2018
Regional Update.
Gill Disease in Ireland: 2017 Update
Mar Marcos-López, Felix Scholz, Susie Mitchell, Hamish Rodger | Fish Vet Group Ireland
Amoebic gill disease (AGD) is considered endemic in Atlantic salmon mariculture in Ireland, and recurrent AGD outbreaks occurred in all sites except one during 2017. Macroscopic AGD pathology in older fish or in fish showing complex gill disease may not present itself as discrete white mucoid patches but more as diffuse gill paleness. This complicated the gross AGD gill scoring in some cases, and histopathology was required to assess disease severity. At present, freshwater baths represent 80-90% of the AGD treatments carried out in Ireland, while the remaining 10-20% are hydrogen peroxide treatments. In cleaner fish, AGD was diagnosed in wrasse and lumpfish in salmon pens, and in reared lumpfish in hatcheries. AGD was a significant factor in lumpfish mortality both at sea and in land-based facilities. Affected fish in hatcheries ranged from 0.2 g to broodstock, and several freshwater and hydrogen peroxide treatments were carried out. The macroscopic examination or gill scoring for AGD in lumpfish is significantly more challenging than in Atlantic salmon due to the opercular anatomy of lumpfish and the small size of some of the affected fish. A PCR screening program for Neoparamoeba perurans is recommended in lumpfish. Proliferative gill disease (PGD) is a chronic presentation of gill damage frequently encountered in cases of complex gill disease (CGD). CGD is of multifactorial origin and associated factors include infectious (i.e. N. perurans, Ca. Branchiomonas cysticola, salmon gill poxvirus, Desmozoon lepeophtheirii) and/or noninfectious (i.e. zooplankton, biofouling organisms, phytoplankton) agents. PGD was observed less frequently during 2017 than in 2016, and in most cases environmental causes were considered as the primary aetiology. Large Pelagia noctiluca swarms affected several sea sites in late summer and autumn 2017. Moderate to severe, mostly acute, mortalities were recorded in four sites, with significant stock losses occurring in two of the sites. Significant gill and skin damage were observed in the affected fish. Significant gill bleeding was observed in one site due to high numbers of Muggiaea atlantica and Radiolaria sp. Background, low level, gill damage consistent with water-borne insult was noted during routine examination in most sites.
Update: Gill disease in Scotland
Iain Berrill | Scottish Salmon Producer’s Organisation
Amoebic gill disease has been a health challenge for the Scottish farmed salmon sector since 2011. In response, the sector has developed protocols for monitoring, the sharing of information and management. The management of AGD is now greatly improved. However, in recent years the focus has shifted to a wider range of gill health challenges, covered by the umbrella term “complex gill disease”. The management of CGD is complex, and closely associated with the management of other health challenges, notably sea lice. This presentation will give a brief and broad overview of gill health and management activities undertaken in Scotland since 2011, with an insight into upcoming research.
An Update on Gill Health in Norway – 2017
Anne Gerd Gjevre | Norwegian Veterinary Institute
In 2017 Norway produced 1 207 800 tons of Atlantic salmon and 60 000 tons of rainbow trout. Estimated production of other marine species like cod, halibut, char and turbot were around 6000, 1600, 500 and 300, respectively. Additionally, 27-30 millions of lumpfish and 1.0-1.2 ballan wrasse were bred for use as cleaner fish. Since none of the gill diseases are notifiable in Norway, the Norwegian Veterinary Institutes (NVI) data are based on a survey conducted in connection with the annual Fish Health Report. In 2017, 34 persons from 17 private companies and 18 inspectors from Norwegian Food Safety Authority participated in this survey. During 2017 the NVI investigated gill disease in approximately130 on-growing and 20 smolt producing farms. Most often several gill pathogenic agents are present in the gill tissue. Complex or multifactorial gill disease, are ranged as a severe problem in Norwegian salmon farming in 2017, especially in the south-western part of the country.
Amoebic gill disease (AGD)
AGD is established as a severe disease in farmed Atlantic salmon in Norway. In 2017 AGD was ranged as one of the most important fish diseases of salmon in the southern part of Norway. Paramoeba perurans was detected from the counties Vest-Agder to Nordland. However, so far AGD is not detected further north than Nordland county. The severity of the disease differs from year to year. However, our impression is that the situation has been stabilized the last three years. The different regions have different strategies for disease management. Both fresh water and H2O2 have been used for treatment. In 2017 some regions started the treatments a bit earlier than in 2016 (Nordmøre, Sør-Trøndelag), while others started a bit later (Romsdal). In the counties Rogaland and Hordaland very few treatments were performed. Regularly scoring of typical lesions in the AGD season is an important tool to control the disease. However, after several treatments of the fish, the results might be a bit difficult to interpret due to other gill insults. Other agents in addition to P. perurans are often present when fish get an AGD diagnosis.
