Sea-cage Aquaculture Research Articles

Culture system impact on fatty acids and amino acids accumulation in tiger pufferfish (Takifugu rubripes)

Tiger pufferfish (Takifugu rubripes) is considered to be the most nutritionally valuable aquaculture species due to its high protein and collagen content. In this study, the fatty acids and amino acids (AAs) of the muscle and skin of tiger pufferfish reared in an offshore sea cage aquaculture system (OSCS) and a recirculating aquaculture system (RAS) were examined to illustrate the possible differences between the two systems. Results showed that the saturated fatty acid (SFA), arachidonic acid, and polyunsaturated fatty acid (PUFA) content of tiger pufferfish reared in the OSCS were significantly higher than those of pufferfish reared in the RAS. Meanwhile, the contents of C14:0, C16:1n-7, C18:1, and C18:2 were significantly higher in the muscle of male pufferfish than in females. The fatty acid content in the skin of tiger pufferfish manifested similar results in the muscle, and pufferfish raised in the OSCS obtained higher values of SFA, PUFA and monounsaturated fatty acid than did pufferfish reared in the RAS. The docosahexaenoic acid and eicosapentaenoic acid content in the skin of male pufferfish were significantly higher than those of females reared in the RAS, whereas there was no significant difference between male and female fish reared in the OSCS. Essential amino acid (EAA), non-essential amino acid (NEAA), and flavor amino acid (FAA) content in the muscle and skin of pufferfish reared in the OSCS were significantly higher than those of fish reared in the RAS. However, EAA content in the muscle and skin of pufferfish reared in the two aquaculture systems showed no significant difference. EAA, NEAA, and FAA content in the muscle and skin of male tiger pufferfish were higher than those of female pufferfish reared in the RAS, whereas no significant difference was observed in male and female pufferfish reared in the OSCS. The interaction effects of gender and rearing system on fatty acid and AAs content in the muscle and skin of tiger pufferfish were observed. In conclusion, the accumulation of fatty acids and AAs in OSCS-raised tiger pufferfish was higher than that in RAS-raised fishes, and male tiger pufferfish had a significant advantage. These findings provide the basic data and will be helpful in developing new strategies for enhancing the flesh quality of tiger pufferfish through the combined land-sea (RAS-OSCS) relay model in captivity.

Wooden traps can replace coral stone traps harvesting the wild lobster seed in mitigating the negative impact on the marine environment

Lobster seacage aquaculture has a significant social-economic contribution to many coastal communities throughout the central provinces of Vietnam. One of the issues of lobster aquaculture is that the industry entirely relies on the wild juvenile lobster (lobster seed) captured using traps made of coral stones, which affects the coastal ecology and environment. The present study was carried out to compare the catch efficiency of traps made of round timber poles (wooden trap) with conventional dead corals (coral stones) during the juvenile lobster fishing season in 2019 in the coastal area of Nha Trang city, Vietnam. Results showed that experimental wooden traps maintained the conventional catch rate level, with a significant proportion of Panulirus ornatus caught at larger carapace length than those caught by the coral stone traps. Our findings show the biological and environmental benefits of using alternative fishing methods would eliminate collecting coral stones to make lobster seed traps and contribute to coastal protection while maintaining the fishing operation and seed supplies for the lobster seacage farmers.

Effect of sea cage aquaculture on the length, weight, and condition of wild Atlantic cod Gadus morhua

