significant difference in treatment frequency among the areas but did show that there were significantly lower numbers of farm treatments during the summer months when compared with other seasons. The role of environment and wild fish in influencing sea lice abundance on the farmed salmon is discussed. The findings suggest that effective management programmes for sea lice should not only be based on geographical location but should take into account other factors which could influence lice abundance levels.     

Infestation parameters for Lepeophtheirus salmonis (Kroyer) (Copepoda: Caligidae) parasitic on sea trout, Salmo trutta L., off the west coast of Ireland during 1990 and 1991

Abstract. Infestation parameters for the calígíd copepod Lepeophtheirus salmonis (Kroyer) infesting sea trout, Salmo trutta L., were established for a number of locations off the west coast of Ireland during 1990 and 1991. Based on these parameters sites were classified into two groups in 1990 and three in 1991. Median parasitic intensity in these groups was 11·6 and 77 in 1990 and 9·5, 29·5 and 55 in 1991. Fish were parasitized mainly by chalimus stages of the parasite which attached preferentially to the fins. Heaviest infestations were invariably due to chalimus stages and early pre-adult lice and there was a progressive decrease in the correlation between parasitic intensity and the number of each successive stage in the life cycle. This suggested either host or parasite mortality as the parasite matured. Large numbers of lice-infested fish returned prematurely from the sea to estuarine areas at a number of sites. Extensive morphological damage, especially to the fins, was apparent on a proportion of these fish as a result of the infestation. Mortality of heavily infested fish was directly observed.     

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

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

Effect of Light Intensity on Color Performance of False Clownfish,Amphiprion ocellaris Cuvier

Color performance of false clownfish, Amphiprion ocellaris Cuvier, was examined under three levels of light intensity (20–50 , 600–850 , and 2700–3500 lx) for 5 wk. The experiment was conducted in nine rectangular glass aquaria (25 × 25 × 20 cm) with three replicates. Each aquarium was stocked with 36 fish, and 3 fish were randomly sampled from each aquarium every other week. Digital images were taken weekly on each individual fish after it was anesthetized in MS‐222. The color performance in hue, saturation, and brightness was quantified using image analysis. In addition to the whole‐body analysis, each fish image was divided into ventral and dorsal parts to assess the body position‐dependent effect. Furthermore, color differences between dorsal fin, anal fin, ventral fin, and caudal fin were also quantified. The whole body was brighter at low light than at medium or at high light intensity. Irrespective of light intensity, the dorsal side was more orange but less bright than the ventral side. Brighter light strengthened overall orange color on fish fins. The dorsal fin and ventral fins appeared more orange than the anal and caudal fins regardless of light intensity and exposure duration. Similar to body color, low light also led to brighter fins, especially for caudal and dorsal fins. Our results indicate that ambient light could regulate fish color performance but could not change the pigment dominance by β‐carotene. Light intensity is unlikely to change the contrast between dorsal and ventral sides, but dim light tends to make fish body brighter, and bright light strengthens orange color on fins.     

Time-series models of sea lice Caligus elongatus (Nordmann) abundance on Atlantic salmon Salmo salar L. in Loch Sunart, Scotland

Most lice infestations on salmon farmed in the North Atlantic are attributed to Caligus elongatus and Lepeophtheirus salmonis. This study reports findings from time‐series analysis conducted on observations of the lesser‐studied C. elongatus, in four farms on the west coast of Scotland over the period 1996–2000. Least‐squares and Poisson regression techniques were applied to one individual site and to the aggregated data of four sites. Models were fitted and tested for goodness of fit using appropriate statistical methods. Findings indicate that infestation levels are highly seasonal with rapidly increasing numbers after week 22 of the year followed by a steady decline from week 40. Abundance is much lower in the second year of the production cycle than the first. Neither of the models indicated that treatment application has a significant effect on C. elongatus infestations.     

Impact of Background on Color Performance of False Clownfish,Amphiprion ocellaris,Cuvier

Color performance of false clownfish, Amphiprion ocellaris, Cuvier was first examined at four color backgrounds (blue, green red, and white) for 4 wk, then all fish were transferred to a white background for another 4 wk to test whether the impact of background colors on fish skin could have a lasting effect when the environment colors are changed. The experiment was conducted in 10‐L rectangular plastic buckets with three replicates. Thirty fish were stocked in each bucket and three fish were randomly sampled from each tank in Weeks 1, 4, and 8. The color hue, saturation, and brightness were quantified using image analysis. In addition to the whole body analysis, each fish image was divided into ventral and dorsal parts to examine the body position‐dependent response. Furthermore, color differences among the dorsal fin, anal fin, ventral fin, and caudal fin were also quantified. Blue or green background enhanced red orange color on fish skin, whereas white background made fish color brighter. Irrespective of background color, the dorsal side of fish exhibited more red orange, but the color was less bright and less saturated than that of ventral side. Upper fins (dorsal and caudal fins) were more red orange in a blue background than in a white background. Transferring fish from colored backgrounds to a white background made the fish skin and fins brighter, the color of ventral body and ventral fins less saturated, and the bottom fins more yellow orange. The results indicate that blue or green background could strengthen the orange color, whereas white background made fish color less saturated but brighter. The impact of background on the performance of fish color is temporary and likely to disappear when environmental color changes.     