Salmonid gill poxvirus (SGPV) and other gill pathogenic agents
In 2017 the NVI detected SGPV as the causal agent for gill disease in eight smolt producing and eight ongrowing salmon farms in Norway. It’s difficult to know the real impact of this virus on gill disease, because a lot of screening as well as disease investigations are carried out by private laboratories. Infection by SGPV is also reported from Scotland and the Faeroe Islands, and the experiences are much the same.
In 2017 the epiteliocyst-forming agent ’Ca’ Branchiomonas cysticola are reported as a problem in some smolt producing farms as well as the microsporidion Desmozoon lepeophtherii.
Gill health overview in the Mediterranean aquaculture context
Albert Giron | ICTIOVET S.L., Provenza 392 PB. 08025 Barcelona, Spain | www.ictiovet.com
Gill pathologies are a relevant problem in Mediterranean aquaculture affecting both main cultured fish species in the Mediterranean (i.e. European sea bass and gilthead sea bream) with an estimated annual production close to 400K Tm causing production losses including direct mortalities. Gill parasites often have a role in gill pathology in Mediterranean species. Monogeneans are highly prevalent. Sparicotyle chrysophrii is the most relevant gill parasite affecting sea bream. In sea bass, prevalence of monogeneans Diplectanum spp is also high but, in some production areas in western Mediterranean, the copepod Learnonthropus kroyeri is probably the most remarkable gill parasite affecting sea bass. Other parasites that may appear associated to gill pathology are Amylodinium, Trichodina spp., Cardicola, amoebas and marine costia. However, these are often regarded as secondary infections and become a remarkable problem in specific production systems or early fish stages. Bacterial agents are involved in gill pathology too. Filamentous bacteria Tenacibaculum spp. are often involved in severe gill pathology. Intracellular prokaryotes Epitheliocystis are commonly detected in gills. Vibrio spp and Aeromonas salmonicida infections may also involve gill pathology in Mediterranean species. Non-infectious agents are also a problem in Mediterranean aquaculture and increased zooplankton numbers (Muggiaea spp and Ectopleura larynx) are correlated with gill pathology. According to our experience, European sea bass is more susceptible to such agents than sea bream. Mixed gill pathology is a common scenario in sea bream and sea bass making treatment challenging. Limited treatment options are available. These are discussed, as well as, control and monitoring measures under field conditions.
Update: Gill Disease in Chile
Jaime Santana | Camanchaca SA
Gill disorders have been a significant problem in the last decade for the Atlantic Salmon producer countries. The main losses have been associated with increases in mortality, poor growth and fish culled. Chile has not been oblivious to these issues, the main problems are infectious diseases (parasites, bacteria) and non-infectious diseases (HAB's and zooplankton bloom). Within the main pathologies are Proliferative Gill Disease (PGD) or Gill Complex (GC), pathologies with multifactorial etiology, and another hand, Amoebic Gill Disease (AGD), caused by Neoparamoeba perurans.
The presence of these disorders are increasing in the last 5 years, as also wide geographical spreading and severity, so that having surveillance systems is a useful tool for epidemiological understanding of diseases, and in this way establish the best practices, improve preventive measures and control, with the aim of reducing losses.
Keynotes.
Amoebic Gill Disease – UTAS research update
Barbara Nowak | IMAS UTAS Tasmania | Australia
Amoebic Gill Disease continues to affect farmed salmon and other fish species worldwide. This presentation will review AGD research progress at University of Tasmania in the last 12 months, including treatment and effects of environmental conditions on AGD.
Evaluation of viability is an essential requirement to screen in vitro treatments, assess infectious dose or investigate effects of environmental factors on amoebae. We compared a number of viability tests to determine best option for Neoparamoeba perurans. We then tested a number of treatments in vitro and evaluated the most promising one in vivo. We investigated in vitro and in vivo effects of short-term exposure to fresh water on N. perurans to examine if freshwater bathing could be replaced by short-term exposures. Effects of hypoxia on AGD were assessed through analysis of N. perurans loads and severity of AGD.
