The relationship between salmon (Salmo salar) farming and cell abundance of harmful algal taxa

The effects of nutrient effluents from fish cage aquaculture are an important eutrophication concern. It has been proposed that marine fish farm derived nutrients have the potential to increase phytoplankton abundance and lead to intensification of Harmful Algal Blooms (HABs), and that these blooms may negatively impact both the finfish and the shellfish industry. This study addressed this hypothesis using farmed salmon biomass in Scottish marine waters (as a proxy for nutrient load added to the water column as a consequence of fish farming) cell abundance of HAB taxa that most frequently impact shellfish farms and human health in the region (Dinophysis spp., Alexandrium spp. and Pseudo-nitzschia spp.), and cell abundance of one phytoplankton species of particular concern to the salmon farming industry (Karenia mikimotoi). Data from a 15-year weekly HAB monitoring programme and parallel national monitoring data relating to salmon farm stocking biomass were summarised in 5 km per 5 km aggregation boxes. Linear regression models were used to assess (i) inter-annual variation in cell abundance and total annual farmed salmon biomass; (ii) intra-annual (monthly) variation in harmful phytoplankton cell abundance and salmon biomass; (iii) a further analysis included seasonal effects within the intra-annual analysis. Farmed salmon biomass alone had a non-significant effect on cell abundance of any of the studied phytoplankton taxa. In contrast, a significant effect on cell abundance was found when using location, month or season as the predictive variable. Despite the non-significant impact of fish biomass on phytoplankton counts, the relationship varied seasonally, with a different response of Dinophysis spp. indicating a taxa specific interaction. A possible explanation for the lack of a significant relationship between farmed salmon and harmful phytoplankton cell abundance is that aquaculture farms are generally located in hydrodynamically energetic locations where recurrent flushing likely allows efficient dilution of nutrients. Overall, the analyses suggest that current levels of salmon farming activities do not markedly impact the abundance of routinely monitored biotoxin producing or fish killing phytoplankton taxa in Scottish waters.

Different antibiotic profiles in wild and farmed Chilean salmonids. Which is the main source for antibiotic in fish?

Fish from both aquaculture and wild capture are exposed to veterinary and medicinal antibiotics (ABs). This study explored the occurrence and probable source of 46 antibiotic residues in muscle of farmed salmon and wild trout from Chile. Results showed that at least one AB was detected in all studied samples. Diverse patterns were observed between farmed and wild specimens, with higher ABs concentrations in wild fish. Considering antimicrobial resistance, detected ABs corresponded to the categories B (Restrict), C (Caution) and D (Prudence) established by Antimicrobial Advice Ad Hoc Expert Group (European Medicines Agency). Multivariate statistic was used to verify differences between farmed and wild populations, looking for the probable source of ABs as well. Principal components analysis (PCA) revealed that ciprofloxacin, moxifloxacin, enrofloxacin, amoxicillin, penicillin G, oxolinic acid, sulfamethoxazole, trimethoprim and clarithromycin were associated with wild samples, collected during the cold season. Conversely, norfloxacin, sulfaquinoxaline, sulfadimethoxine, nitrofurantoin, nalidixic acid, penicillin V, doxycycline, flumequine, oxacillin, pipemidic acid and sulfamethizole were associated with wild samples collected during the warm season. All farmed salmon samples were associated with ofloxacin, tetracycline, cephalexin, erythromycin, azithromycin, roxithromycin, sulfabenzamide, sulfamethazine, sulfapyridine, sulfisomidin, and sulfaguanidine. In addition, linear discriminant analysis showed that the AB profile in wild fish differ from farmed ones. Most samples showed ABs levels below the EU regulatory limit for edible fish, except for sulfaquinoxaline in one sample. Additionally, nitrofurantoin (banned in EU) was detected in one aquaculture sample. The differences observed between farmed and wild fish raise questions on the probable source of ABs, either aquaculture or urban anthropic activities. Further research is necessary for linking the ABs profile in wild fish with the anthropic source. However, to our knowledge, this is the first report showing differences in the ABs profile between wild and aquaculture salmonids, which could have both environmental and health consequences.

