Showing papers in "Aquaculture Environment Interactions in 2020"

Sea lice removal by cleaner fish in salmon aquaculture: a review of the evidence base

Abstract: Stocking cleaner fish to control sea lice infestations in Atlantic salmon farms is widespread and is viewed as a salmon welfare-friendly alternative to current delousing control treatments. The escalating demand for cleaner fish (~60 million stocked worldwide per year), coupled with evidence that they experience poor welfare and high mortality in sea cages, requires that the lice removal effect of cleaner fish be substantiated by robust evidence. Here, we systematically ana lysed (1) studies that tested the delousing efficacy of cleaner fish species in tanks or sea cages and (2) studies of spatial overlap — and therefore likely encounter rate — between cleaner fish and salmon when stocked together in sea cages. Only 11 studies compared lice removal between tanks or cages with and without cleaner fish using a replicated experimental design. Most studies had insufficient replication (1 or 2 replicates) and were conducted in small-scale tanks or cages, which does not reflect the large volume and deep cages in which they are deployed commercially. Reported efficacies varied across species and experimental scale: from a 28% increase to a 100% reduction in lice numbers when cleaner fish were used. Further, our review revealed that the interaction of cleaner fish and salmon in sea cages has rarely been documented. While much of the evidence is promising, there is a mismatch between the current evidence and the extent of use by the industry. We recommend replicated studies in 9 key areas at a full commercial scale across all species that are currently widely used. More targeted, evidence-based use of cleaner fish should increase their efficacy and help to alleviate economic, environmental, and ethical concerns.

Sea lice prevention strategies affect cleaner fish delousing efficacy in commercial Atlantic salmon sea cages

Abstract: Over the last 2 decades, cleaner fishes have been employed to remove external sea lice parasites from Atlantic salmon Salmo salar in sea cages. Norway, Scotland, Ireland, and the Faroe Islands combined now use ~60 million cleaner fish per year. While small-scale experiments demonstrate the efficacy of cleaner fishes, industrial-scale sea cages have multiple structures and conditions that create different environments, which may impact cleaner fish efficacy and welfare. Here, in commercial sea cages, we investigated if 4 different anti-lice strategies impacted the delousing efficacy, physical condition, and behaviour of cleaner fish (corkwing wrasse Symphodus melops). The strategies tested were: (1) cleaner fishes only; (2) cleaner fishes and functional feed; (3) cleaner fishes, functional feed, and deep lights and feeding; and (4) cleaner fishes, functional feed, deep lights and feeding, and lice skirts. Corkwing wrasse were sampled from 3 cage-level replicates of each anti-lice strategy 3 times over 2 mo. Lice levels on salmon were recorded every 3 to 4 wk. Only 11% of corkwing wrasse had salmon lice in their gut, with individual wrasse having up to 72 lice in their stomach. Wrasse in cages encircled by lice skirts consumed one-ninth as many lice as those in other anti-lice treatments and had less overall impact on the number of lice per salmon. Fin, skin, mouth and eye condition, K factor, and observed cleaning behaviours of corkwing wrasse were similar across all anti-lice strategies. Our results demonstrate that different in-cage anti-lice strategies altered the magnitude of lice consumption in corkwing wrasse at this site and for this production period. Moreover, while a small proportion of corkwing wrasse appear to target lice as prey, most individual corkwing wrasse were ineffective biological control agents in a full-scale farm setting.

Spill-over from aquaculture may provide a larval subsidy for the restoration of mussel reefs

Abstract: Worldwide bivalve aquaculture is expanding rapidly. Simultaneously, there has been a loss of natural bivalve reefs due to anthropogenic activities. As bivalve reefs support several ecosystem functions disproportionate to the area they cover, there is interest in their restoration. The Firth of Thames (FoT) in northern New Zealand once supported dense populations of green lipped musselsPerna canaliculus, which were extirpated by a dredge fishery in the mid-20thcentury. Efforts to restore these biogenic habitats are underway. The largest standing populations of this species in the area currently exist in aquaculture. This study aimed to determine if larval spill-over from aquaculture can provide a larval subsidy to bivalve reef restoration efforts in the FoT. We used a combination of trace elemental fingerprinting and biophysical modelling techniques to determine patterns of larval dispersal in the area. Results of both approaches indicated that the larval pool in the area is well mixed with larvae produced at aquaculture locations capable of settling throughout the study area. Overall this shows, for the first time, that larval spill-over from aquaculture may provide a subsidy to restoration efforts and assist with establishing sustainable populations. When determining restoration locations, the potential for aquaculture populations to act as a larval source should be explicitly considered. Conversely, when considering the location of new aquaculture sites, the consequences of larval spill-over to surrounding wild populations should be assessed. We recommend that restoration efforts and aquaculture be carefully integrated in a network approach which could provide both ecological and economic benefits.