Harmful Algal Blooms: near real-time and forecast information for the aquaculture industry
Joe Silke, Caroline Cusack | Marine Institute | Ireland
Certain species of microscopic marine algae can accumulate into large blooms that cause mortalities in shellfish and finfish. Some contain a toxic irritant that results in damage to the gills of shellfish, fish and invertebrates. This, coupled with reduced oxygen levels during the decaying bloom can result in extensive mortalities over large areas of the coastline. In certain aquaculture operations these events can lead to highly stressed fish and in some cases mortalities ensue. This has been reported several times in Irish waters with significant episodes reported in 2005 and 2012. These blooms are part of the natural cycle of phytoplankton in the sea, and often originate offshore. As they are pushed to the coast by oceanic and tidal currents they accumulate to dense levels that can even discolour the seawater in what are often called ‘Red Tide’ events. Just as certain land plants contain toxins and irritants, so can certain marine algal species. The accumulation of these coastal blooms are usually not associated with pollution or any man induced activity. The duration of these blooms are difficult to predict, they may subside quickly to be replaced by the more typical mixed summer algal community, or may continue over several months. The Marine Institute operate a continuous programme to monitor seawater from coastal regions and all results are on the website immediately after analysis at www.marine.ie/habs . Recent Marine Institute research projects have focussed on the provision of advisory products to assist fish farmers with decision making regarding their day to day operations. These projects incorporate a range of data products that are combined to provide an informed judgement regarding the likelihood of a harmful bloom arising in the short term.
Salmonid Gill Disease in Freshwater
Hamish D. Rodger | fish vet group | Ireland
Gill disease of salmonids in freshwater is a high priority health concern which has been increasing in prevalence and impact in recent years in countries such as Norway and Scotland. The aetiologies include infectious and non-infectious elements which when coupled with changes in management and rearing methods appear to be giving rise to higher levels of direct impact in freshwater. In addition, the history of salmonid gill health in freshwater has short term and, it is considered, longer term effects for the fish in the marine environment. The pathogens, fish, environmental and management factors involved will be presented.
Breeding for AGD resistance: 14 years of experience in Australia
Mat Cook |commonwealth Scientific & Industrial Research Organisation | Australia
Amoebic Gill Disease (AGD) has been an ever-present burden on the culture of Atlantic salmon in Tasmania, Australia. In 2004, Saltas and CSIRO collaborated to develop a selective breeding program (SBP) for the industry. Front and centre of this program was the goal to breed for AGD resistance. This had not been attempted anywhere prior to this and required the appropriate R&D methodology, one which worked hand in hand with an industrial scale breeding program. Our experience over 14 years has demonstrated that AGD resistance is a heritable trait and significant gains can be made through a targeted goal driven breeding program. This talk will present aspects of the journey including the lessons learnt and the scale of the endeavour. It will also touch on the next frontier of breeding for disease resistance, genomic selection, and how that can be seamlessly rolled out into an industry scale operational breeding program.
Research Sessions.
Tenacibaculum maritimum associated with gill disease in Atlantic salmon in Norway
Stian Nylund | Pharmaq Analytiq | Norway
In 2017, as for previous years, the number of gill disease cases started to increase in the late summer- to autumn. The majority of these were concentrated in Western Norway, with numerous detections of known gill pathogens, such as Cand. `Branchiomonas cysticola´, Paranucleospora theridion, Paramoeba perurans and Salmon gill poxvirus (SGPV). In many cases most of the pathogens would be present at the same time, and histological examinations typically included observations of gill inflammation, proliferation, necrosis and epitheliocystis. Classical AGD lesions with patchy, severe proliferation was only seen when amoeba were present. In late autumn, a new clinical sign, with associated mortality, started to appear in Atlantic salmon suffering from severe gill disease in the sea- phase. Several individuals were observed having yellow mucoid patches on the gills in addition to the typical damages seen before. From histological sections, these yellow patches showed presence of filamentous bacteria resembling Tenacibaculum. Tenacibaculum species are well known to cause skin ulcers in Norwegian salmon, but this is the first time we see the bacteria associated with gill ulcers in Norway. Since gill ulcers related to Tenacibaculum maritimum has been observed in Canada, a new PCR-assay was developed for specific detection of T. maritimum, which gave a clear positive result on the fish with gill ulcers. T. maritimum is a widespread- and known pathogen for Atlantic salmon in other salmon producing countries, but has not previously been identified on this species in Norway. A T. maritimum isolate has been associated with skin lesions in Norwegian lumpsucker, but the distribution and prevalence in production has not been investigated. It is not known if the isolate identified in Atlantic salmon and in lumpsucker in Norway are the same, or if they are similar to the isolates found in other salmon producing countries. To evaluate the importance and distribution of T. maritimum in Norwegian aquaculture, PHARMAQ Analytiq, along with partners, has started a research project partly financed by Innovation Norway. Since it is unknown if there is a link between the identification in lumpsucker and in Atlantic salmon, both species are included in the study. Preliminary results from screening of several gill disease cases in Atlantic salmon in 2017, and earlier years, as well as data from screening from lumpsucker production will be presented.