Wild fish have been shown to associate with sea cage aquaculture and consume waste feed; however, little is known about the effects of waste feed consumption on wild fish. We used Atlantic cod Gadus morhua collected in the direct vicinity of sea cages and reference Northwest Atlantic Fisheries Organization divisions, either outside the direct vicinity (‘local division’) or completely removed from aquaculture (‘outside divisions’), to compare length, weight, and condition for cod ages 2 to 4. Concentrations of vegetable oil-based fatty acids (linoleic acid and α-linolenic acid) were then used as biomarkers for waste feed consumption to determine their role in explaining differences in length, weight, and Fulton’s condition index among cage-associated cod. Age 2 cage-associated cod were in lower condition than age 2 cod from the local division and lighter than age 2 cod from all outside divisions. Age 3 cage-associated cod were comparable to age 3 cod from the local division but in lower condition than age 3 cod from all outside divisions. However, age 4 cage-associated cod were longer and heavier than age 4 cod from the local division, but in lower condition than age 4 cod from 2 of 3 outside divisions. Additionally, there were positive relationships between fatty acid concentrations and length and weight for age 2 cage-associated cod, but no significant relationships for age 3 or 4 cage-associated cod. Results suggest the effects of waste feed consumption are contradictory but not consistent enough to disrupt established growth and condition patterns among divisions.

The variation of intestinal autochthonous bacteria in cultured tiger pufferfish Takifugu rubripes.

Intestinal autochthonous bacteria play important roles in the maintenance of the physiological homeostasis of animals, especially contributing to the host immune system. In the present study, the variation of autochthonous bacterial community in the intestinal tract of 2-7 months-old tiger pufferfish Takifugu rubripes and bacterial communities in the seawater of recirculating aquaculture system (RAS) and the following offshore sea cage aquaculture system (OSCS) were analyzed during the aquaculture period from May to October 2021. Proteobacteria was found to be the most dominant phyla in both intestinal and seawater bacterial communities, which accounted for 68.82% and 65.65% of the total bacterial abundance, respectively. Arcobacter was the most core bacterial taxon in the intestinal bacterial community, with the most dominant abundance (42.89%) at the genus level and dominant positions in co-occurrence relationships with other bacterial taxa (node-betweenness value of 150). Enterococcaceae was specifically enriched in the intestinal bacterial community of pufferfishes from RAS, while Vibrionaceae was enriched in the intestinal bacterial community from OSCS. The F-values of beta diversity analysis between intestinal and seawater bacterial communities generally increased from May (6.69) to October (32.32), indicating the increasing differences between the intestinal and seawater bacterial communities along with the aquaculture process. Four bacterial taxa of Weissella sp., Akkermansia muciniphila, Dietzia sp. and Psychrobacter pacificensis had significant correlations with immune response parameters, and they were suggested to be the indicators for immune status and pathological process of pufferfish. The knowledge about the specific core bacteria, potentially pathogenic bacteria and the change of bacterial community in the intestinal tract of cultured pufferfish is of great scientific significance and will contribute to the understanding of intestinal bacterial homeostasis and biosecurity practice in pufferfish aquaculture.

Elemental Fingerprinting of Wild and Farmed Fish Muscle to Authenticate and Validate Production Method.

In the context of expanding fish production and complex distribution chains, traceability, provenance and food safety tools are becoming increasingly important. Here, we compare the elemental fingerprints of gilthead seabream (Sparus aurata) muscle from wild and different aquaculture productions (semi-intensive earth ponds and intensive sea cages from two locations) to confirm their origin and evaluate the concentrations of elements with regulatory thresholds (Cu, Hg, Pb and Zn). Using a chemometric approach based on multi-elemental signatures, the sample origin was determined with an overall accuracy of 90%. Furthermore, in a model built to replicate a real-case scenario where it would be necessary to trace the production method of S. aurata without reliable information about its harvesting location, 27 of the 30 samples were correctly allocated to their original production method (sea-cage aquaculture), despite being from another location. The concentrations of the regulated elements ranged as follows: Cu (0.140–1.139 mg/Kg), Hg (0–0.506 mg/Kg), Pb (0–2.703 mg/Kg) and Zn (6.502–18.807 mg/Kg), with only Pb presenting concentrations consistently above the recommended limit for human consumption. The present findings contribute to establishing elemental fingerprinting as a reliable tool to trace fish production methods and underpin seafood authentication.