Chilean salmon farming vulnerability to external stressors: The COVID 19 as a case to test and build resilience

This study addresses the risk and vulnerability of Chilean salmon production to hazards resulting from the COVID-19 pandemic threat, including limited access to farms, limited processing capacity and reduced market demand. The role of different management approaches in reducing risk and vulnerability is also explored. Results suggest that concession areas having the largest accumulated and current biomass have the highest risk, which is also transferred to the municipal level. The scenarios modelled with better management practices that reduce diseases were able to reduce risks by 30-40%. The largest risk reduction is achieved when production biomass is divided in a more equitable manner among concession areas, suggesting the need for strategic improvements in spatial planning of the activity in the marine environment according to ecosystem carrying capacity and better practices. Improving adaptation capacity can reduce vulnerability between 20% and 30% for municipalities; for example, providing local employment can be a win-win management measure under the COVID-19 threat because it reduces movement of people and facilitates handling and responses to emergencies. A larger footprint in local economies and employment can also improve social perception and acceptance of the sector, thus contributing to improve adaptation changes and governance to face the threats. The framework used here to perform a risk and vulnerability assessment of salmon farming to the pandemic-associated threats can also be useful for other aquaculture systems elsewhere, provided that relevant information is available.

Mycoremediation of oxytetracycline by marine fungi mycelium isolated from salmon farming areas in the south of Chile

Antibiotics are extensively used for growth promotion purposes in intensive aquaculture. In Chile, the use of antibiotics in salmon farming is excessive, approximately 62 times more than is used in Norway. In the salmon industry, antibiotics such as oxytetracycline (OTC) are administered in the diet, both in the juvenile stage in freshwater and in the fattening process of salmon in marine sectors. We have investigated the fjords of Chile, where many salmon farms are located, searching for fungi able to degrade this tetracycline antibiotic. We have evaluated the OTC degradation ability of the following; Penicillium commune, Epicoccum nigrum, Trichoderma harzianum, Aspergillus terreus and Beauveria bassiana, isolated from sediments in salmon farms from southern Chile. In all these fungal strains, the amount of OTC decreased in the culture medium, as adsorbed in the mycelia, after the third day of exposure. These strains were capable of degrading OTC at remarkable rates up to 78%, by the 15th day. This is the first study showing that the mycelium of these fungal strains has the ability to degrade OTC. We believe the knowledge produced by these results has the potential to serve as a basis for implementing a bioremediation process in the near future.

Genome-wide survey of cytochrome P450 genes in the salmon louse Lepeophtheirus salmonis (Krøyer, 1837)

Background

The salmon louse (Lepeophtheirus salmonis) infests farmed and wild salmonid fishes, causing considerable economic damage to the salmon farming industry. Infestations of farmed salmon are controlled using a combination of non-medicinal approaches and veterinary drug treatments. While L. salmonis has developed resistance to most available salmon delousing agents, relatively little is known about the molecular mechanisms involved. Members of the cytochrome P450 (CYP) superfamily are typically monooxygenases, some of which are involved in the biosynthesis and metabolism of endogenous compounds, while others have central roles in the detoxification of xenobiotics. In terrestrial arthropods, insecticide resistance can be based on the enhanced expression of CYPs. The reported research aimed to characterise the CYP superfamily in L. salmonis and assess its potential roles in drug resistance.

Methods

Lepeophtheirus salmonis CYPs were identified by homology searches of the genome and transcriptome of the parasite. CYP transcript abundance in drug susceptible and multi-resistant L. salmonis was assessed by quantitative reverse transcription PCR, taking into account both constitutive expression and expression in parasites exposed to sublethal levels of salmon delousing agents, ecdysteroids and environmental chemicals.

Results

The above strategy led to the identification of 25 CYP genes/pseudogenes in L. salmonis, making its CYP superfamily the most compact characterised for any arthropod to date. Lepeophtheirus salmonis possesses homologues of a number of arthropod CYP genes with roles in ecdysteroid metabolism, such as the fruit fly genes disembodied, shadow, shade, spook and Cyp18a1. CYP transcript expression did not differ between one drug susceptible and one multi-resistant strain of L. salmonis. Exposure of L. salmonis to emamectin benzoate or deltamethrin caused the transcriptional upregulation of certain CYPs. In contrast, neither ecdysteroid nor benzo[a]pyrene exposure affected CYP transcription significantly.