Characterization of gene expression in gills from a natural disease outbreak with Salmon Gill Poxvirus (SGPV)
Mona Gjessing | Aleksei Krasnov *| Gerrit Timmerhaus * | Svante Brun **| Sergey Afanasyev* | Ole B Dale | Maria K Dahle
Norwegian Veterinary Institute, Oslo, Norway | Nofima, Ås, Norway* | Marine Harvest Norway**
Salmon Gill Poxvirus (SGPV) represents the deepest branch of chordopoxvirus so far discovered. It is a large DNA-virus with more than 200 genes. In farmed Atlantic salmon gill disease due to this virus can result in very high, acute mortality. Most of the Norwegian outbreaks uncomplicated by other gill agents occur in certain fresh water facilities. SGPV infects gill epithelium and in diseased fish widespread apoptosis or severe epithelial hyperplasia appears to compromise respiration. During a natural outbreak in a hatchery gill samples were taken from three tanks with a similar disease course high mortality for three days. Samples from early infection phase, acute mortality phase and regenerative phase were analysed for SGPV with qPCR, histopathology and transcriptome analysis by microarray. The gene expression in the gills during acute phase correlated well with pathological changes. Upregulation of proapoptotic and proliferative genes was observed together with changed expression with respect to ionchannels and mucus proteins. The interferon regulated anti-viral response was significantly upregulated and closely correlated with the amount of SGPV in the gills. Chemokine expression changed dramatically over the time course studied, but the transcriptional data did not indicate any recruitment of lymphocytes and adaptive immunity response in the gills, including late regenerative phase. These data give new insights in the interaction between SGPV and the salmon host, and lead to identification of marker genes correlating with pathology and host immune response.
Ten-year survey of epitheliocystis in sea-farmed Atlantic salmon in Norway
Jannicke Wiik-Nielsen | Heidi T. Solheim | T.M. Steinum* | Saima N. Mohammad | Anne Berit Olsen | Geir Bornø | Hanne Ringkjøb Skjelstad | Duncan J. Colquhoun
Norwegian Veterinary Institute, Norway | Istanbul University, Turkey *
The aetiology of epitheliocystis in sea-farmed Norwegian Atlantic salmon from 72 geographically diverse diagnostic cases, sampled between 2005 and 2015, was retrospectively studied. Formalin-fixed, paraffinembedded tissues were investigated using standard histological techniques, in situ hybridisation, laser dissection microscopy, directed qPCR analyses and 16S gene sequencing. Successful fluorescence-based in situ staining of intracellular cysts utilising ‘universal’ bacterial probes (necessary to allow laser dissection microscopy), was achieved in 64 of the 72 cases investigated in which intracellular cysts were visible in haematoxylin and eosin stained sections. Following extraction of bacterial DNA from fluorescent stained cysts excised by laser dissection microscopy, specific qPCR analysis identified Ca. Branchiomonas cysticola in 54 (75 %) of the investigated cases, confirming this bacterium to be the main agent of epitheliocystis in Norwegian sea-farmed salmon. BLAST analysis of nearly full-length 16S rRNA gene sequences retrieved from representative Ca. B. cysticola qPCR-negative cysts, identified the aetiological agent to be a previously undescribed beta-proteobacterium displaying 89% identity with its closest ‘neighbour’ in public sequence databases and approximately 88% identity with Ca. B. cysticola. We propose the name Ca. Branchionella piscium for this novel agent of epitheliocystis. A qPCR analysis developed to specifically identify Ca. B. piscium confirmed its presence within the 10 remaining cases in which we could not identify Ca. B. cysticola within the cysts. In addition, mixed infections involving Ca. B. cysticola and Ca. B. piscium were identified in 10 cases. While the ‘universal’ bacterial probes utilised in the present study identify a very wide range of bacterial taxa, they are not suitable for all, including Chlamydia-related organisms. We are now working towards characterisation of the agents within cysts not stained by the ‘universal’ probes. So far, we have however, added another member to the list of bacterial agents responsible for epitheliocystis in sea-farmed Atlantic salmon. Of the 64 cases in which epitheliocysts could be fluorescently stained, ~69 % were associated with Ca. B. cysticola alone, ~16 % with Ca. B. piscium alone and ~15 % with mixed infections of the two bacteria.
Insights into the role of Desmozoon lepeophtherii in Atlantic salmon (Salmo salar L.) Complex Gill Disease.