Comprehensive lipid profiles of sea cage aquaculture cobia (Rachycentron canadum) based on lipidomics

Cobia (Rachycentron canadum) is a significant fish species for mariculture with high nutritional value. This research aims to comprehensively investigate the lipid profiles of cobia tissues, including fatty acid profiles, characteristics of phospholipids (PL) and triacylglycerols (TAG), and lipid molecular species. The results showed that cobia contained high levels of total lipids (2.89 −32.09 % of wet weight), docosahexaenoic acid (DHA, 10.83 −14.69 % of total fatty acids) and eicosapentaenoic acid (EPA, 3.54 −9.68 %). Compared with TAG, higher levels of polyunsaturated fatty acids, DHA/EPA in particular, were concentrated in PL. Interestingly, DHA was predominantly distributed in the sn-1 position of PL and the sn-2 position of TAG, whereas EPA was predominantly distributed in the external positions of PL and TAG. Additionally, at least 693 molecular species from 23 subclasses were identified by ultrahigh-performance liquid chromatography-quadrupole exactive-mass spectrometry (UPLC-Q-Exactive-MS). Glycerophospholipids (63.19 −66.61 %) and glycerolipids (19.17 −22.21%) were the major lipid classes in cobia tissues, and the majority of them contained DHA and EPA. Hence, this comprehensive analysis will help to evaluate the lipid nutritional values and facilitate exploitation in cobia consumption and processing.

Summer Is Coming! Tackling Ocean Warming in Atlantic Salmon Cage Farming.

Simple SummaryAtlantic salmon (Salmo salar) has become a commodity worldwide. The culture of Atlantic salmon is by far the most well-developed branch of marine finfish aquaculture, with this species ranking among the top ten most highly produced in global aquaculture. While Atlantic salmon has been commonly farmed in sea cages located in colder waters (e.g., in Norway, Chile and Tasmania), these regions can experience the negative impacts of heat waves that push seawater temperature above values tolerated by this species. These climate-change-driven shifts in water temperature can be associated with mass mortality events and urgent actions are needed to cope with a changing ocean. This paper reviews the thermal limits of adult Atlantic salmon and lists the negative effects driven by heat stress. We highlight how biotechnology and the genetic diversity of wild populations may help producers to tackle this challenge. Selective breeding programs and other more advanced biotechnological solutions (e.g., gene editing) may play a key role in this quest to produce new strains of Atlantic salmon that more readily tolerate higher water temperatures, without compromising productivity and profitability.Atlantic salmon (Salmo salar) cage farming has traditionally been located at higher latitudes where cold seawater temperatures favor this practice. However, these regions can be impacted by ocean warming and heat waves that push seawater temperature beyond the thermo-tolerance limits of this species. As more mass mortality events are reported every year due to abnormal sea temperatures, the Atlantic salmon cage aquaculture industry acknowledges the need to adapt to a changing ocean. This paper reviews adult Atlantic salmon thermal tolerance limits, as well as the deleterious eco-physiological consequences of heat stress, with emphasis on how it negatively affects sea cage aquaculture production cycles. Biotechnological solutions targeting the phenotypic plasticity of Atlantic salmon and its genetic diversity, particularly that of its southernmost populations at the limit of its natural zoogeographic distribution, are discussed. Some of these solutions include selective breeding programs, which may play a key role in this quest for a more thermo-tolerant strain of Atlantic salmon that may help the cage aquaculture industry to adapt to climate uncertainties more rapidly, without compromising profitability. Omics technologies and precision breeding, along with cryopreservation breakthroughs, are also part of the available toolbox that includes other solutions that can allow cage farmers to continue to produce Atlantic salmon in the warmer waters of the oceans of tomorrow.