Conclusions

The parasite L. salmonis is demonstrated to possess the most compact CYP superfamily characterised for any arthropod to date. The complement of CYP genes in L. salmonis includes conserved CYP genes involved in ecdysteroid biosynthesis and metabolism, as well as drug-inducible CYP genes. The present study does not provide evidence for a role of CYP genes in the decreased susceptibility of the multiresistant parasite strain studied.

Effects of pharmaceuticals used to treat salmon lice on non-target species: Evidence from a systematic review

Aquaculture is currently one of the best prospects to help meet the growing need for protein in the human diet. However, aquaculture development and production result in consequences for the environment and also impact other productive activities. Salmon and trout cage culture has required the use of large quantities of pharmaceuticals in order to control outbreaks and the persistence of different pathogens, including sea lice (parasitic copepods), which cause economic losses of around 0.39 € Kg^-1 of salmon produced. The pharmaceuticals currently used for the control of sea lice (cypermethrin, deltamethrin, azamethiphos, hydrogen peroxide) are applied by in situ immersion treatments, enclosing net pens using tarpaulin and then bathing fish with the pharmaceutical. After treatment the pharmaceuticals are released into the surrounding environment, exposing non-target species. Although the effects of such pharmaceutical exposure has been studied in some species, to date a systematic and exhaustive review of these potential effects has not yet been performed. In this study, an exhaustive review of the literature evaluating lethal and sub-lethal effects of anti-sea lice pharmaceuticals on non-target crustaceans and bivalves was performed, in order to assess the extent of the effects, toxicity, variables affecting such toxicity and identify potential synergistic effects previously unexplored. Our results show clear negative effects at concentrations lower than those used in treatments against sea lice in all of the species studied. Likewise, this study demonstrates knowledge gaps that need to be addressed in order to improve our understanding of the effects of these pharmaceuticals on non-target species, ecosystems in general and other productive activities.

Exposure to teflubenzuron negatively impacts exploratory behavior, learning and activity of juvenile European lobster (Homarus gammarus)

Infestations with salmon lice, a parasitic copepod, is a major problem in the salmon farming industry. Teflubenzuron is an in-feed pharmaceutical applied to control lice outbreaks; the standard medication is 10 mg per kg fish per day for seven days. Surveys reveal that teflubenzuron accumulates and persists in the sediment around fish farms and causes deformities and mortality in juvenile European lobster (Homarus gammarus), a species commonly found in the vicinity of salmon farms in Norway. To date, there is no information on sub-lethal effects of teflubenzuron on, for example, behavior. We conducted an experiment to assess possible difference in the shelter seeking behavior of teflubenzuron-exposed (N = 19) vs. not exposed (N = 19) H. gammarus juveniles. The teflubenzuron-exposed juveniles had been given very low concentrations, 1.7 µg per pellet twice per week for 113 days prior to this experiment. The concentration of teflubenzuron was estimated to be less than 1 ng/g lobster when they were tested in the behavior experiment. Animals were placed in a lane with a shelter at one end. Once a lobster had found and entered the shelter, they were repeatedly displaced back to the opposite end of the lane, for a total of 3 repeated runs per animal. Three of the exposed juveniles failed to settle in the shelter, and the remaining teflubenzuron-exposed animals took significantly more time to explore the environment and to find and recognize shelter. Furthermore, exposed lobsters also exhibited slower walking speed compared to the controls. These results demonstrate that teflubenzuron significantly reduces exploratory behavior, learning and activity of juvenile H. gammarus. Thus, exposure to teflubenzuron could increase predation mortality of juvenile lobsters in the wild.