Ana Herrero | Kim D. Thompson | Mark P. Dagleish | Marian McLoughlin| Hamish Rodger* | Chris Matthews*| Giuseppe Paladini **| James Bron **| Alexandra Adams ** |Oswaldo Palenzuela ***
Moredun Research Institute, Pentlands Science Park, UK | Fish Vet Group, Inverness, UK * | Institute of Aquaculture, University of Stirling, UK **| Institute of Aquaculture, Torre de la Sal (IATS-CSIC), Castellón, Spain ***
The microsporidian Desmozoon lepeophtherii (syn. Paranucleospora theridion) has been suggested by several authors to play a major role in the pathogenesis of complex gill diseases. Although the parasite may have a high prevalence in apparently healthy salmon by real time polymerase chain reaction (qRTPCR), studies have demonstrated that parasite densities are significantly higher in fish suffering from gill disease. Despite the parasite having been shown to be detrimental to farmed Atlantic salmon the exact role it plays is still unknown due to the difficulty in detecting the parasite under light microscopy. Microsporidian parasites are intracellular and relatively small organisms (1-20 μm in diameter). Conventional histological techniques only allow the visualization of the spore stage of D. lepeophtherii which, in salmon, is generally dispersed at low density throughout the tissues making it difficult to confirm their presence in tissue sections. An in situ hybridization (ISH) protocol with DIG-labeled oligonucleotide probes designed from SSUrRNA and internal transcribed spacer (ITS) specific for D. lepeophtherii was established with the aim of detecting all life-stages of the microsporidian. We analyzed different farmed Atlantic salmon with gill disease cases in Scotland using haematoxylin and eosin (H&E), Calcofluor White and ISH to compare the sensitivity of each detection method for the presence of spores and proliferative stages of the parasite in tissue sections and determine pathogen – lesion association. The results obtained to date will be presented and discussed.
Common sampling artefacts in gill histology
Susie Mitchell | Mar Marcos-López | Felix Scholz | Hamish Rodger | Fish Vet Group Ireland
Histopathology is the analysis of very thin tissue sections under the light microscope for diagnostic or research purposes. The presence of artefacts on histological sections can result in misinterpretation of findings and inaccurate diagnosis. Artefacts due to incorrect handling of the samples can occur at each of the steps of the histology process (i.e. biopsy, fixation, processing, sectioning and staining). The most common encountered artefacts for diagnosticians are those resulting from inappropriate euthanasia and sample collection. Morphological alterations due to sampling artefacts (e.g. delayed sampling postmortem, forceps-induced damage) on gill histology sections and best practices for the collection of gill histology samples will be discussed in the presentation.
Pox virus in Atlantic salmon – Tracing of infection in salmon and samples from the environment, decontamination and possible vertical transmission.
Mona Gjessing | Even Thoen | Ole Bendik Dale | Maria K Dahle | Trude Marie Lyngstad | Simon Weli | Brit Tørud | Karoline Sveinsson | Snorre Gulla | Stian Nylund * | Renate Johansen*
Norwegian Veterinary Institute | Pharmaq Analytic *
After characterization of the salmon gill pox virus (SGPV) in 2015, the Norwegian Veterinary Institute confirmed 18 cases of Salmon gill pox virus disease (SGPVD) spread all over the country. The cases included first feed fry, smolt and post sea-transfer salmon. In 2015, 15 smolt farms and 3 sea locations were diagnosed with SGPVD. In 2016 the numbers were 11 and 9, respectively. In addition there may be cases examined by other laboratories. The SGPV may be the only agent present or part of a multifactorial gill inflammation. SGPV can also be found in healthy fish without any characteristic histopathological changes in the gills. To acquire more knowledge about SGPV infections the Norwegian veterinary Institute got funding for a 2year project from the Norwegian Seafood Research Fund. The project is organized into five work packages: WP1 investigate genetic components and establish new methods for tracing WP2 Find an effective way to detect SGPV in the environment WP3 Epidemiologic mapping of the infection WP4 Investigate effects of disinfection and fallowing (RAS) WP5 Investigate the possibility of vertical transmission Five hatcheries are included in the project and one or two groups from each hatchery is followed from the first feeding, during vaccination, sea transfer and after a period on the sea location. All the hatcheries have differences in their production methods, flow through or RAS, some with and some without addition of sea-water in the production period and with or without anadromous salmonids in the fresh water sources. More details and preliminary results will be presented.