Random forest-based understanding and predicting of the impacts of anthropogenic nutrient inputs on the water quality of a tropical lagoon

Seawater quality degradation is caused by diverse, non-linearly interacting factors, knowledge of which is essential for understanding and predicting water quality trends. Currently, most water-quality research has been based on certain assumptions to employ linear approaches for solving simplified problems, such as numerical simulations or cumulative impact assessments. To improve the accuracy and ease of prediction, the random forest method has been increasingly employed as a good alternative to traditional prediction methods. In the present study, the random forest method was adopted to construct a model of the water quality response of Xincun Lagoon to anthropogenic nutrient inputs based on a limited amount of sample data, aiming to (a) identify the critical sources of nutrient inputs that affect the meeting of water quality objectives so as to minimize the socioeconomic impact on secondary stakeholders; and (b) predict the impact of a reduction of anthropogenic nutrient inputs on water quality improvement. It can be seen from the results that the intensity of stressors generated by different human activities presents an obvious non-linear superposition pattern, and the random forest method is one of the feasible solutions to this phenomenon; in addition, the impact on the lagoon ecosystem is not directly related to the intensity of the pressure source, for example, coastal aquaculture is more important than shallow sea cage aquaculture. Therefore, the method established in this paper can be used to identify the key pressure sources during the restoration of the lagoon environment, so as to achieve the unity of economy and effectiveness.

Ege Denizi'nde ağ kafes yetiştiriciliğinde dalış faaliyetlerinin değerlendirilmesi

Mariculture represents approximate 50 percent of global aquaculture production by weight. Fish cages, which consist simply HDPE frame, netting, and mooring system, in fish farming are key elements of sea cage aquaculture. Aquaculture divers are responsible for inspection and maintenance of the underwater structures such as nets, mooring line and anchor, removing dead fish, monitoring the abnormal behavior of fish, assistance harvesting of fish and other periodic underwater works in fish cage farms. In recent years, the demand for aquaculture divers has increased in fish cage farms in both northern and southern Aegean Sea with enhancement of fish production in mariculture. On the other hand, various problems (diving accidents, faulty diving operations, lack of training etc.) related to work conditions and legal regulations of aquaculture divers have emerged. In the study, with the questionnaire consisting of 49 questions, face to face surveys were performed with 162 aquaculture divers in fish farms around Muğla and İzmir provinces between February and May 2019. Results showed the presence that there are three main problems consisting of diving regulations for professional divers, the candidate diving system and diving education which may cause fatal accidents should be improved and revised urgently.

Sea cage aquaculture may provide an energetic subsidy to wild juvenile cod in coastal bays of southern Newfoundland, Canada

Sea cage aquaculture can alter the spatial distribution of wild fish populations; however, little is known about the dietary habits of wild fish frequenting sea cages. We used wild juvenile cod Gadus morhua reared in the laboratory and fed either an aquafeed pellet or marine-based diet to determine trophic discrimination factors (TDFs) of stable carbon (δ13C) and nitrogen (δ15N) isotope values in white muscle tissue and baseline liver proportions of vegetable-oil based (VOB) fatty acids. We then used δ13C and δ15N and proportions of VOB fatty acids to investigate the dietary habits of wild cage-associated juvenile and adult Atlantic cod and adult Atlantic redfish Sebastes fasciatus. Cod and redfish were collected in the immediate area of sea cages and reference areas of no aquaculture production. Juvenile cod captured around sea cages had both elevated δ13C and δ15N values and proportions of VOB fatty acids, and isotopic fractionation comparable to laboratory cod fed an aquafeed diet. However, differences in δ13C and δ15N and proportions of VOB fatty acids between cage-associated and reference site adult cod and redfish were predominately absent. Results suggest that sea cages may provide an energetic subsidy to juvenile cod but perhaps not at the level to sustain adult cod or redfish. Therefore, the lack of differences suggests that both adult groups may be using cage sites opportunistically and only for short duration, as isotopic values and fatty acid proportions were not consistent with waste feed consumption despite individuals being collected in close proximity to sea cages.

