Lice Counts Research Articles

Detachment and re-attachment of Salmon lice during full-scale delousing operations on Salmon farms

This study examined salmon lice (Lepeophtheirus salmonis) numbers during different full-scale lice treatments of salmon, with focus on detachment during crowding and re-attachment post-treatment. Data was collected from 259 non-medicinal treatments (NMM) during 2018 and 2019. The dataset included data from thermal (Optilicer), mechanical (Flatsetsund Engineering, SkaMik, Hydrolicer) and freshwater treatments. Salmon lice were counted by the staff at the aquaculture sites, and registered in the following categories: sessile, preadult/adult male (PA/AM) and adult female. A counting protocol was established in collaboration with staff from the aquaculture companies taking part, where the time for counting the parasitic salmon lice was: Sample 0: before crowding; Sample 1: at the end of the first crowding; Sample 2: during unloading of the salmon after treatment; and Sample 3: after delousing of the salmon, in the net pen. In addition to the treatments registered directly according to the protocol, we retrieved data for additional treatments directly from the aquaculture companies' own registration system. The objectives of this observational study was (1) investigate whether salmon lice detach during crowding before an NMM; (2) investigate the effect of NMM; and (3) investigate possible re-attachment after delousing. We observed an overall trend of a reduction of salmon lice numbers, with a median percentage decrease of 22% for PA/AM and 29% for adult female lice during crowding. A likely explanation for these observations is that lice detach from the salmon due to mechanical action associated with the increased density of crowding. One-sided Wilcoxon tests corroborated the hypothesis of a reduction in lice counts during crowding for PA/AM and adult female lice (p < 0.05). As expected, we also observed a substantial reduction in lice numbers from Sample 1 to Sample 2, which is most likely due to the effect of the delousing treatment with the NMM. We observed an increase in sessile and PA/AM salmon lice when studying possible re-attachment after delousing. For sessile lice, the increase in lice numbers was most likely due to new infestation. For PA/AM, the increase can primarily be explained by re-infestation with lice that detached during crowding. The increase for PA/AM was greater when the salmon were placed in the same cage (a doubling of lice numbers), compared to placing them in a new cage (p < 0.05), indicating that the salmon lice could re-infest to a greater extent when the salmon were moved a shorter distance. The results presented in this article shed light on the possible dispersal of parasitic salmon lice, which is largely an unexplored topic.

Reduced Infestation Levels of Lepeophtheirus salmonis in Atlantic Salmon (Salmo salar) following Immersion Exposure to Probiotic Aliivibrio spp.

Salmon lice (Lepeophtheirus salmonis) constitute a major challenge during the production of farmed Atlantic salmon in Norway. Preventive measures are considered to have a higher impact on sustainable control than lice treatment. Therefore, the studies presented here aimed to document the preventive effects of probiotic Aliivibrio spp. on lice infestation in experimental challenges. A reduction in salmon lice attachment success (58–65%) was observed in two separate aquarium trials, where Atlantic salmon were exposed to different compositions of Aliivibrio species 91 and 155 days prior to lice challenge. In a third trial, no difference in attachment was observed in groups exposed to probiotics 58 days prior to lice challenge compared to controls. However, a relative reduction in lice counts was seen on movable stages later in the trial. High levels of probiotic bacteria had no impact on lice viability in an in vitro bioassay on the preadult life stage; thus, the mechanism behind the preventative effect remains unknown. In conclusion, probiotic Aliivibrio bacteria can likely be used as a preventive tool to reduce salmon louse infestations in the salmon industry. The mechanism is still unknown, and this novel approach to lice control warrants further investigation to understand its optimal use and potential.