CERES: The potential impact of climate change on salmon aquaculture
Tom Doyle, NUI Galway/UCC, Ireland, Hamish Rodger, Mar Marco-Lopez (Fish Vet Group), Natalie Angelopoulos, Katie Smyth (University of Hull), Susan Kay (Plymouth Marine Laboratory)
The CERES Project is investigating how climate change will influence Europe’s most important fish and shellfish resources and the economic activities depending on them. It will provide tools and develop adaptive strategies allowing fisheries and aquaculture sectors to prepare for adverse changes or future benefits of climate change. This talk will present climate model projections for sea surface temperature in the North East Atlantic for 10, 30 and 50 years’ time. I will discuss some potential climate change impacts on the salmon industry and use a mapping exercise to illustrate these impacts and finally ask for audience participation to improve this model process. This mapping exercise will be used to identify the specific risks and potential mitigation measures of climate impacts from both an industry and policy perspective.
Jellyfish blooms and caged salmon
Anna Kintner | Europharma
Although widely covered in the media, jellyfish blooms and salmon farm interactions are poorly characterized and understood, and aquaculture industry tools for mitigating them are lacking. This talk will cover the essential concepts and biological principles behind blooms and present state of knowledge relevant to salmon aquaculture, including life cycle, seasonal drivers of jellyfish population, and mechanisms of causing gill damage. We will identify the major challenges we face in managing jellyfish blooms, and discuss what information we need to address them effectively. Finally, we will cover the challenges in developing this information, and suggest effective research methods for the future.
The adherent microbial community of jellyfish: Isolation of harmful bacteria and their implications for the aquaculture industry.
Morag Clinton | University of St. Andrews, Scotland
There is much still to be learnt regarding the impact of trauma to farmed fish from the Cnidarian species commonly referred to as jellyfish, particularly the consequences of exposure in delicate gill tissue. We investigated the adherent microbial community of three species of jellyfish to determine if exposure of fish to jellyfish might also result in exposure of fish to known bacterial pathogens. Sequencing was focused on genera known to contain pathogenic species, specifically Aeromonas, Vibrio and Pseudomonas. A number of bacteria with the potential to cause disease in farmed fish were identified. This talk will present the results of research conducted at the University of St Andrews by Morag Clinton as well as discuss the discuss the implications not just for the health of Atlantic salmon, but also other commercially important specie utilised in Atlantic salmon production.
(Expected publication of this work alongside previous research by co-author Anna Kintner 2018).
The influence of fronts on the advection of harmful jellyfish blooms
Damien Haberlin | University College Cork, Ireland
Thermohaline fronts are a ubiquitous phenomenon across continental shelf seas that are known to enhance primary productivity and aggregate biomass. The enhanced productivity at fronts provides favourable conditions for higher trophic levels, however, the influence on gelatinous zooplankton is poorly understood. Sampling carried out during July 2015 found two distinct gelatinous communities across the Celtic Sea Front; an Irish Sea community in the cooler mixed water which was largely composed of neritic taxa, and a Celtic Sea community in the warmer stratified water which contained a mixed neritic and oceanic community. The gelatinous abundance (656 indiv. m-3) and biomass (2085 mg C 1000 m-3) was higher in the Celtic Sea and was dominated by Aglantha digitale, Lizzia blondina and Nanomia bijuga. The mean gelatinous contribution to the total zooplankton biomass was 4 - 6%, reaching a maximum of 16% in the Celtic Sea. Physonect siphonophores were surprisingly widespread, contributing >25% of the gelatinous biomass, suggesting their ecological importance is underestimated. Multivariate analysis of the zooplankton biomass indicates that water column structure, coupled to the underlying topography, is the key driver of variation in the zooplankton community. There was no evidence that the Celtic Sea front aggregated harmful jellyfish species, however, it is likely that the front influences the seasonality and abundance of harmful species in Irish coastal waters.
Virulence factors associated with Neoparamoeba perurans
Kerrie Ni Dhufaigh | Galway Mayo Institute of Technology, Ireland
Neoparamoeba perurans is the causative agent of Amoebic Gill Disease characterised by hyperplasia on the secondary gill lamellae of infected hosts, leading to serious economic loss. Despite many years of study, virulence factors and the mechanisms of the infection process remain unknown. In this study a comparative proteomic approach through two-dimensional gel electrophoresis is used to analyse differential protein expression between two N. perurans isolates (putatively avirulent and virulent strain) with the goal of identifying proteins associated with virulence.
