A 2-stage hierarchical interrupted time-series analysis to quantify the long-term effect of subclinical bacterial kidney disease on performance of farmed Atlantic salmon (Salmo salar L.).

Bacterial Kidney Disease (BKD) is an economically significant disease in salmonid aquaculture and commonly requires antibiotic treatments to reduce its impact. Once a pen of fish is diagnosed with BKD, fish are considered chronically infected, potentially until harvest. Although there appears to be little or no evidence to support it, it is often assumed that subclinical infections affect productivity over the long term. We used a 2-stage hierarchical interrupted time series (ITS) analysis in an attempt to quantify the effect of subclinical BKD on mortality, growth, and food conversion ratio (FCR) of Atlantic salmon cultured in marine farms in Atlantic Canada. For all three outcomes, BKD had for some site cycles a positive effect, and for others a negative effect. Overall, the effect of BKD on mortality and growth could not be detected (effect -0.08 ((95% ci: -0.51, 0.35) and 0.00 (-0.02, 0.02)), while a very small effect showing an increase in FCR was detected (0.07 (-0.01, 0.15)). We hypothesized that minimal interference with fish performance may be compatible with the ecology of Renibacterium salmoninarum, the causative agent of BKD. For this organism, vertical transmission is a primary mode of propagation in low-density host populations as found in the wild. Since farms are always adapting and optimizing their farm management of BKD, these constant adjustments may also have negated our ability to detect the effect of many factors contributing to BKD productivity impacts. Hierarchical ITS analysis is considered an appropriate methodology to investigate the complex relationships with productivity measures over time under farming conditions. In the highly innovative salmon aquaculture industry, health records generating data available for time-series analysis is expected to become more accurate and abundant in the future, providing more opportunities for time-series regression studies.

Risk factors associated with time to first clinical case of Bacterial Kidney Disease (BKD) in farmed Atlantic Salmon (Salmo salar L.) in New Brunswick, Canada.

Infection with Renibacterium salmoninarum, the cause of Bacterial Kidney Disease (BKD) occurs in salmon populations in many locations, including the east coast of Canada. However, information about risk factors for BKD and their effects in the saltwater phase of the salmon aquaculture industry in the region is inadequate. We conducted a retrospective observational cohort study using industry health records in which BKD was recorded in New Brunswick, Canada, between 2006 and 2012. Several risk factors for BKD, such as stocking season, mortality percentage in the first four weeks, food conversion ratio (FCR), lice treatment, Bay Management Area (BMA), and production year were analyzed in a survival analysis using Cox proportional hazards models with cross-classified random effects to account for the structure of the data. The models incorporated effects on two different time scales, time since stocking and calendar time. The risk period was from stocking in salt water to first occurrence of clinical BKD in a pen. Results were time varying. Stocking season had a pronounced effect on time to clinical BKD after middle October of the first year after stocking, with clinical cases occurring less frequently in fall/winter-stocked fish compared to summer and spring-stocked fish; for example, in middle October, the Hazard Ratio of spring- compared to fall/winter-stocked fish was 15.8 (95% CI; 1.05, 354). Differences lasted until June and July of the second year after stocking. Effects of final hatchery before transfer to seawater, and egg source were not detected, but a limitation of this study was that this information was not available for 44.3% of the fish groups in our dataset. BKD status of a site/pen before fallow period and distance to nearest site with BKD were also not detected. Feed conversion ratio and mortality during the first four weeks affected BKD, indicating that better performing fish have a reduced hazard for BKD or vice versa, and implying that good general husbandry practices and BKD are correlated.

Evaluating bath treatment effectiveness in the control of sea lice burdens on Atlantic salmon in New Brunswick, Canada.

The use of medicinal bath treatment for sea lice is becoming more common, due to increasing resistance to in-feed treatments with emamectin benzoate. Common treatment modalities in New Brunswick, Canada, include Salmosan administered by tarpaulin or wellboat, and Paramove administered by wellboat. In this study, we assessed the effectiveness of these treatment modalities in the field between 2010 and 2015 using a web-based sea lice data management system (Fish-iTrends© ). Effectiveness was evaluated for adult female (AF) and for pre-adult and adult male (PAAM) life stages separately. We also investigated the impact of variability in pretreatment lead and post-treatment lag time on effectiveness measures. There were 1185 treatment events at 57 farms that uniquely matched our pre- and post-treatment count criteria. The effectiveness of treatment modality was significantly influenced by season, pretreatment level of sea lice and by lead and lag times. In summer, Salmosan administered by tarpaulin had the greatest effectiveness on both AF and PAAM, when pretreatment levels were above 10 sea lice; whereas in autumn, the performance of treatment modalities varied significantly, depending on the pretreatment levels for the life stages. Ignoring the lead or lag time effect generally resulted in an underestimation of treatment effectiveness.