The digestion time for salmon louse (Lepeophtheirus salmonis) in lumpfish (Cyclopterus lumpus)

Atlantic salmon aquaculture employs lumpfish as a control method to combat ectoparasites, given their unique cleaning behaviour. There are multiple studies which estimate the average number of salmon lice in the stomach contents of dissected lumpfish. However, these numbers cannot be used to assess the cleaning efficacy of lumpfish (e.g., the average number of lice consumed daily per lumpfish) without knowing the digestion time of lice in lumpfish. The aim of the study was to provide quantitative estimates of the degradation of salmon lice, through a blinded clinical study over a duration of seven days. Individually tagged lumpfish (45.8 g, SD ± 10.28) were randomly arranged in triplicate tanks (n = 28 per tank) and acclimatised for three days. Subsequently, lumpfish were fed using oral gavage dosing with counts of lice (0–6), feed pellets (0–6) or a combination of both. Lice used were recently captured and stored at −80 °C to prevent parasite transmission at the study location and photographed before and after digestion to estimate degradation. Samplings ranged from 6 h intervals during the first two days, to 24 h and eventually 48 h for the last two days. Analysis of salmon lice revealed an expected digestion time of 29 h while the median digestion time was estimated to 15 h at 9 °C. Pellets dissolved quickly and had no impact on the lice digestion time. The findings of this study can be used to estimate cleaning efficacy of lumpfish from stomach contents of salmon lice.

Epidemiology and therapeutic efficacy of a synthetic pyrethroid against Haematopinus tuberculatus (Phthiraptera: Haematopinidae) in Bubalus bubalis

Lice (Insecta: Pthiraptera) are common ectoparasite of buffalos (Bubalis bubalis) causing huge economic loss. An epidemiological survey was conducted in selected tehsils (administrative division) of Faisalabad district to determine the prevalence of lice infestation and the efficacy of cypermethrin (CYP) against lice infestation in buffalos. To determine the efficacy of CYP, 40 lice-infested buffaloes were divided into two groups i.e. drug-treated group and control group (each group contains 20 animals). Cypermethrin drug was used as pour-on at day 0 and lice counts were conducted on days 0, 7, 21, 35, 49, and 63 from predilection sites of each animal. Only one species of sucking louse Haematopinus tuberculatus was found in buffalo population of Faisalabad district. The overall prevalence of lice infestation was 37.76%. The variable like age and sex showed significant (P&lt;0.05) variation of lice infestation while breed showed insignificant variation. Among extrinsic factors, seasons, floor pattern, and feeding system showed significant association (P&lt;0.05) with lice infestation, while animal keeping as free or tethered and tehsils showed an insignificant association. On day 7, 100% effective results were obtained while 99.6% at day 21 and 100% from day 35 till day 63. No clinical adverse reaction was observed during this trial and cypermethrin was found efficacious. Based on these results it can be concluded that cypermethrin is an effective drug against lice infestation.

Discomfort Behaviour and Hair Coat Density of Muurah × Nili-Ravi Cross-bred Buffaloes as Affected by Louse (Haematopinus tuberculatus) Treated with Acaricides

Buffalo farming is an important component of Sri Lankan dairy industry. Ecto-parasites live on the surface of epidermis cause irritation and associated discomfort behaviours leading to energy loss and finally affect to reduce the performance of buffaloes. Objective of the study was to investigate the significance of Louse (Haematopinus tuberculatus) infestation on discomfort behavior and hair coat density of Muurah × Nili-Ravi cross-bred buffaloes reared under semi-intensive farming in Kamburupitiya area in Southern Province in Sri Lanka. Lactating female buffaloes (n=5) represented from parity 1 to 5 were purposively selected to the study. Lice count (LC) and lice egg count (LEC) per unit body area and the hair coat density (HCD) were measured periodically at 5,10,15,20 and 25 days after application of acaricides. Six random samples were taken. Direct focal observations were made to understand the discomfort behaviors (scratching, rubbing, licking, tail wagging and ear wagging) using an ethogram. Variation of LC after treatment was tested using repeated measure ANOVA. Main effects and interaction effects were tested. Correlations between LC and LEC with the HCD were tested. A strong positive correlation (r=0.909) was observed between LEC and the HCD whereas a weak positive correlation (r=0.439) was observed between LC and the HCD. With the prolongation of treatment time, the LC was increased and from day 15 to 25 it was significantly (p&lt;0.05) increased. With the age advancement, the HCD was decreased. All the discomfort behaviors were significantly (p&lt;0.05) increased with the prolongation of days after acaricide treatments. It is concluded that irrespective of the age, with the increased duration after applying acaricide treatment, lice infestation also simultaneously increased causing discomfort to the animals. Application of acaricides again at 15 days is recommended to control lice and to free the buffaloes from discomfort.&#x0D; Keywords: Acaricides, Buffalo, Discomfort behaviors, Hair coat density, Lice infestation