Decay of peracetic acid in seawater and implications for its chemotherapeutic potential in aquaculture

Abstract: Peracetic acid (PAA) is a widely applied disinfectant in aquaculture. Knowledge on PAA decay in seawater (SW) is crucial for its successful implementation in SW aquaculture systems. We investigated the decay dynamics of PAA in SW under controlled conditions to assess the potential effect of temperature, salinity and light. We also applied PAA to 22 tanks with post-smolt Atlantic salmonSalmo salarin full-strength SW (33‰) over a realistic range of therapeutic concentrations (0.15-4.8 mg l-1) to simulate relevant treatment scenarios. The study showed that PAA degrades rapidly in SW. The degradation follows exponential first-order decay with half-lives on the order of minutes to hours. Salinity and temperature significantly affected the decay of PAA, showing a 4-fold faster decay rate in full-strength SW compared to freshwater. The decay of PAA was not significantly related to the nominal concentration of PAA in the concentration range tested. The other 2 active ingredients in PAA products, hydrogen peroxide (H2O2) and acetic acid, were found to degrade at a much slower rate. H2O2half-lives in SW were found to range from 15 to 70 h, and minimal acetate was found to be degraded when added to SW. Finally, we compiled published data on PAA decay in relevant water matrices and discussed the potential environmental impacts, mitigation options and future research.

Biological controls to manage Acropora-eating flatworms in coral aquaculture

Abstract: Coral aquaculture is expanding to supply the marine ornamental trade and active coral reef restoration. A common pest of Acropora corals is the Acropora-eating flatworm Prosthiostomum acroporae, which can cause colonial mortality at high infestation densities on Acropora spp. We investigated the potential of 2 biological control organisms in marine aquaria for the control of P. acroporae infestations. A. millepora fragments infested with adult polyclad flatworms (5 flatworms fragment(-1)) or single egg clusters laid on Acropora skeleton were cohabited with either sixline wrasse Pseudocheilinus hexataenia or the peppermint shrimp Lysmata vittata and compared to a control (i.e. no predator) to assess their ability to consume P. acroporae at different life stages over 24 h. P. hexataenia consumed 100% of adult flatworms from A. millepora fragments (n = 9; 5 flatworms fragment(-1)), while L. vittata consumed 82.0 +/- 26.36% of adult flatworms (mean +/- SD; n= 20). Pseudocheilinus hexataenia did not consume any Prosthiostomum acroporae egg capsules, while L. vittata consumed 63.67 +/- 43.48% (n = 20) of egg capsules on the Acropora skeletons. Mean handling losses in controls were 5.83% (shrimp system) and 3.50% (fish system) of flatworms and 2.39% (fish system) and 3.50% (shrimp system) of egg capsules. Encounters between L. vittata and P. hexataenia result in predation of P. acroporae on an Acropora coral host and represent viable biological controls for reducing infestations of P. acroporae in aquaculture systems.

European lobsters utilise Atlantic salmon wastes in coastal integrated multi-trophic aquaculture systems

Abstract: In this study, we investigated if juvenile European lobsters Homarus gammarus would eat waste from Atlantic salmon Salmo salar cages in a coastal integrated multi-trophic aquaculture (IMTA) setup and if there were any impacts on growth. Trophic interactions between salmon and lobsters were assessed using δ15N and δ13C stable isotope analysis and fatty acid profiling from fish feed as indicators of nutrient flow. Analysis revealed that lobsters directly utilised particulate waste from salmon production, as levels of indicator fatty acids from salmon feed were significantly higher in lobster tissues near the fish cages compared to the control site. Route of uptake may have been direct consumption of waste feed or faecal material or indirectly through fouling organisms. Stable isotope analysis did not indicate nutrient transfer to lobsters, suggesting that the duration of the study and/or the amount of waste consumed was not sufficient for stable isotope analysis. Lobsters grew significantly over the trial period at both sites, but there was no significant difference in lobster growth between the sites. Our results show a trophic relationship between salmon and lobsters within this IMTA system, with no apparent advantage or disadvantage to growth.

Growth, health and biochemical composition of the sea cucumber Cucumaria frondosa after multi-year holding in effluent waters of land-based salmon culture

Abstract: Methods have been proposed to mitigate the environmental footprint of aquaculture, including co-culture of species occupying different trophic levels. In this study, sea cucumbers Cucumaria frondosa, either from production tanks fed with effluent water from land-based salmon culture over 4 yr or collected from the field, were compared using stable isotope, lipid and fatty acid (FA) signatures as indicators of waste assimilation, health and biochemical composition. Enrichment of δ13C in muscle bands and intestine and of δ15N in muscle bands, gonad and intestine was detected in captive individuals relative to wild individuals, suggesting the uptake and assimilation of waste from salmon culture. The higher levels of FA biomarkers typical of salmon feed (18:1ω9, 18:2ω6 and 20:1ω9) and lower ω3/ω6 ratio in the captive sea cucumbers were also in line with assimilation of the waste. However, male and female sea cucumbers from the co-culture became smaller with time, their organ indices were lower than those of wild individuals (e.g. poorly developed gonad), and their biochemical composition differed: triacylglycerol content was greater in wild individuals and phospholipid content was greater in captive individuals. Also, FA profiles of all tissues differed between the 2 groups, whereas total lipid in muscle bands and gonad remained similar. Overall, results support that co-culture with suspension-feeding sea cucumbers may help mitigate the salmon industry footprint. In turn, the biochemical composition of the sea cucumbers changed, and their reduced size and body indices suggest that this food source does not provide suitable nutrients to sustain growth and reproduction.