Effect of timing of count events on estimates of sea lice abundance and interpretation of effectiveness following bath treatments.

Effectiveness of sea lice bath treatment is often assessed by comparing pre- and post-treatment counts. However, in practice, the post-treatment counting window varies from the day of treatment to several days after treatment. In this study, we assess the effect of post-treatment lag time on sea lice abundance estimates after chemical bath treatment using data from the sea lice data management program (Fish-iTrends) between 2010 and 2014. Data on two life stages, (i) adult female (AF) and (ii) pre-adult and adult male (PAAM), were aggregated at the cage level and log-transformed. Average sea lice counts by post-treatment lag time were computed for AF and PAAM and compared relative to treatment day, using linear mixed models. There were 720 observations (treatment events) that uniquely matched pre- and post-treatment counts from 53 farms. Lag time had a significant effect on the estimated sea lice abundance, which was influenced by season and pre-treatment sea lice levels. During summer, sea lice were at a minimum when counted 1 day post-treatment irrespective of pre-treatment sea lice levels, whereas in the spring and autumn, low levels were observed for PAAM over a longer interval of time, provided the pre-treatment sea lice levels were >5-10.

Case definition for clinical and subclinical bacterial kidney disease (BKD) in Atlantic Salmon (Salmo salar L.) in New Brunswick, Canada.

Bacterial kidney disease (BKD) is considered an important cause of loss in salmon aquaculture in Atlantic Canada. Causative agent of BKD is the Gram-positive bacteria Renibacterium salmoninarum. Infected salmon are often asymptomatic (subclinical infection), and the disease is considered chronic. One of the challenges in quantifying information from farm production and health records is the application of a standardized case definition. Case definitions for farm-level and cage-level clinical and subclinical BKD were developed using retrospective longitudinal data from aquaculture practices in New Brunswick, Canada, combining (i) industry records of weekly production data including mortalities, (ii) field observations for BKD using reports of veterinarians and/or fish health technicians, (iii) diagnostic submissions and test results and (iv) treatments used to control BKD. Case definitions were evaluated using veterinarians' expert judgements as reference standard. Eighty-nine and 66% of sites and fish groups, respectively, were associated with BKD at least once. For BKD present (subclinical or clinical), sensitivity and specificity of the case definition were 75-100% varying between event, fish group, site cycle and level (site pen). For clinical BKD, sensitivities were 29-64% and specificities 91-100%. Industry data can be used to develop sensitive case definitions.

Variation in pre-treatment count lead time and its effect on baseline estimates of cage-level sea lice abundance.

Treatment efficacy studies typically use pre-treatment sea lice abundance as the baseline. However, the pre-treatment counting window often varies from the day of treatment to several days before treatment. We assessed the effect of lead time on baseline estimates, using historical data (2010-14) from a sea lice data management programme (Fish-iTrends). Data were aggregated at the cage level for three life stages: (i) chalimus, (ii) pre-adult and adult male and (iii) adult female. Sea lice counts were log-transformed, and mean counts by lead time relative to treatment day were computed and compared separately for each life stage, using linear mixed models. There were 1,658 observations (treatment events) from 56 sites in 5 Bay Management Areas. Our study showed that lead time had a significant effect on the estimated sea lice abundance, which was moderated by season. During the late summer and autumn periods, counting on the day of treatment gave significantly higher values than other days and would be a more appropriate baseline estimate, while during spring and early summer abundance estimates were comparable among counts within 5 days of treatment. A season-based lead time window may be most appropriate when estimating baseline sea lice levels.

A fixed-dose approach to conducting emamectin benzoate tolerance assessments on field-collected sea lice, Lepeophtheirus salmonis.