RAS and impacts on gill disease
Mark Powell | Institute of Marine Research, Norway
Recirculating Aquaculture Systems (RAS) have become increasingly important in the production of juvenile fish, particularly salmon smolts. The principles of recirculating water (in excess of 90%), to reduce the total water usage and maximize production through high production densities are highly dependent upon the implementation of well-functioning and adequately dimensions technology. The water quality of the make-up water (less than 10% of water used in the system) plays a vital role in fish health and, in particular, the vulnerability of gills. Similarly, the microbial environment becomes enhanced with high fish production densities, high organic loading of the water and increasingly depended upon the functioning of the RAS treatment technology. Discussion of the role of elevated carbon dioxide levels, suspended solids, nitrogen loading, and operational biosecurity will relate to the risk for reduced gill health and highlight areas where much needed further investigation is required.
Reviewing fish safety in hydrogen peroxide treatments
Amund Litlabø | Madeline French * | Stian Aaen *
Aqua Pharma | Solvay AS *
Hydrogen peroxide (H2O2) has been used as anti-parasitic treatment in salmonid aquaculture since the mid 1990’s. Initially applied to remove the ectoparasites Lepeophtheirus salmonis and Caligus spp., but in the later years also to combat Paramoeba perurans. H2O2 treatment is performed in the seawater phase, either in well boats or directly in the cage. To optimise treatment concentration and to secure even dispersal of the compound, tarpaulins surround the cages during treatment. Field experience using Aqua Pharma treatment systems Hydrogen peroxide is applied in large quantities, which requires specialist equipment and logistics. With the current aquaculture farm design and large biomass, rapid dosing and effective dispersion to reach the therapeutic concentration is necessary. Aqua Pharma will share experiences from field treatments, considering differences between well boat and cage treatments in relation to fish safety. Literature review of laboratory and field experience Although a simple molecule, the use of hydrogen peroxide in both field treatments and laboratory experiments requires precautions to be taken. Experiences from field and laboratory use will be shared and common guidelines provided. Relevant fish physiological parameters both during and after treatment have been reviewed and will be considered in relation to environmental conditions. Challenges related to sea lice and AGD treatments will be discussed from a researcher’s viewpoint.
Peracetic acid as a potential treatment for amoebic gill disease (AGD) in Atlantic salmon PERAGILL
Carlo C. Lazado | Project Leader Nofima, Norwegian Institute of Food, Fisheries and Aquaculture Research
Besides sea lice infestation, amoebic gill disease (AGD) is a significant and daunting issue the Norwegian Atlantic salmon aquaculture industry is facing today. The first documented case of AGD in Norway was in 2006. Since then, the threats have been quite persistent and the number of reported cases is showing an upward trajectory trend. The industry must be kept abreast with sustainable treatment options to combat this emerging threat.
This newly-funded project will explore the potential of peracetic acid (PAA), an organic peroxide, as an alternative treatment for AGD. PAA offers some advantages that may address the challenges in the currently available treatments for AGD. First, it degrades completely within several hours after application and results in harmless residues. Second, the effective concentration of PAA is less than 2 mg L−1 against various pathogens, in contrast to hydrogen peroxide that needs a much higher concentration to achieve successful disinfection. Third, PAA application has little impact on fish health, and if there are oxidative changes following application, this can be easily addressed by manipulating the mode of application. Fourth, PAA products are potentially suitable disinfectants for recirculating integrated multi-trophic aquaculture systems because some non-target organisms are not susceptible to treatment. Fifth, exposure to PAA at concentrations less than 1 mg L-1 had no severe impact on biofilter performance, hence, addressing issues on system disturbance and applicability in production system operating in RAS technology (e.g., closedcontainment system). And most importantly, PAA exhibits anti-parasitic effects.
PERAGILL is organised into 5 Work Packages (WPs). WPs 1-3 constitute the STAGE I while WPs 4-5 are part of the STAGE II. WP1 is the backbone of the project and together with WP2, will lay the foundation for WPs 4-5. WP1 will explore the effects of PAA on the causative agent and on the host, WP2 will evaluate the environmental risk associated with PAA treatment, WP4 will investigate different PAA application strategies to treat AGD infection and WP5 will compare the efficacy of PAA with the two conventional AGD treatments. WP3 constitutes the toolbox that will be used to assess the effects and efficacy of the treatment and will bridge STAGES I and II. The integration of traditional and modern approaches and tools would facilitate the development of a toolbox that will be valuable in future research concerning AGD treatments, especially with the use of oxidative disinfectants.