Functional role of biofouling linked to aquaculture facilities in Mediterranean enclosed locations

Abstract: Biofouling is generally considered a serious threat for human coastal activities such as aquaculture, and the ecological role of fouling organisms associated with fish-farm cages re mains one of the most debated topics in the ecological field. However, although biofouling may cause significant problems related to human health, environmental impact and financial losses, in the past decade there has been an increasing interest in developing methods to promote the growth of biofouling on artificial structures as a strategy to mitigate human impacts and reduce the organic enrichment caused by net-cage fish farming. Here we investigated the filtration activity of biofouling assemblages colonizing artificial substrata located within a harbor. The main objective of the study was to determine if and how changes in composition and functioning of biofouling may be affected by hypoxic conditions that periodically occur within the port site selected for this study. To this purpose, artificial panels were used as biofouling collectors and were brought back to the laboratory seasonally where they were divided in 3 subgroups and acclimated at 3 different oxygen levels to mimic the naturally occurring oxygenic conditions. Clearance and respiration rates of each community were measured 6 and 24 h after the beginning of each treatment. Regardless of experimental conditions, performance of the communities was affected by the seasonality and the amount of biomass recruiting on the panels, mainly composed of crustaceans, ascidians, polychaetes, seaweeds and several introduced species. Our study demonstrated that, in particular cases, fouling assemblages linked to aquaculture facilities may contribute to reducing environmental impact and at the same time may serve as input for their re-use in different disciplines.

Site selection of mussel mitigation cultures in relation to efficient nutrient compensation of fish farming

Abstract: In the Baltic Sea, rainbow trout Oncorhynchus mykiss is the most common species used in marine aquaculture, but further increase in production is problematic due to environmental legal regulations, especially in the coastal zone. A solution could be to place the fish farms offshore and use mussel mitigation cultures to extract nutrients released from the fish farms. We used 3D ecological modeling to identify suitable locations for mussel mitigation cultures in relation to nutrient pollution from a fish farm in the inner Danish waters. The model results showed that potential mussel harvest depended on the food flux following a saturation curve with a maximum yield of 2100 to 2600 t wet weight and then stabilized at around 2100 to 2600 t wet weight of mussels. A single mussel farm (36 ha) can potentially remove 17-31% of the released nitrogen from the fish farm. Mussel farms located inside or a few km outside the coastal areas receiving the highest nutrient inputs from the fish farm were found to be the most suitable among the tested sites. In contrast, co-location with the fish farm was not advisable due to the negative benthic impact below the farms. However, it is up to the managers to decide which positive and negative effects should receive the most attention, given the present need for protection of water bodies and habitats and in relation to other activities in the area. This study demonstrates that modeling can support management decisions with respect to site selection of aquaculture and provide the needed data on far-field and local environmental effects from integrated aquaculture.

Impact of variable physical conditions and future increased aquaculture production on lice infestation pressure and its sustainability in Norway

Abstract: Salmon lice infestation is a challenge for wild post-smolt salmon during migration from their natal river to the sea in several regions of Norway. The traffic-light management system regulates growth in the aquaculture industry, where growth in production (6%) is only allowed if the impact of salmon lice on wild fish can be kept at a minimum and up to 10% mortality of wild salmonids are considered within the sustainability goal. We used a numerical ocean model, combined with an individual-based model for salmon lice, to evaluate the interannual variability in salmon lice concentrations in Production Zone 7, which was granted permission for production growth in 2017. Salmon lice releases were kept constant for 3 yr, while the physical conditions, e.g. wind and ocean circulation, varied. The total area of elevated lice infestations varied between 3.2 and 8.4% of the area within 5 km from the coast, due only to interannual physical variability mainly caused by variable wind patterns. Modeled post-smolts migrating out from the Namsen River (64.5°N, central Norway) towards the open ocean experienced mortality between 5 and 9%. Since Production Zone 7 was granted growth, we have simulated increased production and corresponding increases in lice releases. After 5 to 8 increments of 6% increase in production, the increase in salmon post-smolt mortality was of the same order of magnitude as the interannual variability. Information regarding migration route and time is crucial input to the model calculating post-smolt mortality, and inadequate information can affect the results significantly. These 2 methods (determining area of elevated lice infestations and estimating post-smolt mortality) provide complementary information and should be used in combination when the overall assessment of a production zone is made.

Impact of thermoclines on the vertical distribution of salmon lice larvae

Abstract: Salmon louse Lepeophtheirus salmonis, a key parasite of salmonids, is managed by multiple methods at both salmon farmand ecosystem-scale that are informed by an understanding of the abundance and distribution of the infective, planktonic stage of the lice. Dispersal modelling using hydrodynamic models relies on accurately estimating larval depth and how environmental variables modify distributions. Larval responses to temperature could modify dispersal distances by altering their depth in the water column and thus exposure to depth-dependent oceanographic processes and the duration of their temperature-dependent development. Using column experiments, we tested how L. salmonis nauplii and copepodids responded to different thermoclines by establishing a bottom layer of 12°C with an overlaying layer varying from 6 to 18°C in 2°C steps. Nauplii moved upwards in high proportions and aggregated in the surface layer when the overlying layer was 10°C or cooler. In contrast, nauplii moved downwards and aggregated at the thermocline when the overlying layer exceeded 12°C. Temperature did not influence the vertical distribution of copepodids. When nauplii behaviour towards temperature was integrated into a dispersal model, dispersal distances increased. Temperature should be considered when calculating depth distributions. Further, nauplii and copepodids behave differently and should be configured separately in dispersal models.