Salmon lice in the Pacific Ocean show evidence of evolved resistance to parasiticide treatment

Parasitic salmon lice (Lepeophtheirus salmonis) threaten the economic and ecological sustainability of salmon farming, and their evolved resistance to treatment with emamectin benzoate (EMB) has been a major problem for salmon farming in the Atlantic Ocean. In contrast, the Pacific Ocean, where wild salmon are far more abundant, has not seen widespread evolution of EMB-resistant lice. Here, we use EMB bioassays and counts of lice on farms from the Broughton Archipelago, Canada—a core region of salmon farming in the Pacific—to show that EMB sensitivity has dramatically decreased since 2010, concurrent with marked decrease in the field efficacy of EMB treatments. Notably, these bioassay data were not made available through public reporting by industry or by the federal regulator, but rather through Indigenous-led agreements that created a legal obligation for salmon-farming companies to provide data to First Nations. Our results suggest that salmon lice in the Pacific Ocean have recently evolved substantial resistance to EMB, and that salmon-louse outbreaks on Pacific farms will therefore be more difficult to control in the coming years.

System-specific salmon louse infestation thresholds for salmon farms to minimize impacts on wild sea trout populations

Salmon lice Lepeophtheirus salmonis from aquaculture can cause negative impacts on sea trout Salmo trutta and other wild salmonids. Long-term records from 5 Irish rivers were used to explore relationships between annual sea trout runs and estimated total number of lice on nearby salmon farms. It was hypothesised that local environmental conditions may result in system-specific differences in realised louse pressure on sea trout. Louse count was thus tested as an absolute number and as a relative pressure, i.e. standardised by farm. When the standardised total number of mobile lice on a given salmon farm in April was above baseline level (50th percentile of observed annual values on that farm), there was a high probability of a below-average sea trout run in the local river. Absolute louse counts did not show an important effect on runs. This finding suggests that salmon farm louse production in spring can have a strong system-specific regulating effect on wild sea trout populations. Total number of lice on a farm was most strongly driven by changes in individual infestation rate, with a lesser effect of stocking density. Thresholds for number of mobile lice per farmed salmon required to maintain total louse count below the baseline varied with stocking density and among systems: greater density required lower infestation rate. Regulations relying on a generic louse threshold to trigger treatment are not sufficient to protect sea trout populations—stocking density and site characteristics must be considered to evaluate system-specific infestation pressure and impacts on wild salmonids.

Sea-louse abundance on salmon farms in relation to parasite-control policy and climate change

Abstract The ectoparasitic copepods, sea lice (Lepeophtheirus salmonis and Caligus spp.), are major pests to salmon aquaculture and can also affect the health and survival of wild salmon. Policies exist to protect wild salmon by delousing farmed fish when louse abundance exceeds a threshold, but their effectiveness under future climate change is uncertain. We fitted a Bayesian model for sea-louse population dynamics and management to timeseries data of sea lice on farmed salmon in Pacific Canada and analysed the model under scenarios of warmer climates. We found that in high-temperature years, current parasite control policy becomes ineffective as sea-louse abundance is expected to increase. We simulated two alternative management scenarios and observed that both would decrease average louse counts on farms in high-temperature years relative to the current system but relied on more delousing treatments than are currently performed. We also found evidence that non-salmonids can play a role in louse transmission to farms, as increased farm colonization of Caligus clemensi occurs in April, coincident with wild herring (Clupea pallasii) spawner abundance. Our results highlight the need for careful management of sea lice on salmon farms in warmer years and the importance of policies designed to account for future environmental change.