SKRETTING ARC PROTEC GILL R&D UPDATE
J. Mullins | B. Nowak * | M. Leef * | A. Holzer ** | Ø. Røn | C. McGurk
Skretting Aquaculture Research Centre, Stavanger, Norway | University of Tasmania, Launceston, Australia * | Biology Centre of the Academy of Sciences of the Czech Republic, Ceske Budejovice, Czech Republic **
Amoebic gill disease (AGD) caused by Paramoeba perurans is the leading cause of gill disease in Atlantic salmon worldwide. Despite more than 30 years of research, there are no vaccines or medicines licensed to treat AGD. There is an opportunity through diet to potentially alter both the physical and qualitative characteristics of fish mucus, and in turn influence the survival of fish affected with AGD. An in vitro plate assay was developed to screen and identify prospective compounds for inclusion in diets and to evaluate the effects of mucus collected from Atlantic salmon fed these compounds. Dietary effects of these ingredients were then assessed through fish survival and selected biomarkers in Atlantic salmon experimentally infected with P. perurans. Further, the same compounds were also fed to non infected fish to assess their effects upon mucus characteristics.
Experimental results showed that diet has the potential to play an important role in the management of AGD by improving fish survival, enhancing mucus defences, reducing gill damage and reducing amoebae survival.
Key points of impact:
P. perurans survival was significantly reduced by direct and indirect exposure to specific compounds compared to controls.
Experimental diets significantly increased survival of Atlantic salmon challenged by P. perurans compared to control diets.
Mus samples collected from fish fed Protec Gill had higher viscosity and lysozyme levels than mucus from control fed fish.
Feeding Protec Gill after an algal bloom gave faster reduction in gill scores and improved gill immunity.
Genotype-by-ploidy interaction in AGD resistance in Atlantic salmon
Richard Taylor | Matthew Hamilton | Brad Evans *| Peter Kube | Klara Verbyla | Harry King
CSIRO Agriculture and Food | Salmon Enterprises of Tasmania (SALTAS)*
The Tasmanian Atlantic salmon industry uses 100% all-female stocks in order to control the high levels early maturation (grilsing) that would be expected with normal mixed-sex animals. Approximately 20% of current production is based on all-female triploid stock. The Salmon Enterprises of Tasmania (SALTAS) salmon selective breeding program (SBP) was established in 2004. The breeding nucleus is managed as mixed-sex and trait estimates for AGD resistance, weight and other important commercial traits are based upon diploid stocks. This presentation describes a field experiment to test genetic parameters between sibling all-female diploid and triploid fish. 200 families were produced from four neomales (genetic females that had masculinised as fry using 17methyltestosterone) each crossed with 50 normal females. Half of the resultant fertilised eggs were triploided by pressure shock. The diploid and triploid offspring were individually weighed and PIT tagged and sent to sea on a commercial fish farm 15 months later. The fish were allowed to develop natural AGD and were gill scored and freshwater bathed three times with three marine weight measures. Narrow sense heritability measures for AGD and growth were in line with previous SBP measures. Interploidy genetic correlations were moderate to high for AGD, therefore there is not a strong argument for the development of a separate triploid breeding objective. Strong inter-ploidy correlations for weight indicate that breeding for weight in diploids would be expected to result in substantial gains in triploids assuming both are grown in a similar environment.
Optimisation of a new method to extract genetic material from microbes on gills. First step of an early Amoebic Gill Disease detection
Victor B. Birlanga | Microbiology Department, National University of Ireland (Galway), Ireland (v.birlanga1@nuigalway.ie)
Amoebic Gill Disease (AGD) is associated with marine farmed Atlantic salmon (Salmo salar L., 1758) and has been observed to reach over 50% in some stocks in Tasmania [1]. Its presence was first confirmed in Ireland in 1996 [2], becoming a primary salmonid health concern in Europe. At present, the only way to reduce AGD impact on fish stocks is to rigorously control its presence and development. All current procedures for determining AGD presence and stage are based on detecting and/or quantifying Neoparamoeba perurans (AGD first aetiological agent). But require AGD to be in an advanced stage to enable detection, thus preventing early diagnosis. Methodologies include: gill inspection, histology and N. perurans genetic tests [3]. As described previously [4, 5], the microbial community present on a biological tissue plays an important role in the development many diseases in all species. Therefore, characterizing the microbial community of farmed Atlantic salmon gills throughout different AGD stages may allow a correlation to be observed between microbial community and early AGD symptoms. In the present research, a new method is under development to isolate the microbial community of salmon gills, and to extract total microbial DNA and RNA using whole gill samples. This would allow us to characterize the abundance of the microbes present and to correlate them with different AGD stages. In brief, a combination of Trypsin washes and sonication was used to detach microbial cells from gill tissue. After a series of washes, a precipitation step was performed to accumulate genetic material and remaining microbes in a pellet. Subsequently DNA/RNA extractions was carried out using a commercial kit. Different parameters were measured before and after the most critical steps to ensure its optimisation. This protocol can be used for various sample types to characterize superficial microbial communities, and will be useful in detection of the early onset and treatment of AGD.