Hydrodynamic connectivity, water temperature, and salinity are major drivers of piscirickettsiosis prevalence and transmission among salmonid farms in Chile

Abstract: Piscirickettsiosis is one of the most im portant diseases affecting farmed salmonid in Chile. Several studies have demonstrated the survival of Piscirickettsia salmonis in seawater and the horizontal transmission from infected to non-infected fish; however, the extent of waterborne transmission between farms has not been quantified. In this study, we used a stochastic hydrodynamic connectivity-based disease spread model to determine the role of hydrodynamic connectivity and the effect of seawater temperature and salinity on the dynamics of piscirickettsiosis in the Los Lagos region of Chile. Results demonstrate that environmental dynamics play a major role in disease prevalence.Thestrongestdeterminantsofpiscirickettsiosis prevalence were the number of infected farms in upstream watersand theextentofdiseaseoutbreaksin upstreamwaters(totalmortality), followedbyseawater salinity and temperature. In farms downstream from infected farms, observed disease prevalence 25 wk into the farming cycle was close to 100%, while in farms with little or no exposure to upstream, infected farms, prevalence reached only ~10% by the end of the farming cycle (Week 56). No previous studies have quantified the scales of connectivity associated with piscirickettsiosis or provided risk metrics of waterborne transmission of the disease among farms; these are a novel aspect of this research. The above knowledge regarding the use of the epidemiological model will allow industry and regulators to better target disease control strategies for more effective control of piscirickettsiosis in the study area.

Artificial habitat and biofouling species distributions in an aquaculture seascape

Abstract: The global proliferation of marine artificial habitats is rapidly altering the physical structure of coastlines, with knock-on effects on physical, chemical, and ecological processes at seascape scales. Ecological consequences of maritime sprawl associated with aquaculture are poorly understood, despite the fact that these suspended structures are particularly prone to biofouling, which can affect the industry and seascape around it. We characterised seascape-scale spatial and temporal distribution patterns of 10 biofouling taxa in relation to the presence and distance to Perna canaliculus mussel farms in New Zealand’s largest aquaculture region. Seven of 10 taxa had significantly higher cover on farms than in natural habitats throughout the region. The cover of 4 of those 7 taxa, including the high-profile pests Mytilus galloprovincialis and Undaria pinnatifida, exponentially decreased with distance from the nearest farm, while some taxa were absent from natural habitats (e.g. the ascidian Ciona robusta). In contrast, several opportunistic macroalgal species, such as Cladophora ruchingeri and Pylaiella littoralis, had colonised extensive areas of natural habitat. Our results suggest that biofouling is a persistent issue on mussel farms and that farm structures may act as reservoirs or ‘stepping stones’ for the dispersal of potential marine pests. These distributional and dispersal patterns can inform integrated pest management efforts focusing on spatial management strategies, such as ‘firebreaks’ in farm connectivity, avoidance of pest hotspots, and farm fallowing.

Integrated multi-trophic aquaculture systems: energy transfers and food web organization in coastal earthen ponds

Abstract: Three Ecopath models were built to reproduce 3 experimental treatments carried out in earthen ponds located in Olhão, southern Portugal, to understand the energy transferred and the ecosystem state in integrated multi-trophic aquaculture (IMTA). These earthen ponds behave as simplified ecosystems or mesocosms, with well-defined borders, where the relationships between trophic groups can be described through ecosystem modeling. Different combinations of species were produced in these ponds, corresponding to the 3 treatments: (1) fish, oysters and macroalgae (FOM); (2) fish and oysters (FO); and (3) fish and macroalgae (FM). The managed species were meagre Argyrosomus regius, white seabream Diplodus sargus, flathead grey mullet Mugil cephalus, Japanese oyster Crassostrea gigas and sea lettuce Ulva spp. The results showed that the total amount of energy throughput was 15 to 17 times higher when compared with an equivalent naturalized system. The high biomass and low recycling indicated an immature system with low resilience and low stability that demands high rates of water renewal and aeration to maintain good water-quality levels for finfish production. The addition of oysters and macroalgae in the FOM treatment appeared to improve the water quality, since oysters controlled the excess of phytoplankton produced in the ponds by ingesting a fair amount of the phytoplankton, while the macroalgae helped in the absorption of excess nutrients and created a habitat for periphyton and associated macroinvertebrates. Some ecosystem attributes of the FOM ponds approached the values of the naturalized model, suggesting a possible path towards more sustainable aquaculture.

Beyond hybridization: the genetic impacts of non-reproductive ecological interactions of salmon aquaculture on wild populations

Abstract: Cultured Atlantic salmon Salmo salar are of international socioeconomic value, and the process of domestication has resulted in significant behavioural, morphological, and allelic differences from wild populations. Substantial evidence indicates that direct genetic interactions or interbreeding between wild and escaped farmed Atlantic salmon occurs, genetically altering wild salmon and reducing population viability. However, genetic interactions may also occur through ecological mechanisms (e.g. disease, parasites, predation, competition), both in conjunction with and in the absence of interbreeding. Here we examine existing evidence for ecological and non-reproductive genetic interactions between domestic Atlantic salmon and wild populations and the potential use of genetic and genomic tools to resolve these impacts. Our review identified examples of genetic changes resulting from ecological processes, predominately through pathogen or parasite transmission. In addition, many examples were identified where aquaculture activities have either altered the selective landscape experienced by wild populations or resulted in reductions in population abundance, both of which are consistent with the widespread occurrence of indirect genetic changes. We further identify opportunities for genetic or genomic methods to quantify these impacts, though careful experimental design and pre-impact comparisons are often needed to accurately attribute genetic change to aquaculture activities. Our review indicates that ecological and non-reproductive genetic interactions are important, and further study is urgently needed to support an integrated understanding of aquaculture-ecosystem interactions, their implications for ecosystem stability, and the development of potential mitigation and management strategies.