Desempenho, qualidade de ovos e controle de ectoparasitas em poedeiras em idades avançadas suplementadas com produto homeopático

Produtos homeopáticos são uma das principais alternativas aos alopáticos, tendo diversos produtos comerciais para uso veterinário disponíveis no mercado para diferentes finalidades. Por isso, objetivou-se avaliar o desempenho zootécnico, qualidade de ovos e a contagem de ectoparasitas (piolhos) em poedeiras com idades avançadas. O experimento foi realizado no Instituto Federal do Triângulo Mineiro - campus Uberaba, utilizando 90 aves da linhagem comercial Delkalb®, com idade de 89 a 93 semanas, distribuídas em delineamento inteiramente casualizado, divididas em três tratamentos com cinco repetições contendo 6 aves por repetição totalizando 30 aves por tratamento. Os tratamentos utilizados consistiram em: tratamento 1 – sem uso do produto homeopático; tratamento 2 – 1,0 g/ave/dia do aditivo homeopático, tratamento 3 – 1,5 g/ave/dia do aditivo homeopático. Não foi observada diferença estatísticas sobre o desempenho zootécnico e qualidade de ovos, contudo a percentual de postura das aves estavam em valores esperados para a idade das aves, já sobre a qualidade de ovos pode ser observado que a unidade Haugh ficou muito abaixo dos valores encontrados na literatura. A contagens de ectoparasitas não foi estatisticamente influenciado pela utilização do produto homeopático, este efeito pode ser explicado devido ao alto índice de infestação de piolhos que acometeram sobre as aves. Conclui-se que o produto homeopático utilizado não foi eficiente no controle da infestação de ectoparasitas (piolhos) presente nas aves, contudo o mesmo não proporcionou efeitos adversos sobre, desempenho zootécnico ou qualidade de ovos.

Effect of cleaner fish on sea lice in Norwegian salmon aquaculture: a national scale data analysis

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.

Parasitic sea louse infestations on wild sea trout: separating the roles of fish farms and temperature

BackgroundThe causal relation between parasitic sea lice on fish farms and sea lice on wild fish is a controversial subject. A specific scientific debate has been whether the statistical association between infestation pressure (IP) from fish farms and the number of parasites observed on wild sea trout emerges purely because of a confounding and direct effect of temperature (T).MethodsWe studied the associations between louse infestation on wild sea trout, fish farm activity and temperature in an area that practices coordinated fallowing in Nordhordland, Norway. The data were sampled between 2009 and 2016. We used negative binomial models and mediation analysis to determine to what degree the effect of T is mediated through the IP from fish farms.ResultsThe number of attached lice on sea trout increased with the T when the IP from fish farms was high but not when the IP was low. In addition, nearly all of the effect of rising T was indirect and mediated through the IP. Attached lice remained low when neighbouring farms were in the first year of the production cycle but rose substantially during the second year. In contrast to attached lice, mobile lice were generally seen in higher numbers at lower water temperatures. Temperature had an indirect positive effect on mobile louse counts by increasing the IP which, in turn, raised the sea trout louse counts. Mobile louse counts rose steadily during the year when neighbouring farms were in the first year of the production cycle and stayed high throughout the second year.ConclusionsThe estimates of the IP effect on louse counts along with the clear biennial pattern emerging due to the production cycle of fish farms clearly indicate that fish farms play an important role in the epidemiology of sea lice on wild sea trout. Furthermore, the mediation analysis demonstrates that a large proportion of the effect of T on louse counts is mediated through IP.

Tool for predicting Caligus rogercresseyi abundance on salt water salmon farms in Chile

Caligus rogercresseyi is a host-dependent parasite that affects rainbow trout and Atlantic salmon in Chile. Numbers of sea lice on fish increase over time at relatively predictable rates when the environment is conducive to the parasite’s survival and fish are not undergoing treatment. We developed a tool for the salmon industry in Chile that predicts the abundance of adult sea lice over time on farms that are relatively isolated.We used data on sea louse abundance collected through the SalmonChile INTESAL sea lice monitoring program to create series of weekly lice counts between lice treatment events on isolated farms. We defined isolated farms as those with no known neighbors within a 10 km seaway distance and no more than two neighbors within a 20 km seaway distance. We defined the time between sea lice treatments as starting the week immediately post treatment and ending the week before a subsequent treatment. Our final dataset of isolated farms consisted of 65 series from 32 farms, between 2009 and 2015.Given an observed abundance at time t = 0, we built a model that predicted 8 consecutive weekly sea louse abundance levels, based on the preceding week’s lice prediction. We calibrated the parameters in our model on a randomly selected subset of training data, choosing the parameter combinations that minimized the absolute difference between the predicted and observed sea louse abundance values.We validated the parameters on the remaining, unseen, subset of data. We encoded our model and made it available as a Web-accessible applet for producers.We determined a threshold, based on the upper 97.5% predictive interval, as a guideline for producers using the tool. We hypothesize that if farms exceed this threshold, especially if the sea lice levels are above this threshold 2 and 4 weeks into the model predictions, the sea louse population on the farm is likely influenced by sources other than lice within the farm.