Genetic basis of pectoral fin deformities in the African catfish Clarias gariepinus (Burchell, 1822), Heterobranchus longifilis (Valenciennes 1840) and their hybrids

Morphological aberrations of the pectoral fins in nine mating combinations involving Clarias gariepinus (Burchell, 1822), Heterobranchus longifilis (Valenciennes, 1840) and their hybrids were investigated to determine the level and genetic basis of occurrence. The highest mean percentage survival in a Clarias× Clarias group was 75%, whereas the least mean percentage survival was 2% in the same group. The least mean percentage survival (40.3%) in the remaining three groups occurred in the cross of female hybrid (right pectoral fin absent) × male C. gariepinus (right pectoral fin absent). A maximum of nine types of aberrations was observed in the four mating groups – double dorsal fin, curved posterior dorsal fin, spineless right pectoral fin, right pectoral fin absent, left pectoral fin absent, rudimentary pectoral fin, both pectoral fins absent, double anal fin and curved anterior dorsal fin. These nine aberration types were recorded in the Clarias× Clarias group, with a total frequency ranging from 7.14% to 75.00%. The least number of aberrations was observed in the hybrid ×Clarias group (double dorsal fin and both pectoral fins absent) with a frequency range of 1.47–5.55%. No aberration was observed in two crosses involving female hybrid (right or left pectoral fin absent) × female C. gariepinus (normal). The level of aberrations in some of these crosses indicates the involvement of genotype rather than the influence of environment.     

The settlement and reproductive success of Lepeophtheirus salmonis (Krøyer 1837; Copepoda: Caligidae) on atypical hosts

The reproductive success of Lepeophtheirus salmonis settled on host and non‐host fish has been compared. Triplicate single species tanks of Atlantic salmon, marine three‐spined sticklebacks, saithe and Atlantic cod were exposed to 10 adult female L. salmonis per tank (n=30 lice per species). Adult female L. salmonis settlement and egg string production occurred only on salmon and cod, with no egg production occurring on saithe and three‐spined sticklebacks. The number of eggs in egg strings, hatching success of eggs and the survival of all larval stages to the copepodid stage were severely affected by the species of fish on which female L. salmonis had settled. L. salmonis settled on cod produced significantly fewer eggs, lower hatching rates and lower survival rates of larvae than females on Atlantic salmon. The production of egg strings by L. salmonis females infecting cod, which successfully hatch and moult through to the infective copepodid stage, albeit in small numbers, is discussed in terms of the implications to aquaculture and salmon and cod farming scenarios.     

Fin development in stream- and hatchery-reared Atlantic salmon

To determine the effect of development and environment on fin growth, we measured fin lengths of juvenile Atlantic salmon (Salmo salar) from two hatcheries (August, October and April–May), stream-reared fish (July and October) stocked as fry into two tributaries, and smolts from the main stem of the Connecticut River (May). For stream-reared parr, there was a linear relationship between the dorsal, caudal and anal fins with fork length, while the pectoral, pelvic and adipose fins exhibited a curvilinear relationship with fork length. Parr from a high gradient stream had larger caudal fins than fish from a low gradient stream, but other fins did not differ. Regression lines for the fins of stream-reared smolts were all linear when fin length was regressed against fork length. Stream-reared parr had larger pectoral, pelvic and anal fins than smolts of similar size while dorsal and caudal fin lengths did not differ. Regression equations formulated using the fins of stream-reared parr were used to calculate the percent difference (100×observed fin length/expected) in fin lengths between stream- and hatchery-reared parr. The pelvic, adipose, caudal and anal fins of hatchery-reared parr showed no signs of degeneration by the first sampling period 7 months after hatching, whereas degeneration in the pectoral (13–20%) and dorsal (15–18%) fins was evident at this time. By the end of the study, degeneration was present in every fin except the adipose, with the pectoral (35–65%) and dorsal (32–58%) fins exhibiting the greatest amount of fin loss. All fins of hatchery-reared parr became shorter with time. There were minor differences in fin degeneration among parr from the two hatcheries, but the overall pattern of decreasing fin size was similar, indicating a common cause of fin degeneration. Comparison of stream- and hatchery-reared fish is a valuable means of determining the impact of captive environments on fin growth.