Infestation rates of lice Lepeophtheirus salmonis and Caligus elongatus on Atlantic salmon in fixed and towed sentinel cages.

Sea lice are a key limitation to sustainable salmon aquaculture, and effective monitoring strategies are critical for the management of these parasites. Sentinel cages are an established means of assessing infestation pressure at fixed locations, but as smolts move through systems they will be exposed to varying lice densities. As a means of assessing infestation pressure along trajectories, we describe the development and application of towed sentinel cages (TSCs) in a Scottish sea loch containing salmonid aquaculture. Trial deployments took place over 3 yr (2016-2018), and levels of sea lice infestation were compared between methodologies. Oceanographic data was collected alongside TSCs to put the results into the environmental context that smolts and sea lice experienced during the tows. The sea lice infestation rates found from TSCs were comparable to those on contemporaneously deployed fixed sentinel cages. Thus, due to their practicability and consistency with other surveillance methods, TSCs could be used to improve the assessment of exposure risk along wild salmonid smolt migration trajectories, where these are known.

Modelling temperature and fish biomass data to predict annual Scottish farmed salmon, Salmo salar L., losses: Development of an early warning tool.

Losses due to mortality are a serious economic drain on Scottish salmon aquaculture and are a limitation to its sustainable growth. Understanding the changes in losses, and associated drivers, are required to identify risks to sustainable aquaculture. Data on losses were obtained from two open source data sets: monthly losses of biomass 2003-2018 and losses of salmon over production cycles (numbers input minus output harvest) 2002-2016. Monthly loss rates increased, accelerating after 2010, while losses per production cycle displayed no trend. Two modelling frameworks were investigated to produce an early warning tool for managers about potential increases in losses. Both linear regression and beta regression showed that monthly losses related to biomass and minimum winter air temperatures with high precision and low bias. These relationships apply at both the national and regional levels where the beta regression best fit model explain 82 % and 69 % of variation in mortality, some regional differences apply, particularly for the Northern Isles. The lack of trend in losses per production cycle may have been due to shorter production cycles as more salmon were harvested earlier, and possibly increasing losses of larger salmon (which affects biomass but not numbers lost). In the long-term, the models predict that milder winters and increased biomass will be associated with increased mortality, which will need to be managed. In the short-term, given relatively little year-to-year variation in biomass, minimum winter temperature is a powerful early warning of the likely extent of losses in the Scottish salmon farming industry.

The contact structure of Great Britain's salmon and trout aquaculture industry.

We analyse the network structure of the British salmonid aquaculture industry from the perspective of infectious disease control. We combine for the first time live fish transport (or movement) data covering England and Wales with data covering Scotland and include network layers representing potential transmission by rivers, sea water and local transmission via human or animal vectors in the immediate vicinity of each farm or fishery site. We find that 7.2% of all live fish transports cross the England-Scotland border and network analysis shows that 87% of English and Welsh nodes and 72% of Scottish nodes are reachable from cross-border connections via live fish transports alone. Consequently, from a disease-control perspective, the contact structures of England and Wales and of Scotland should not be considered in isolation. We also show that large epidemics require the live fish movement network and so control strategies targeting movements can be very effective. While there is relatively low risk of widespread epidemics on the live fish transport network alone, the potential risk is substantially amplified by the combined interaction of multiple network layers.

A potential role for protein O-fucosylation during pollen-pistil interactions.

Putative protein O-fucosyltransferases (POFTs) represent a large family of Glycosyl Transferase family 65 domain-containing proteins in land plants, with at least 39 proposed members in the Arabidopsis thaliana genome alone. We recently identified a member of this family, AtOFT1 (At3g05320), in which loss-of-function mutants display impaired sexual reproduction that was linked to a defective male gamete. Specifically, oft1 mutant pollen tubes are ineffective at penetrating the stigma-style interface leading to a drastic reduction in seed set and a nearly 2000-fold reduction in pollen transmission. Our findings establish that AtOFT1 plays a critical role in pollen tube penetration through the stigma/style in Arabidopsis and further suggest an important role for protein O-glycosylation events that potentially influence pollen tube mechanical strength or the ability to respond to positional guidance cues during the process of tube growth and fertilization.