Photosynthesis and nitrogen uptake of the giant kelp Macrocystis pyrifera (Ochrophyta) grown close to salmon farms

Finfish aquaculture is an activity that has experienced an explosive global development, but presents several environmental risks, such as high nitrogen outputs with potential eutrophication consequences. Therefore, the integration of seaweed aquaculture with the aim of decreasing nitrogen emissions associated with intensive salmon farming has been proposed as a bioremediation solution. Ecophysiological knowledge about seaweeds cultured close to farming cages is, however, still rudimentary. We experimentally studied the growth and physiological responses of Macrocystis pyrifera (Linnaeus) C. Agardh in a suspended culture system near a commercial salmon farm at three culture depths in order to understand its productivity performance. The results showed maximum growth responses at intermediate depths (3 m) as opposed to near the surface (1 m) or at a deeper culture level (6 m). At 6 m depth, light limitations were detected, whereas the sporophytes growing at 1 m depth responded to high irradiances, especially in late spring and summer, where they were more intensely exposed to decay of photosynthesis than individuals from other depths. Accordingly, photosynthetic pigment concentrations (chlorophyll a and c, and fucoxonthin) were higher during low-light seasons (winter and early spring) but decreased during the summer. On the other hand, although both nitrogen uptake and Nitrate Reductase (NR) activity varied seasonally, increasing significantly in spring and summer, these variables were not affected by culture depth. Therefore, the optimal culture depth of M. pyrifera near salmon farms appears to be a physiological integration between nitrogen supply and demand, which is modulated by plant acclimation to the seasonal change in light and temperature. The results allow to discuss about the environmental constrains of M. pyrifera in an ecophysiological context to improve the understanding of its aquaculture, and to contribute relevant information on the use of this species in bioremediation.

Occurrence and Distribution of Deltamethrin and Diflubenzuron in Surface Sediments from the Reloncaví Fjord and the Chiloé Inner-Sea (~ 39.5ºS -43ºS), Chilean Patagonia

Surface sediments from Reloncaví Fjord and the Chiloé inner sea in Chilean Patagonia were extracted and analyzed to estimate deltamethrin and diflubenzuron levels. These antiparasitary pesticides have been used for decades in the salmon industry. Relationships were determined between pesticide concentrations and organic carbon percent in sediments. Deltamethrin (0.39-1.05 µg g^-1 dw) was found at all sampling sites but diflubenzuron (0.06-0.09 µg g^-1 dw) at only five. Diflubenzuron levels were similar for sediments from other fjord areas. However, deltamethrin concentration was 2-3 fold higher than other studies on this area. The organic carbon percent was correlated positively and significantly with diflubenzuron, but not with deltamethrin. Our results suggest that the high deltamethrin concentrations in sediments are due to the increased use of pyrethroids around salmon farming areas. But, the diflubenzuron levels can be explained by degradation processes.

Temporal variation on environmental variables and pollution indicators in marine sediments under sea Salmon farming cages in protected and exposed zones in the Chilean inland Southern Sea

The impacts of any activity on marine ecosystems will depend on the characteristics of the receptor medium and its resilience to external pressures. Salmon farming industry develops along a constant gradient of hydrodynamic conditions in the south of Chile. However, the influence of the hydrodynamic characteristics (weak or strong) on the impacts of intensive salmon farming is still poorly understood. This one year study evaluates the impacts of salmon farming on the marine sediments of both protected and exposed marine zones differing in their hydrodynamic characteristics. Six physico-chemical, five biological variables and seven indexes of marine sediments status were evaluated under the salmon farming cages and control sites. Our results identified a few key variables and indexes necessary to accurately evaluate the salmon farming impacts on both protected and exposed zones. Interestingly, the ranking of importance of the variables and the temporality of the observed changes, varied depending on the hydrodynamic characteristics. Biological variables (nematodes abundance) and environmental indexes (Simpson's dominance, Shannon's diversity and Pielou evenness) are the first to reflect detrimental impacts under the salmon farming cages. Then the physico-chemical variables such as redox, sulphurs and phosphorus in both zones also show detrimental impacts. Based on the present results we propose that the hydrodynamic regime is an important driver of the magnitude and temporality of the effects of salmon farming on marine sediments. The variables and indexes that best reflect the effects of salmon farming, in both protected and exposed zones, are also described.