Effect of substrate type and pellet age on the resuspension of Atlantic salmon faecal material

Abstract: The influence of substrate type and particle age on the remobilization of settled Atlantic salmon Salmo salar faecal material was studied through a set of controlled experiments in horizontal flow flumes, simulating different bottom conditions present in fish-farming locations along the coast of Norway. There was no significant effect of pellet age on remobilization for up to 1 week old faecal material, but critical shear stresses (τc) and velocities required for resuspending faecal pellets were strongly dependent on substrate type. Smooth substrates such as mud and rock slate required lower stresses for the onset of faeces resuspension (τc ≈ 0.06 Pa) than rougher surfaces such as sand (τc ≈ 0.12 Pa) or fragmented rock (τc ≈ 0.32 Pa), where bedforms and large fractures shield the particles from the direct influence of the drag forces. These newly determined substrate-dependent τc resuspension thresholds will contribute to the construction of more accurate numerical models that include bottom type as a parameter regulating the extent of particle spreading, in contrast to the constant-value approach that has been used to date.

Parameterising resuspension in aquaculture waste deposition modelling

Abstract: Sustainable expansion of global aquaculture depends on a thorough understanding of environmental impacts. Open-water culture operations produce waste food and faeces, the benthic impacts of which are a focus of regulation. Seabed interactions of wastes are complex, depending on current velocity, seabed substrate and waste material characteristics. The accuracy achieved in modelling intensity and spatial extent of impacts is contingent upon the representation of this interaction and its implications for resuspension. We used benthic flumes to study re suspension processes at 11 salmon aquaculture sites, covering a range of sediment types. Erosion rates and critical entrainment stress were computed at the cage edge and between 100 and 500 m away, characterising seabed erodibility in highly impacted and less impacted sediments. Heavily impacted cage-edge sediments had an erosion threshold (mean 0.02 N m−2) that was an order of magnitude lower, and markedly less heterogeneous, than that of nearby less impacted sediments (mean across sites 0.19 N m−2). This likely reflects a seabed which was smothered by waste material close to the depositional centre. Further out, the covering of waste material is less continuous, thinner, and more admixed with underlying sediments. Bed erosion rates were found to be a linear function of excess stress. The results provide important information on how benthic flumes can be deployed to collect spatial and temporal data for parameterisation of erosion and entrainment processes in numerical waste transport simulation models such as DEPOMOD, and the comparatively large field-based dataset should contribute to the goal of allowing a more realistic representation of particulate waste in these models.

Biochar-immobilized Sphingomonas sp. and Acinetobacter sp. isolates to enhance nutrient removal: potential application in crab aquaculture

Abstract: The frequency of water exchange and reducing the risk of eutrophication to surrounding water bodies have always been water-quality control issues in recirculating aquaculture systems. In this study, maize straw biochar prepared through pyrolysis showed great potential for both bacterial immobilization and pollutant adsorption. Heterotrophic bacterial strains of Sphingomonas sp. PDD-57b-25 and Acinetobacter towneri were isolated in situ from wastewater for pollutant remediation through a 16S rDNA-based method, which has been rarely reported to date. The selected strains had higher ammonia nitrogen (NH4+-N, 63%), nitrite nitrogen (NO2--N, 38%), nitrate nitrogen (NO3--N, 25%) and total phosphorus (TP, 35%) assimilation capacities than those of other widely applied bacteria under similar medium conditions. In addition, more NH4+-N (+16%), NO2--N (+14%), NO3--N (+17%) and TP (+19%) was removed by biochar-immobilized isolated strains than dissociated strains, suggesting their use may provide a means of improving water-quality control in recirculating aquaculture. With specific additions (4 g l-1) of biochar-immobilized Sphingomonas sp. PDD-57b-25 and A. towneri, the dissolved inorganic nitrogen (approximately 0.45 mg l-1) and TP (approximately 0.09 mg l-1) levels were maintained below the clean water threshold for recirculating aquaculture of crab Eriocheir sinensis. Furthermore, the added strains exhibited high bio-safety and were capable of improving the yield and quality of crabs. Results indicate the potential applicability of biochar-immobilized Sphingomonas sp. PDD-57b-25 and A. towneri in agricultural sewage treatments. Further, the experimental methodology developed here may be used for the exploration of new strains for practical aquaculture.