A historical review of the key bacterial and viral pathogens of Scottish wild fish.

Thousands of Scottish wild fish were screened for pathogens by Marine Scotland Science. A systematic review of published and unpublished data on six key pathogens (Renibacterium salmoninarum, Aeromonas salmonicida, IPNV, ISAV, SAV and VHSV) found in Scottish wild and farmed fish was undertaken. Despite many reported cases in farmed fish, there was a limited number of positive samples from Scottish wild fish, however, there was evidence for interactions between wild and farmed fish. A slightly elevated IPNV prevalence was reported in wild marine fish caught close to Atlantic salmon, Salmo salar L., farms that had undergone clinical IPN. Salmonid alphavirus was isolated from wild marine fish caught near Atlantic salmon farms with a SAV infection history. Isolations of VHSV were made from cleaner wrasse (Labridae) used on Scottish Atlantic salmon farms and VHSV was detected in local wild marine fish. However, these pathogens have been detected in wild marine fish caught remotely from aquaculture sites. These data suggest that despite the large number of samples taken, there is limited evidence for clinical disease in wild fish due to these pathogens (although BKD and furunculosis historically occurred) and they are likely to have had a minimal impact on Scottish wild fish.

A survey of wild marine fish identifies a potential origin of an outbreak of viral haemorrhagic septicaemia in wrasse, Labridae, used as cleaner fish on marine Atlantic salmon, Salmo salar L., farms.

Viral haemorrhagic septicaemia virus (VHSV) was isolated from five species of wrasse (Labridae) used as biological controls for parasitic sea lice predominantly, Lepeophtheirus salmonis (Krøyer, 1837), on marine Atlantic salmon, Salmo salar L., farms in Shetland. As part of the epidemiological investigation, 1400 wild marine fish were caught and screened in pools of 10 for VHSV using virus isolation. Eleven pools (8%) were confirmed VHSV positive from: grey gurnard, Eutrigla gurnardus L.; Atlantic herring, Clupea harengus L.; Norway pout, Trisopterus esmarkii (Nilsson); plaice, Pleuronectes platessa L.; sprat, Sprattus sprattus L. and whiting, Merlangius merlangus L. The isolation of VHSV from grey gurnard is the first documented report in this species. Nucleic acid sequencing of the partial nucleocapsid (N) and glycoprotein (G) genes was carried out for viral characterization. Sequence analysis confirmed that all wild isolates were genotype III the same as the wrasse and there was a close genetic similarity between the isolates from wild fish and wrasse on the farms. Infection from these local wild marine fish is the most likely source of VHSV isolated from wrasse on the fish farms.

An approach to evaluating the reliability of diagnostic tests on pooled groups of infected individuals.

An experimental design and statistical analysis providing information on the reliability of pooled test procedures is described. It involves estimating the relationship between the probability of a positive pooled test result (dependent variable) and the expected number of infected individuals in a pool (explanatory variable). The intercept is an estimate of the proportion of false positives (1-pooled specificity) and pooled sensitivities can be estimated for indicative prevalences of infected individuals. Simulations for a theoretical infection are used to investigate the advantages and limitations of the approach. The approach is used to evaluate the reliability of a virus isolation and qRT-PCR test procedure detecting Salmonid alphavirus the pathogenic agent necessary for the development of Pancreas Disease in Atlantic salmon (Salmo salar).

Detection of salmonid alphavirus RNA in wild marine fish: implications for the origins of salmon pancreas disease in aquaculture.