In New Brunswick, Canada, the sea louse, Lepeophtheirus salmonis, poses an on-going management challenge to the health and productivity of commercially cultured Atlantic salmon, Salmo salar. While the in-feed medication, emamectin benzoate (SLICE® ; Merck), has been highly effective for many years, evidence of increased tolerance has been observed in the field since late 2008. Although bioassays on motile stages are a common tool to monitor sea lice sensitivity to emamectin benzoate in field-collected sea lice, they require the collection of large numbers of sea lice due to inherent natural variability in the gender and stage response to chemotherapeutants. In addition, sensitive instruments such as EC(50) analysis may be unnecessarily complex to characterize susceptibility subsequent to a significant observed decline in efficacy. This study proposes an adaptation of the traditional, dose-response format bioassay to a fixed-dose method. Analysis of 657 bioassays on preadult and adult stages of sea lice over the period 2008-2011 indicated a population of sea lice in New Brunswick with varying degrees of susceptibility to emamectin benzoate. A seasonal and spatial effect was observed in the robustness of genders and stages of sea lice, which suggest that mixing different genders and stages of lice within a single bioassay may result in pertinent information being overlooked. Poor survival of adult female lice in bioassays, particularly during May/June, indicates it may be prudent to consider excluding this stage from bioassays conducted at certain times of the year. This work demonstrates that fixed-dose bioassays can be a valuable technique in detecting reduced sensitivity in sea lice populations with varying degrees of susceptibility to emamectin benzoate treatments.

Sea lice monitoring on Atlantic salmon farms in New Brunswick, Canada: comparing audit and farm staff counts.

Sea lice audits were performed by the Atlantic Veterinary College on commercial aquaculture sites in New Brunswick, Canada, in 2011. Although the primary objective was to verify that farms were reporting similar lice counts to third-party counts, more detailed comparisons were made to identify when lice counts were more likely to differ between the audit team and farm employees. A total of 28 sea lice audits were conducted on 16 sites between June and December 2011. During each audit, 10 cages were evaluated per site where possible, with ten fish per cage being evaluated by an audit technician and a further ten by a farm employee. Data analysis included descriptive statistics of lice counts by stage and limits of agreement plots. A random effects negative binomial model that accounted for clustering of cages within sites was applied to assess the effect of counter type and season on lice counts by stage. The results indicate that farms counts were generally in agreement with audit counts. However, when the average counts for chalimus and preadult (male and female) and adult male lice stages were high, farm counters were more likely to report a lower value. Higher lice counts were observed during autumn compared to summer especially for the adult female stage. Finally, there was a significant clustering effect for site and cage, with most of the variation attributable to site.

Detection of emamectin benzoate tolerance emergence in different life stages of sea lice, Lepeophtheirus salmonis, on farmed Atlantic salmon, Salmo salar L.

Emamectin benzoate has been used to treat sea lice, Lepeophtheirus salmonis, infestations on farmed Atlantic salmon, Salmo salar. Recent evidence suggests a reduction in effectiveness in some locations. A major challenge in the detection of tolerance emergence can be the typically low proportion of resistant individuals in a population during the early phases. The objectives of this study were to develop a method for determining differences in temporal development of tolerance between sea lice life stages and to explore how these differences might be used to improve the monitoring of treatment effectiveness in a clinical setting. This study examined two data sets based on records of sea lice abundance following emamectin benzoate treatments from the west coast of Scotland (2002-2006) and from New Brunswick, Canada (2004-2008). Life stages were categorized into two groups (adult females and the remaining mobile stages) to examine the trends in mean abundance and treatment effectiveness. Differences in emamectin benzoate effectiveness were found between the two groups by year and location, suggesting that an important part of monitoring drug resistance development in aquatic ectoparasites may be the need to focus on key life stages.

Evaluation of external operculum loop tags to individually identify cage-cultured Atlantic halibut Hippoglossus hippoglossus in commercial research trials.

The growth, survival and tag retention of double-tagged [external FT4 lock-on (FT4) and internal passive integrated transponder (PIT)-tagged] Atlantic halibut Hippoglossus hippoglossus were compared to internal PIT-tagged controls in a randomized trial. The objective was to assess the suitability of these tags for monitoring the performance of individual fish in longitudinal trials under commercial cage-culture conditions in the lower Bay of Fundy, New Brunswick, Canada. The FT4 tags were chosen due to their similarity to tags used by investigators to track H. hippoglossus in the wild. A subset of the population randomly received an external FT4 tag inserted through the operculum and were monitored over a 1105 day period. The specific growth rate of FT4-tagged fish was significantly reduced in the first sea summer with no significant difference observed for the remainder of the trial. The differential growth in the first sea summer created a relative size advantage, permitting controls to increase in size significantly faster than FT4 fish in all subsequent periods. The FT4 tags did not significantly influence survival under normal commercial cage-culture conditions. Results, however, suggest that the survival of FT4-tagged H. hippoglossus may be compromised during stressful handling events. Tag retention of FT4 tags was acceptable with 76% of tags remaining at the end of the 1105 day trial. FT4 tags proved to be an effective method to identify individual H. hippoglossus, with the caveat that they seriously bias productivity measures in commercial research trials.