Tenacibaculum finnmarkense sp. nov., a fish pathogenic bacterium of the family Flavobacteriaceae isolated from Atlantic salmon

A novel Gram-stain negative, aerobic, non-flagellated, rod-shaped gliding bacterial strain, designated HFJ(T), was isolated from a skin lesion of a diseased Atlantic salmon (Salmo salar L.) in Finnmark, Norway. Colonies were observed to be yellow pigmented with entire and/or undulating margins and did not adhere to the agar. The 16S rRNA gene sequence showed that the strain belongs to the genus Tenacibaculum (family Flavobacteriaceae, phylum 'Bacteroidetes'). Strain HFJ(T) exhibits high 16S rRNA gene sequence similarity values to Tenacibaculum dicentrarchi NCIMB 14598(T) (97.2 %). The strain was found to grow at 2-20 °C and only in the presence of sea salts. The respiratory quinone was identified as menaquinone 6 and the major fatty acids were identified as summed feature 3 (comprising C16:1 ω7c and/or iso-C15:0 2-OH), iso-C15:0, anteiso-C15:0, iso-C15:1 and iso-C15:0 3-OH. The DNA G+C content was determined to be 34.1 mol%. DNA-DNA hybridization and comparative phenotypic and genetic tests were performed with the phylogenetically closely related type strains, T. dicentrarchi NCIMB 14598(T) and Tenacibaculum ovolyticum NCIMB 13127(T). These data, as well as phylogenetic analyses, suggest that strain HFJ(T) should be classified as a representative of a novel species in the genus Tenacibaculum, for which the name Tenacibaculum finnmarkense sp. nov. is proposed; the type strain is HFJ (T) = (DSM 28541(T) = NCIMB 42386(T)).

Effects of aquaculture fallowing on the recovery of macrofauna communities

The fallowing period is a management measure in aquaculture where the production is paused for a few months to reduce the impact on the benthic environment. We studied the effects of different fallowing periods on the recovery of macrofauna at two salmon farms in Norway. The macrofauna at the farm stations were characterised by high abundances of opportunistic taxa (e.g. Capitella spp.), low diversity and significantly different community structure compared to reference sites. The fallowing initiated macrofauna recovery at both farm stations, indicated by a decline of dominant opportunistic taxa after 2months. Significant changes in taxa composition occurred only after 6months, although indications of disturbance were still evident. Surprisingly, no corresponding spatial or temporal differences were found in the sediment parameters such as redox, TOC and pH. The results suggest that macrofauna is a more sensitive indicator and that the seasonal timing of fallowing may affect recovery dynamics.

The combined impact of land use change and aquaculture on sediment and water quality in oligotrophic Lake Rupanco (North Patagonia, Chile, 40.8°S)

Water and sediment quality in North Patagonia's large, oligotrophic lakes are expected to suffer as native forest continues to be fragmented and degraded by its conversion to cropping and pasture land uses. These changes in land use are expected to increase diffuse nutrient loads to the region's lakes. In addition, these lakes are home to the world's second largest salmon aquaculture industry which provides additional point sources of nutrients within the lakes. We studied the combined influences of land use change and salmon farming on the nutrient concentrations in a North Patagonian lake (Lake Rupanco, 233 km(2) water surface, 163 m average depth) in four sub-watersheds ranging in disturbance from near-pristine forest to 53% converted to cropping and pasture. Nitrogen exports from the tributary sub-watersheds increased from 33 kg TN/km(2)/y to 621 kg TN/km(2)/y as the proportion of crop and pasture land increased. The combined nutrient load from land use change and salmon farming has led to significant differences in the nitrogen concentrations of the lake's water column and sediments in the near-shore zones across the lake. Total nitrogen concentrations in the sediments varied from 37 ± 18 mg/kg in near-pristine sub-watersheds without salmon farming to 6400 ± 698 mg/kg where the sub-watershed was dominated by crop and pasture lands combined with the presence of salmon farming. These results demonstrate the importance of considering the impacts of both salmon farming and land use on water and sediment quality for future environmental planning, management and decision making.