Salmonid alphaviruses (SAVs), which include the aetiological agents of salmon pancreas disease (SPD) in farmed Atlantic salmon Salmo salar L. and sleeping disease (SD) in rainbow trout Oncorhynchus mykiss (Walbaum), are significant viral pathogens of European salmonid aquaculture. SAV is horizontally transmitted and the virus can survive for extended periods in seawater. A lack of convincing evidence for vertical transmission coupled to the fact that the SPD virus (SPDV) occurs in historically infected sites irrespective of fallow period duration suggests that a substantial reservoir of infection exists in the marine environment. We used a highly sensitive real-time PCR (qPCR) assay targeting a region of the SAV nsP1 gene to screen wild marine fish species for the presence of SAV in an attempt to identify such a potential reservoir. Screened fish species were caught in the vicinity of aquaculture activity in an area with a previous history of SAV infection (Shetland Isles, Scotland). SAV RNA was detected in internal organs (kidney and heart) from the flatfish species common dab Limanda limanda, long rough dab Hippoglossoides platessoides, and plaice Pleuronectes platessa. Based on these findings, sampling was extended to an area remote from aquaculture activity (Stonehaven Bay, NE coast of Scotland) from where heart tissues obtained from common dab also tested positive. While no virus could be cultivated from these samples, qPCR detections were shown to be SAV-specific by sequencing of an alternative gene region (E2) to that targeted by the qPCR assay. Analysis of these nucleotide sequences revealed minor differences to those previously obtained from farmed salmon, and subsequent phylogenetic analysis of an E2 dataset demonstrated a subtype V-like sequence.

A water-specific aquaporin involved in aphid osmoregulation.

The osmotic pressure of plant phloem sap is generally higher than that of insect body fluids. Water cycling from the distal to proximal regions of the gut is believed to contribute to the osmoregulation of aphids and other phloem-feeding insects, with the high flux of water mediated by a membrane-associated aquaporin. A putative aquaporin referred to as ApAQP1 was identified by RT-PCR of RNA isolated from the guts of pea aphids Acyrthosiphon pisum. The ApAQP1 protein has a predicted molecular mass 28.94kDa. Molecular modeling suggests that ApAQP1 has the general aquaporin topology and possesses the conserved pore properties of water-specific aquaporins. When expressed in Xenopus oocytes, ApAQP1 showed the hallmarks of aquaporin-mediated water transport, including an 18-fold increase in the osmotic water permeability of the oolemma, a reduced activation energy, and inhibition of elevated water transport activity by Hg ions. The ApAQP1 transcript was localised to the stomach and distal intestine, and RNAi-mediated knockdown of its expression resulted in elevated osmotic pressure of the haemolymph. Taken together, these data suggest that ApAQP1 contributes to the molecular basis of water cycling in the aphid gut.

Distribution of infectious pancreatic necrosis virus (IPNV) in wild marine fish from Scottish waters with respect to clinically infected aquaculture sites producing Atlantic salmon, Salmo salar L.

This study represents the first large-scale investigation of IPNV in Scottish wild marine fish. Kidney samples were taken from 30 627 fish comprising 37 species and 45 isolations were made from nine different species, illustrating these as reservoirs of IPNV in Scottish waters. The estimated prevalence of IPNV in the Scottish marine environment was low at 0.15% (90% confidence intervals, (CI) of 0.11-0.19%). This was significantly greater in fish caught less than 5.0 km from IPN-positive fish farms in Shetland, at 0.58% (90% CI of 0.45-0.77%). This prevalence persisted and did not significantly decrease over the 16-month period of study. The estimated prevalence of IPNV for each positive species was less than 1% with the statistically non-significant exceptions of flounder, Platichthys flesus (L.), at 12.5% (90% CI of 0.64-47.06%) and saithe, Pollachius virens (L.), at 1.11% (90% CI of 0.49-2.19%). The 45 isolates were titrated and all but two were below the detection limit of the test (<55 PFU g(-1)). Titres of 3.8 x 10(2) PFU g(-1) and 2.8 x 10(1) PFU g(-1) were calculated from common dab, Limanda limanda (L.), and saithe, respectively. This study provides evidence that clinical outbreaks of IPN in farmed Atlantic salmon may cause a localized small increase in the prevalence of IPNV in wild marine fish.

Detection of infectious pancreatic necrosis virus (IPNV) from the environment in the vicinity of IPNV-infected Atlantic salmon farms in Scotland.

Infectious pancreatic necrosis virus (IPNV) has been isolated from mussels, sediment and surface water in the vicinity of clinically infected salmon farms, at shore bases supplying the farms and for several hundred metres distance from farms in the direction of current flow. There was evidence of decreasing prevalence of IPNV in mussels from Shetland once IPN outbreaks subsided, indicating they are an unlikely source of re-infection on farms. There was little evidence of persistence in the environment, although conclusions were complicated by the presence of IPNV on neighbouring farms 1 year after the outbreak.