Model-based evaluation of the genetic impacts of farm-escaped Atlantic salmon on wild populations

Abstract: Genetic interactions (i.e. hybridization) between wild and escaped Atlantic salmon Salmo salar from aquaculture operations have been widely documented, yet the ability to incorporate predictions of risk into aquaculture siting advice has been limited. Here we demonstrate a model-based approach to assessing these potential genetic interactions using a salmon aquaculture expansion scenario in southern Newfoundland as an example. We use an eco-genetic individualbased Atlantic salmon model (IBSEM) parameterized for southern Newfoundland populations, with regional environmental data and field-based estimates of survival, to explore how the proportion of escapees relative to the size of wild populations could potentially influence genetic and demographic changes in wild populations. Our simulations suggest that both demographic decline and genetic change are predicted when the percentage of escapees in a river relative to wild population size is equal to or exceeds 10% annually. The occurrence of escapees in southern Newfoundland rivers under a proposed expansion scenario was predicted using river and site locations and models of dispersal for early and late escapees. Model predictions of escapee dispersal suggest that under the proposed expansion scenario, the number of escapees is expected to increase by 49% and the highest escapee concentrations will shift westward, consistent with the location of proposed expansion (20 rivers total >10% escapees, max 24%). Our results identify susceptible rivers and potential impacts predicted under the proposed aquaculture expansion scenario and illustrate how model-based predictions of both escapee dispersal and genetic impacts can be used to inform both aquaculture management decisions and wild salmon conservation.

Low-technology recirculating aquaculture system integrating milkfish Chanos chanos, sea cucumber Holothuria scabra and sea purslane Sesuvium portulacastrum

Abstract: Closed recirculation aquaculture systems (RAS) in combination with integrated multitrophic aquaculture (IMTA) are considered best management practices, but high material costs and difficult maintenance still hinder their implementation, especially in developing countries and the tropics. Few case studies of such systems with tropical species exist. For the first time, an extremely low-budget system was tested combining the halophyte sea purslane Sesuvium portulacastrum and a detritivore, sandfish Holothuria scabra, with finfish milkfish Chanos chanos over 8 wk on Zanzibar, Tanzania. In a 2 m3 RAS, milkfish and sea purslane showed good growth, producing an average (±SD) of 1147 ± 79 g fish and 1261 ± 95 g plant biomass, while sea cucumber growth was variable at 92 ± 68 g. The system operated without filter units and did not discharge any solid or dissolved waste. Water quality remained tolerable and ammonia levels were reliably decreased to <1 mg l−1. A NO2 peak occurred within the first 30 d, indicating good biofilter performance of the different system compartments. Changes in dissolved inorganic nitrogen (DIN) species support the notion that the sea cucumber tank was the main site of nitrification, while the hydroponic halophyte tank acted as a net sink of NO3. A nitrogen budget accounted for 63.7 ± 5.3% of the nitrogen added to the system as fish feed. Increasing the plant to fish biomass ratio to 5:1 would fully treat the DIN load. The experiment provides proof-of-concept of a simple pilotscale RAS, integrating tropical species at 3 trophic levels.

Carbon budgets of two typical polyculture pond systems in coastal China and their potential roles in the global carbon cycle

Abstract: The role of aquaculture systems in the global carbon cycle is poorly understood to date. We investigated the carbon budgets in 2 polyculture systems (PM: swimming crab Portunus trituberculatus with kuruma shrimp Marsupenaeus japonicus; and PMR: crab, shrimp and shortnecked clam Ruditapes philippinarum) during the farming season (125 d in total). The main carbon input occurred via water (PM: 55.06%; PMR: 62.50%), followed by that via feed. PM absorbed 21.55 g C m−2 across the air−water interface, accounting for 13.27% of the total input. The carbon output via water was the main output in both PM (89.17%) and PMR (46.43%). PMR emitted 53.00 g C m−2 into the atmosphere during the farming season, accounting for 32.53% of the total output. The carbon output by harvested animals in PMR accounted for 19.48% of the total output, which was much higher than that in PM (5.71%). Carbon accumulation in the sediment was significantly higher in PM than in PMR (p < 0.05), but the value of both represented a small portion of the total output. Clam farming in the polyculture system profoundly altered the carbon budgets by changing the CO2 flux direction, reducing carbon accumulation in water and sediments and increasing the carbon output by harvested animals. In terms of the global warming potential, which was calculated from the results of CO2 and CH4 fluxes across the air−water interface, PM had the potential for mitigating the greenhouse effect on the 20 yr horizon, whereas PMR exacerbated global warming. Our results suggest that PM acted as a net carbon sink in the global carbon cycle, while PMR acted as a carbon source.

The impact of aquaculture soundscapes on whiteleg shrimp Litopenaeus vannamei and Atlantic salmon Salmo salar

Abstract: Research into the effects of soundscapes on aquaculture species in key production systems is sparse, despite potential impacts of sound on animal welfare and commercial yields. In the following study, 2 high-value global aquaculture species, whiteleg shrimp Litopenaeus vannamei and Atlantic salmon Salmo salar, were exposed to aquaculture production system soundscapes. For shrimp, sound recordings of a commercial recirculating aquaculture system (RAS) were played back at a sound pressure level (SPL) of 128 dB re 1 μPa, and for salmon, recordings from a commercial sea pen production system were played back at an SPL of 127 dB re 1 μPa for an 8 wk period. Effects of exposure on growth, survival, and indications of metabolic stress were measured as parameters of interest for aquaculture production. Mean growth performance and survival rates did not differ significantly between sound and control treatments for either species. Blood and haemolymph parameters from both species indicated no measurable change in metabolic status or stress levels. Slight, but non-significant, increases in total haemocyte count and, in particular, hyaline cell count were recorded in shrimp exposed to sound. Slight, but non-significant reductions in overall weight gain were recorded in sound-exposed salmon. Overall, the results indicate that sound exposure in current production systems does not negatively affect the early grow-out stage of these key species, either due to rapid habituation or higher hearing thresholds of hatchery-produced individuals, and that no measurable stress response occurs in sound-exposed animals. In future studies, response of the studied species to acute sound exposure and the response of earlier, and potentially more sensitive, life-stages will need to be determined to ensure optimal welfare and production performance.