Reduced exposure of farmed salmon to salmon louse (Lepeophtheirus salmonis L.) infestation by use of plankton nets: Estimating the shielding effect

Salmon louse infestation is arguably the most limiting factor for further growth in the production of farmed salmon in Norway. Since the use of pesticides has become less effective in controlling infestations due to evolving resistance in the salmon louse, the development of novel non-medical control methods is in focus. A variety of new methods are being launched, but limited effort is spent on documenting control effects. Here we present an analysis that quantifies the effect of shielding farmed salmon from exposure to infestive salmon lice by using plankton nets surrounding the upper parts of cages. The temporal development of salmon louse infestations was compared for production cages shielded with 10 m and/or 6 m deep plankton nets, or no nets (controls), in five full scale salmon farms. Only weeks where lice counts were available from both control cages and plankton net shielded cages were included in the data. Varying external and internal infestation pressure exposing the test farms was controlled for in the analysis by quantifying the reproduction of infestive lice from external farms and from the test farm. We found that use of plankton nets significantly reduced the rate of new salmon louse infestation. The shielding effect amounted to an estimated 30% weekly reduction (95% CI: 18–41%) in the rate of new infestations of pre-adult and adult male lice (PAAM) one week ahead in large scale production cages. We conclude that the use of plankton nets represents a non-medical complementary method in the pest management of salmon lice that may reduce the need for treatments, either with pesticides or other non-medical measures, and further contribute to conserve effects of pesticides used to control salmon lice infestations in salmon farming.

Essential oils in the management of the donkey louse, Bovicola ocellatus.

Chewing lice are widespread and clinically compromising parasites of livestock and equids. Their management is complicated by growing levels of resistance to commonly applied insecticides. Hence, the development of novel approaches to their control is of major clinical interest. To assess the effects of incorporating the essential oils of tea tree and lavender into a grooming programme for populations of donkeys with natural infestations of Bovicola ocellatus in the UK and Ireland when louse populations were at their winter seasonal peak. In vivo field trial. Suspensions of 5% (v/v) tea tree or lavender oil or an excipient only control were groomed into the coats of winter-housed donkeys (n = 198) on 2 occasions, 2 weeks apart. Louse counts were conducted before each application and 2 weeks later. After 2 applications, the groups groomed with lavender or tea tree oil suspensions had a significant reduction in louse intensity, with a mean decline in louse abundance of 78% (95% confidence interval 76-80%). Louse numbers in the groups groomed with excipient only either did not change or increased significantly. Donkey hair length had no effect on the decline in louse numbers. These results demonstrate that the inclusion of essential oil suspensions during grooming can be used to manage louse populations successfully.

Effect of pour-on alphacypermethrin on feed intake, body condition score, milk yield, pregnancy rates, and calving-to-conception interval in buffaloes.