Randomized clinical field trial of a bacterial kidney disease vaccine in Atlantic salmon, Salmo salar L.

A randomized, blinded clinical trial was performed to assess the relative effectiveness of five commercial and one experimental vaccine in a population of farmed fish experiencing a bacterial kidney disease (BKD) outbreak that occurred in one study cage that was part of a larger clinical field trial. A total of 6000 uniquely identified Atlantic salmon S1 presmolts were randomly assigned to vaccine groups in the hatchery and transferred to a commercial marine aquaculture site. Repeated sampling events to evaluate growth, inherent physical conditions and health status were carried out over the entire production cycle. During the second summer at sea, the study cage developed an outbreak of BKD that lasted approximately 240 days. The effectiveness of the selected vaccines was evaluated using survival analysis methods. The sole vaccine group offering protection for BKD was found to significantly decrease the hazard of dying (hazard ratio, HR = 0.68, P = 0.018) during the outbreak, compared to the industry standard, vaccine group. Additionally, during the outbreak, fish with a shortened operculum had a significantly decreased hazard (HR = 0.38, P = 0.033) compared to those fish with a normal operculum, while fish with jaw deformities had a significantly increased hazard (HR = 2.55, P = 0.001) compared to fish with normal jaw status.

Randomized clinical trial to investigate the effectiveness of teflubenzuron for treating sea lice on Atlantic salmon.

A double-blind, randomized control clinical trial was performed to investigate the effectiveness of teflubenzuron in controlling sea lice Lepeophtheirus salmonis on farmed Atlantic salmon Salmo salar. A total of 40 sea cages from 3 commercial cage sites in Atlantic Canada were used in this Good Clinical Practice (GCP) trial. The teflubenzuron was administered in the feed at a dosage of 10 mg kg(-1) biomass d(-1) for 7 d. Medicated and control cages were matched by site, cage size, and pre-treatment mean lice counts using cages as the unit of concern. Post-treatment lice counts and staging of developmental stages were performed at 1 and 2 wk after the end of treatment. Chalimus stages in medicated cages were significantly lower than in control cages at 1 wk (79% reduction in mean lice counts, p < 0.001), and at 2 wk (53% reduction, p < 0.001). Mobile (pre-adult and adult) stages were also significantly reduced in medicated cages at 1 wk (69% reduction, p < 0.01), and at 2 wk (40% reduction, p < 0.01) post-treatment, respectively. Teflubenzuron was proven effective for reducing lice burdens on salmon despite the low parasite levels experienced during the trial and the recruitment of lice from the untreated cages. The use of cage as the unit of concern was an important design component of this trial.

Historical control clinical trial to assess the effectiveness of teflubenzuron for treating sea lice on Atlantic salmon.

A historical control clinical trial was performed to assess the effectiveness of teflubenzuron in controlling sea lice Lepeoptheirus salmonis burdens on farmed Atlantic salmon Salmo salar over time. The study site comprised 9 sea cages, all of which were treated. The teflubenzuron was administered in the feed, at a dosage of 10 mg kg(-1) biomass d(-1), over a treatment period of 7 d. At 1 wk post-treatment, sea lice chalimus and mobile stages were reduced by 92 and 74% (both p < 0.001), respectively. At 2 wk post-treatment, chalimus stages were reduced by 41% and mobile stages 61% (both p < 0.001) compared to pre-treatment levels. At 3 wk post-treatment, chalimus stages were still 36% (p < 0.001) lower than pre-treatment levels, but mobile stages had increased to above pre-treatment levels. Our results show that the effects of teflubenzuron are limited to a 3 wk duration, but that with appropriate management, farms could benefit from these reduced lice burdens for longer periods.

Mortality patterns in infectious salmon anaemia virus outbreaks in New Brunswick, Canada.