On the edge: assessing fish habitat use across the boundary between Pacific oyster aquaculture and eelgrass in Willapa Bay, Washington, USA

Abstract: This work was funded in part by2 NOAA NMFS Saltonstall-Kennedy grants (2014/2015NOAA-NMFS-FHQ-2015-2004246 and 2016/2017 NA16NMF4270254), a 2016−2018 Oregon State University Agricultural Research Foundation grant to F.T., and projectfunds of the USDA Agricultural Research Service (CRIS Pro-ject 2072-63000-004-00D).

Deposition of shells modify nutrient fluxes in marine sediments: effects of nutrient enrichment and mitigation by bioturbation below mussel farms

Abstract: Farming of extractive species such as filter feeding bivalves has been proposed as a potential method to mitigate impacts of eutrophication in marine environments. For such efforts to be sustainable, potential negative effects from mussel farms, such as accumulation of biodeposits in sediment below them, need to be considered and addressed. Benthic burrowing macrofauna strongly influence biogeochemical processes in soft bottom marine habitats by sediment reworking and irrigation and, thus, have the potential to mitigate some of the negative impacts. However, not all biodeposits are organic matter; shells that accumulate on and in the sediment below mussel farms also have the potential to influence processes in the sediment, the activity of bioturbators and the fluxes across the sediment-water interface. In this study, we evaluated the mitigation potential of the bioturbating polychaete Hediste diversicolor in sediments enriched with mussel waste material and the relative impact of mussel shells within the sediment matrix. The polychaetes generally increased fluxes and sediment oxygen uptake. With an observed tendency of increased fluxes of nutrients in sediments containing shells compared to sediments without, the results indicate that the accumulation of shell has a potential to further increase the mitigative effect of the polychaetes by influencing the solute fluxes across the sediment-water interface.

Mortality in the rockpool shrimp Palaemon elegans following long-term exposure to low doses of the anti-parasitic drug teflubenzuron

Abstract: Anti-parasitic drugs used to control sea lice infestations in the salmonid aquaculture industry are a growing environmental concern due to their potential impacts on non-target crustacean species. This study examined the lethal effects of teflubenzuron, a common in-feed pharmaceutical drug used on Norwegian salmon farms, on a non-target species, rockpool shrimp Palaemon elegans, following an extended exposure period. The standard daily dose for treating salmon is 10 μg teflubenzuron g−1 fish. Adult shrimp were fed 1 of 6 low doses of teflubenzuron (0, 0.0025, 0.005, 0.05, 0.094, 0.188 and 1.88 μg g−1) twice a week for a period of 66 d. Cumulative mortality reached 15, 27, 82 and 100% amongst shrimp exposed to the highest treatment groups (0.05, 0.094, 0.188 and 1.88 μg g−1, respectively). Cumulative mortality amongst shrimp exposed to the 2 lowest teflubenzuron doses and control feed was low (5%). Dose response curves based on measured concentrations within the shrimp were used to calculate a series of lethal threshold concentrations (LCx). The LC5, LC50 and LC90 concentrations of teflubenzuron causing low, median and high levels of mortality in rockpool shrimp were estimated to be 1.2, 18.4 and 150.6 ng g−1, respectively. These concentrations are similar to those reported in wild crustacean species, including shrimp species in the vicinity of Norwegian fish farms, both during and after teflubenzuron medication, suggesting that exposure to low doses of this compound can pose a significant risk to wild shrimp populations.

Optimal estimation of lice release from aquaculture based on ambient temperatures

Abstract: Models for mapping and forecasting infective pressure from salmon louse Lepeo phtheirus salmonis larvae are of major importance in the Norwegian government’s management of salmonid aquaculture. These models use site-reported temperature and number of eggproducing female adult lice present within cages to calculate how many lice eggs and larvae are released from individual farms. The reported temperature is critical in this calculation, as temperature influences both frequency of ‘spawnings’ and egg developmental time until hatching. Farms report temperature measured at 3 m depth, as defined by regulation. However, the salmon themselves, and therefore also the attached female lice and their eggs, often swim deeper to meet their preferred temperature within the water column. This study compares calculated lice egg production based on reported temperature at 3 m depth to calculated lice egg production based on a hydrodynamic ocean model of temperature stratification and salmon-preferred temperature in the modelled stratifications. The results clearly show that present legislated routines with farm site temperature measurements at 3 m depth lead to underestimation of egg and larvae production in winter and overestimation in summer for a range of sites. Future mitigating management and models of lice output should use the temperature measured or modelled for the depths the salmon predominantly occupy.