The aims of this study were to assess the efficacy of alphacypermethrin (ACYP) on pediculosis due to Haematopinus tuberculatus and to evaluate the influence of the treatment on productive and reproductive performance in buffaloes (Bubalus bubalis) reared in an intensive system. The trial was performed on 56 pluriparous buffaloes at 86.8 ± 8.1 d in milk. The animals underwent individual louse count and were divided into 2 homogenous groups according to louse count, age, number of lactations, days in milk, live BW, BCS, pregnancy status, and milk yield. Group A (n = 28) was treated by a pour-on formulation of ACYP, and Group S (n = 28) was treated by pour-on saline solution. Individual louse counts were performed weekly on 10 buffaloes in each group. Feed intake was recorded daily and the total mixed ration, individual ingredients, and orts were analyzed to calculate DM ingestion. Individual milk yield was recorded daily and milk samples were analyzed at the beginning of the trial, after 4 wk, and at the end of the trial to assess milk composition. Individual BCS was also evaluated simultaneously. Finally, the animals underwent synchronization of ovulation starting 4 wk after treatment and the pregnancy rate and the calving-conception interval were evaluated. Data were analyzed by the Mann-Whitney test and ANOVA for repeated measures. The infestation was constant in Group S, whereas no lice were present in Group A throughout the study. Daily DMI was similar in the 2 groups (16.7 ± 0.4 vs. 16.3 ± 0.3 kg/d in Group A vs. Group S, respectively), although buffaloes in Group A showed higher (P < 0.05) BCS score at the end of the trial (7.39 ± 0.1 vs. 7.14 ± 0.1 in Group A vs. Group S, respectively). The average milk yield/buffalo was higher (P < 0.05) in Group A compared to Group S (10.58 ± 0.1 vs. 10.39 ± 0.1 kg in Group A vs. Group S, respectively) and this was mainly due to the higher milk production recorded in buffaloes at less than 75 d in milk (11.81 ± 0.1 vs. 11.45 ± 0.1 kg in Group A vs. Group S, respectively). Despite of a similar fertility rate (90.5 vs. 80.9% in Group A vs. Group S, respectively), a lower (P < 0.05) calving-conception interval was recorded in Group A compared to Group S (118 ± 16 vs. 177 ± 16 d in Group A vs. Group S, respectively). In addition to the pour-on treatment against pediculosis, productive and reproductive performance were also improved. This represents a significant improvement in dairy buffalo herd management.

Difference in skin immune responses to infection with salmon louse (Lepeophtheirus salmonis) in Atlantic salmon (Salmo salar L.) of families selected for resistance and susceptibility

Atlantic salmon is susceptible to the salmon louse (Lepeophtheirus salmonis) and the variation in susceptibility within the species can be exploited in selective breeding programs for louse resistant fish. In this study, lice counts were completed on 3000 siblings from 150 families of Atlantic salmon identified as high resistant (HR) and low resistant (LR) families in two independent challenge trials. Skin samples behind the dorsal fin (nearby lice attachment) were collected from ten extreme families (HR or LR) and analyzed by qPCR for the expression of 32 selected genes, including a number of genes involved in T helper cell (Th) mediated immune responses, which have been previously implied to play important roles during salmon louse infections.Most genes showed lower expression patterns in the LR than in HR fish, suggesting an immunosuppressed state in LR families. The average number of lice (chalimi) was 9 in HR and 15 in LR fish. Large variation in lice counts was seen both within resistant and susceptible families, which enabled us to subdivide the groups into HR < 10 and HR > 10, and LR < 10 and LR > 10 to better understand the effect of lice burden per se. As expected, expression patterns were influenced both by genetic background and the number of attached parasites. Higher number of lice (>10) negatively affected gene expression in both HR and LR families. In general, strongest down-regulation was seen in LR > 10 and lesser down-regulation in HR < 10. HR in general and especially HR < 10 fish were better at resisting suppression of expression of both Th1 and Th2 genes. However, the best inverse correlation with infection level was seen for the prototypical Th1 genes, including several members from the interferon pathways. In addition, skin histomorphometry suggests that infected LR salmon had thicker epidermis in the area behind the dorsal fin and larger mucous cell size compared to infected HR fish, however marginally significant (p = 0.08). This histomorphometric finding was in line with the immune response being skewed in LR towards the Th2 rather than a Th1 profile. Our findings suggest that the ability to resist lice infection depends on the ability to avoid immunosuppression and not as much on the physical tissue barrier functions.