Mortality levels attributed to infectious salmon anaemia viral (ISAV) infections were examined at the net pen and site level in the 1996 smolt year class in three areas of New Brunswick, Canada. The year class in this region was the first known to have potential exposure to ISAV beginning at the time of seawater transfer. There was considerable variability in mortality patterns among net pen groups of fish. Net pen outbreak definitions were based on at least seven high mortality days in which there were at least 100 per 100 000 fish per day or >5% cumulative mortality for the study period. There were 106 net pen outbreaks in a study population consisting of 218 net pens. Although the number of new cases decreased as water temperature decreased, overall mortality levels at the study sites did not decrease noticeably. The median peak daily mortality rate during outbreaks was 492 per 100 000 fish per day, with 10% of cases experiencing >5200 mortalities per 100 000 fish per day. The median duration of outbreaks in net pens for which the fish were not slaughtered during the outbreak was 33 days and the median total loss in those outbreaks was 6600 per 100 000 fish.

Risk factors associated with mortalities attributed to infectious salmon anaemia virus in New Brunswick, Canada.

Outbreaks of unexplained mortalities attributed to infectious salmon anaemia (ISA) were examined in the 1996 year class of Atlantic salmon in three regions of New Brunswick, Canada. A total of 218 net pens at 14 sites deemed to have been exposed to ISA virus (ISAV) were surveyed for mortality records and management, environmental and host characteristics. Based on definitions of mortality patterns, clinical ISA disease outbreaks occurred in 106 net pens. There were eight sites in which >50% of net pens experienced ISA outbreaks during the study period. Factors related to their potential role in transmission of virus to new sites or new net pens at the same site were identified as sea lice vectors, divers visiting multiple sites, sites belonging to companies with more than one site, exposure to other year classes at the site, and proximity to other infected net pens. Host resistance factors associated with greater risk of outbreaks were identified as larger groupings, general health following smolt transfer, stressful husbandry procedures during growout, and health or productivity during colder water periods. Despite very close proximity between sites, modification of these management factors would probably influence the severity of mortalities caused by ISAV.

Assessment of infectious salmon anaemia virus prevalence for different groups of farmed Atlantic salmon, Salmo salar L., in New Brunswick.

Abstract Infectious salmon anaemia (ISA) virus (ISAV) has been causing disease in New Brunswick since 1996. As a control measure, all fish in an outbreak cage are killed. The objective of this study was to compare ISAV prevalence in cages experiencing an outbreak with healthy cages from the same farm, neighbouring farms and distant farms. Atlantic salmon from five different groups were tested using an RT-PCR test. Groups included moribund fish from a cage experiencing an outbreak (A), healthy fish from an outbreak cage (B), healthy fish from a negative cage from a farm experiencing an outbreak in a different cage (C), healthy fish from a negative farm near an outbreak farm (D), and healthy fish sampled at a negative farm located in an area with only negative farms (E). Apparent prevalences (standard error) for the different groups (A-E) were 0.94 (+/-0.026), 0.41 (+/-0.062), 0.29 (+/-0.040), 0.08 (+/-0.037) and 0.08 (+/-0.037), respectively. All groups were significantly different (P < 0.002) from each other except for groups B and C and groups D and E. Because the prevalence of the virus was significantly higher in the outbreak cage (B) compared with other sites, early harvest of outbreak cages will remove one source of virus. However, ISA negative cages (C) that remain on the positive farm may potentially act as a viral reservoir.

Estimated prevalence of Aerococcus viridans and Anophryoides haemophila in American lobsters Homarus americanus freshly captured in the waters of Prince Edward Island, Canada.

The Canadian lobster industry holds lobsters Homarus americanus in captivity for various periods to supply markets with live product year-round. Mortality during holding results in considerable losses, estimated at 10 to 15 % yr(-1) by the industry. This study examined the prevalence of Anophryoides haemophila and Aerococcus viridans, causative agents of 'bumper car' disease and gaffkemia, respectively, in lobsters freshly captured in the waters of Prince Edward Island during the spring and fall fishing seasons of 1997. A total of 116 lobsters were sampled in the spring, and 138 in the fall. A. haemophila was not detected in the spring, while the prevalence was 0.72 % in the fall with a 95% confidence interval (CI) of 0.02 to 3.97% and an overall prevalence of 0.39% (95% CI: 0.01 to 2.17%). The prevalence of A. viridans was estimated at 6.9% (95% CI: 3.0 to 13.14%) in the spring, 5.8% in the fall (95% CI: 2.54 to 11.10%), and 6.30% overall (95% CI: 3.64 to 10.03%). Because of the reduced interest in food of diseased lobsters, and compromised metabolism in the case of gaffkemia, these prevalence estimates are likely underestimates of the true prevalence of gaffkemia and 'bumper car' disease in the wild populations of lobster around Prince Edward Island.