Machine learning analyses of bacterial oligonucleotide frequencies to assess the benthic impact of aquaculture

Abstract: Aquaculture is a rapidly expanding industry and is now one of the primary sources of all consumed seafood. Intensive aquaculture production is associated with organic enrichment, which occurs as organic material settles onto the seafloor, creating anoxic conditions which disrupt ecological processes. Bacteria are sensitive bioindicators of organic enrichment, and supervised classifiers using features derived from 16s rRNA gene sequences have shown potential to become useful in aquaculture environmental monitoring. Current taxonomy-based approaches, however, are time intensive and built upon emergent features which cannot easily be condensed into a monitoring pipeline. Here, we used a taxonomy-free approach to examine 16s rRNA gene sequences derived from flocculent matter underneath and in proximity to hard-bottom salmon aquaculture sites in Newfoundland, Canada. Tetranucleotide frequencies (k = 4) were tabulated from sample sequences and included as features in a machine learning pipeline using the random forest algorithm to predict 4 levels of benthic disturbance; resulting classifications were compared to those obtained using a published taxonomy-based approach. Our results show that k-mer count features can effectively be used to create highly accurate predictions of benthic disturbance and can resolve intermediate changes in seafloor condition. In addition, we present a robust assessment of model performance which accounts for the effect of randomness in model creation. This work outlines a flexible framework for environmental assessments at aquaculture sites that is highly reproducible and free of taxonomy-assignment bias.

Application of polychaetes in (de)coupled integrated aquaculture: an approach for fish waste bioremediation

Abstract: Development of benthic components within integrated multi-trophic aquaculture (IMTA) systems warrants more attention, and the development of polychaetes as an extractive component in IMTA systems is ongoing. This study estimates the bioremediation potential of Capitella sp. and Ophryotrocha craigsmithi for coupled and decoupled salmon-driven IMTA. In coupled IMTA, polychaetes receive fresh faeces, while in decoupled IMTA, preservation of faeces is applied. Respiration and ammonia excretion rates were measured for polychaetes fed fresh, oven-dried or acidified salmon faeces, and combined with nutrients incorporated into tissue growth, to estimate nutrient requirements. Nutrient requirements were subsequently used to evaluate bioremediation potential. Metabolic rates were highest for O. craigsmithi and contributed notably to their overall nutrient requirement (20-30%). For the 2 polychaete species, nutrient requirements ranged from 5 to 26 mg C and from 2 to 6 mg N g-1 AFDW d-1. These requirements were comparable with or higher than other polychaete species, highlighting the potential for fish waste bioremediation by Capitella sp. and O. craigsmithi. Preserved diets reduced bioremediation potential 1.5 and 3-5 times for, respectively, Capitella sp. and O. craigsmithi. Assuming that polychaetes are efficient fish-faeces convertors, the bioremediation potential indicates that benthic cultivation units containing 65000-95000 ind. m-2 of Capitella sp. or 36000-194000 ind. m-2 of O. craigsmithi can convert the daily organic waste flux deposited below an average salmon farm. These densities were within ranges reported for wild populations, indicating that, based on the bioremediation potential, development of benthic IMTA with these 2 polychaete species seems realistic and efficient for waste conversion.

Effects of cold stress and starvation on the liver of yellow drum Nibea albiflora: histological alterations and transcriptomic analysis

Abstract: The yellow drum Nibea albiflora is a marine fish of great economic value in China. Despite efforts to improve yields, aquaculture of this species has been hindered by increases in winter-related mortalities associated with cold temperatures and associated natural fasting periods. To better understand the molecular mechanisms that regulate stress responses in yellow drum during periods of cold and starvation, the effect of these stresses on the liver was investigated by performing comparative analyses among fish subjected to different temperatures and feeding strategies. The experiment lasted for 22 d and involved 4 groups: one fed group (control) and one fasted group at 16°C, and one fed group and one fasted group at 8°C. Our results showed that all stress-treated groups exhibited body weight loss during the experiment, demonstrating that both cold stress and fasting caused growth inhibition, but only the fish in the fasted group at 16°C showed a loss in the liver/body ratio, suggesting that starvation can cause mass loss in the liver while cold stress can result in mass loss in both liver and other tissues. Histological alterations were observed in the liver cells from stress-treated groups, also indicating mass loss in the liver during cold stress and starvation. Transcriptomic analysis showed that genes related to the meta bolism of carbohydrates, lipids and amino acids were the most enriched differentially expressed genes during the challenge conditions. These findings can help reveal molecular mechanisms regulating the stress responses of yellow drum exposed to cold and starvation.

Oyster aquaculture does not impede spawning beach access for Atlantic horseshoe crabs Limulus polyphemus

Abstract: Farms for eastern oyster Crassostrea virginica, which are commonly located along shallow estuarine shores of the eastern USA, use a range of farm equipment and require regular access to care for and harvest oyster livestock. In some cases, these farms are located in areas used by Atlantic horseshoe crabs Limulus polyphemus as they come ashore during spring to spawn. The sandy shores of the Delaware Bay host the largest spawning aggregations of this species in the world. Limited studies have examined interactions between horseshoe crabs and intertidal oyster farms, and concern has been raised about the horseshoe crab’s ability to traverse oyster farms to reach spawning habitat. This study examines potential farm interactions with horseshoe crabs in Delaware Bay during the 2018 and 2019 crab spawning season. Our studies included a range of experiments and surveys during high and low tide to observe crab abundance and behavior at rack-and-bag oyster farm and non-farm sites. In all cases, results indicated that crabs can successfully traverse rack-and-bag farms and reach spawning beaches. Crabs do not differentially use farm versus non-farm areas, and crab behavior is relatively unaltered by farm gear. These results provide important context for developing frameworks for managing ecological interactions among farms and wildlife species of concern.