First report of winter epizootic of salmon lice on sea trout in Norway

Here we report on the first observation of a winter epizootic of salmon lice Lepeoph- theirus salmonis Kroyer on sea trout Salmo trutta Linnaeus in a Norwegian fjord with intensive salmon farming. Trouts were sampled and counts of lice in the field were made for 2 consecutive winter seasons with trap nets in 2013 and 2014 just inside and outside the border to the National Salmon Fjord in Sognefjorden, western Norway. The aim of the study was to document potential epizootic outbreaks during the winter months. Following reports and field registrations of high abundance of lice in February and early March 2014, 12 and 14 fish were sampled from the 2 loca- tions between 9 and 24 March and analyzed in the laboratory. Prevalence of sea lice on sampled fish inside and outside the fjord was 100 and 74%, with a mean abundance of 254.3 and 26.8 and a mean average intensity of 254.3 (max = 759) and 37.5 (max = 188), respectively. Chalimus stages dominated on the fish. In comparison, prevalence and abundance based on field observations in 2013 were low and dominated by adult stages. We suggest that the winter epizootic observed in 2014 and not in 2013 may be a result of the combined effect of production of salmon lice in nearby fish farms and the prevailing environmental conditions.

The efficacy and safety of alphacypermethrin as a pour-on treatment for water buffalo (Bubalus bubalis) infested with Haematopinus tuberculatus (Phthiraptera: Haematopinidae)

The sucking louse Haematopinus tuberculatus (Burmeister 1839) is an ectoparasite of buffaloes, cattle, camels, and American bison. Alphacypermethrin (ACYP) is a pyrethroid insecticide commonly used to control arthropods of veterinary and public health interest. Therapeutics, such as antiparasitic compounds, is often administered to buffaloes based on dosage and intervals recommended for cattle because very few drugs have buffalo-specific label indications. A trial was conducted on 20 louse-infested buffaloes at a farm to assess the efficacy and safety of ACYP pour-on, at the manufacturer's recommended dose for cattle, on buffaloes naturally infested by H. tuberculatus. Ten animals were assigned to ACYP-treated group (ACYP-group) and ten to untreated control group (C-group). On day 0, all ACYP-group buffaloes received alphacypermethrin pour-on. Louse counts were performed on days -1, 7, 14, 21, 28, 35, 42, 49, and 56 at eight predilection sites on the skin of each buffalo. ACYP was completely effective (100%) at day 7, highly effective (99.8%) at day 14, and completely effective (100%) from day 21 until the end of the study (day 56 post-treatment). During the trial, ACYP was well tolerated by all animals as there were no observed clinically adverse reactions. The results of this trial suggest that ACYP is an effective, safe, and user-friendly compound suitable for treatment of buffaloes with natural louse infestations.

Field efficacy of eprinomectin against the sucking louse Haematopinus asini on naturally infested donkeys

A trial was conducted to assess the efficacy of eprinomectin (EPR) against the sucking louse Haematopinus asini on naturally infested donkeys. Parasitological investigations were performed on fifteen animals. On day 0, donkeys received EPR pour-on at the manufacturer’s recommended cattle dose. Louse counts were performed on days −1, 7, 14, 21, 28, 35, 42, 49 and 56 at seven predilection sites on the skin of each donkey. EPR was completely effective (100%) from day 7, until the end of the study. Clinically no adverse reactions were observed in any of donkeys treated. EPR was considered to be 100% effective against H. asini. This is the first trial to evaluate the efficacy of EPR against a natural louse infestation in donkeys.

Modeling Parasite Dynamics on Farmed Salmon for Precautionary Conservation Management of Wild Salmon

Conservation management of wild fish may include fish health management in sympatric populations of domesticated fish in aquaculture. We developed a mathematical model for the population dynamics of parasitic sea lice (Lepeophtheirus salmonis) on domesticated populations of Atlantic salmon (Salmo salar) in the Broughton Archipelago region of British Columbia. The model was fit to a seven-year dataset of monthly sea louse counts on farms in the area to estimate population growth rates in relation to abiotic factors (temperature and salinity), local host density (measured as cohort surface area), and the use of a parasiticide, emamectin benzoate, on farms. We then used the model to evaluate management scenarios in relation to policy guidelines that seek to keep motile louse abundance below an average three per farmed salmon during the March–June juvenile wild Pacific salmon (Oncorhynchus spp.) migration. Abiotic factors mediated the duration of effectiveness of parasiticide treatments, and results suggest treatment of farmed salmon conducted in January or early February minimized average louse abundance per farmed salmon during the juvenile wild salmon migration. Adapting the management of parasites on farmed salmon according to migrations of wild salmon may therefore provide a precautionary approach to conserving wild salmon populations in salmon farming regions.