A dual infection of infectious salmon anaemia (ISA) virus and a togavirus-like virus in ISA of Atlantic salmon Salmo salar in New Brunswick, Canada.

Two viruses, infectious salmon anaemia (ISA) virus and a novel togavirus-like virus, were isolated from ISA disease outbreaks that were first reported as a new syndrome, haemorrhagic kidney syndrome (HKS) affecting farmed Atlantic salmon Salmo salar L. on the East coast of Canada. Laboratory confirmation of ISA diagnosis was initially complicated by isolation of only the togavirus-like agent using the CHSE-214 cell line. Here we demonstrate that a clinical sample from a disease outbreak of ISA contained a mixture of ISA virus and togavirus-like virus. Reverse transcriptase-polymerase chain reaction (RT-PCR) confirmed the presence of both viruses during serial passage of cultures in SHK-1 and CHSE-214 cells. Virus harvested at passage level 3 in both cell lines caused high mortalities and severe gross pathology consistent with ISA virus infection in experimentally inoculated Atlantic salmon parr (approximately 35 g) in freshwater, beginning 12 d post inoculation. ISA virus was detected by virus isolation from kidney and liver tissues of all dead or moribund fish tested. A comparison of virus isolation, 1-step procedure RT-PCR and RNA dot-blot hybridization for detection of ISA virus (ISAV) in fish tissues showed virus isolation to have 100% sensitivity, followed by RT-PCR (66 and 28% sensitivity in kidney and liver, respectively), with RNA dot-blot hybridization as the least sensitive method (20 and 10% sensitivity in kidney and liver, respectively). No togavirus-like virus was detected in these samples by virus isolation. Moreover, another togavirus-like virus isolate grown in CHSE-214 cells in the absence of any other detectable pathogen was non-pathogenic in experimentally inoculated fish. This study confirms that the original ISA outbreaks in New Brunswick, Canada, were caused solely by ISAV.

Growth of infectious salmon anaemia virus in CHSE-214 cells and evidence for phenotypic differences between virus strains.

Infectious salmon anaemia virus (ISAV) is a new orthomyxovirus-like virus. Thirteen isolates of ISAV (11 from Canada, one from Norway and one from Scotland) were studied for their replication in the CHSE-214 cell line compared with that in the SHK-1 cell line. All isolates replicated in SHK-1 cells, producing CPE between 3 and 12 days post-inoculation (p.i.). Six Canadian isolates also replicated in CHSE-214 cells, with production of CPE between 4 and 17 days p.i. Analysis of a one-step growth curve of ISAV in CHSE-214 cells showed that progeny virions remained predominantly cell-associated, accounting for the focalized nature of the CPE in the cell monolayer. One isolate (HKS 36) replicated in CHSE-214 cells, as shown by positive RT-PCR results of blind passages, but was non-cytopathic. All of the isolates were analysed for genetic heterogeneity by RT-PCR and RFLP with EcoRI and XhoI in a fraction of genome segment 2. The Canadian isolates showed a different RFLP profile to those of isolates Glesvaer/2/90 from Norway and 390/98 from Scotland. Structural proteins of four isolates, 'Back Bay 98', RPC/NB-877, RPC/NB-049 and Glesvaer/2/90, were examined further by SDS-PAGE. All viruses showed four major polypeptides, designated here as VP1-VP4, in Coomassie blue-stained gels. In isolates Glesvaer/2/90 and RPC/NB-877, these viral proteins had estimated molecular masses of 74, 53, 46 and 26.5 kDa, respectively. Viral proteins in isolates 'Back Bay 98' and RPC/NB-049 were of similar sizes, except that VP3 was 43 kDa. Taken together, these results show that there are phenotypic differences among strains of ISAV.

Drugs in salmonid aquaculture--a review.

In contrast to mammalian therapeutics, the use of pharmaceutical substances is rather limited in fish. It is basically restricted to anaesthetic agents and anti-infective agents for parasitic and microbial diseases. Anaesthetic agents are used primarily in fish farm and laboratory settings to provide analgesia and immobilization of fish for minor procedures. The anti-infective agents are used for controlling diseases and the choice of drug depends on efficacy, ease of application, human safety, target animal safety including stress to the fish, environmental impact, regulatory approval, costs, and implications for marketing the fish. In this article, the major drugs used in salmonids in North America and Europe will be reviewed and some insight into future directions for drug development and use for the salmonid industry will be introduced. The mechanisms of action, pharmacokinetics, side effects, and uses of the drugs are emphasized.