Environmental characteristics and development prospective of sea cage aquaculture in Morotai Island Regency

Sea cage aquaculture, if well managed, is one of the most successful and profitable marine aquaculture systems and has demonstrated substantial economic benefits. A relatively suitable sea or coastal water quality, as well as availability waters areas, are the major supporting factors that enable successful sea cage culture. This study explores the environmental characteristics and the potential development of sea cage culture in Morotai Island Regency, North Maluku Province. This study employed a survey method by which environmental data were collected following a random stratified technique in geographical information systems (GIS). The results of water quality analysis generally indicated that the study areas are highly suitable for sea cage culture. The suitability of engineering design based on water depth and safety issues relating to extreme weather and highly exposed coastal areas was the only significant factor that directly limits the suitable areas. After the integration of water depth and safety factors variable into the final spatial analysis, only 398 ha of waters were found suitable for sea cage culture. However, previous studies have suggested that for the sake of sustainability, only a maximum 10% of suitable waters can be used for the sea cage culture. Therefore, this study has recommended no more than 15 units of cages per hectare with a dimension of 8 x 8 m2 per cage or only the 597 units to be allocated for the whole identified suitable areas. A lack of marine aquaculture infrastructure and an inadequate as well unreliable supply of quality fish seed (fry) have been the major constraints for the sustainable production and operation of sea cage aquaculture in the study areas. With a better understanding of the existing suitable areas and its maximum production carrying capacity, aquaculture decision-makers can develop effective and efficient strategies to help improve the product for the sustainability sea cage culture activities in this region.

Acoustic Telemetry: A Tool to Monitor Fish Swimming Behavior in Sea-Cage Aquaculture

Acoustic telemetry techniques are very useful tools to monitor in detail the swimming behaviour and spatial use of fish in artificial rearing environments at individual and group levels. We evaluated the feasibility of using passive acoustic telemetry to monitor fish welfare in sea-cage aquaculture at an industrial scale, characterizing for the first time the diel swimming and distribution patterns of gilthead seabream (Sparus aurata) at fine-scale. Ten fish were implanted with acoustic tags equipped with pressure and acceleration sensors, and monitored in a commercial-size sea-cage for a period of one month. Overall, fish exhibited clear differences in day vs night patterns both on swimming activity and vertical distribution throughout the experiment. Space use increased at night after the implementation of structural environmental enrichment in the sea-cage. Acoustic telemetry may represent an advancement to monitor fish farming procedures and conditions, helping to promote fish welfare and product quality.

Altered hepatic glycolysis, lipogenesis, and blood biochemistry of tiger puffer (Takifugu rubripes) under two different culture systems

Tiger puffer (Takifugu rubripes) is one of the most commercially important fish species cultivated and consumed in East Asian countries, including Japan, South Korea and China. In this study, the hepatic glycolysis, and lipogenesis, and serum biochemistry of tiger puffers subjected to short-term culture in offshore sea cage aquaculture system (OSCS) and recirculating aquaculture system (RAS) were evaluated. Results showed that the activity of hepatic phosphofructokinase, and lipoprotein lipase, ATP level, and serum cortisol content of the male tiger puffers reared in OSCS were significantly higher than those of female tiger puffers reared in OSCS and those of fish reared in RAS. The lowest hepatic fatty acid synthetase activity, lipid droplet number, serum aspartate aminotransferase activity, Na+ and Cl− concentrations were observed in male tiger puffers reared in OSCS. However, serum glucose, triglyceride, total cholesterol, K+ concentrations and alanine aminotransferase activity of tiger puffers reared in RAS and OSCS showed no significant differences. Hepatic glycolysis and lipogenesis were profoundly affected by rearing system and gender. The interaction effect of gender and rearing system on hepatic lipoprotein lipase activity, lipid droplet number and serum Na+ level was observed. These results indicate male tiger puffers exhibited different metabolic status in hepatic glycolysis, lipogenesis, and serum biochemical parameters when reared under two different culture systems. These findings will provide important information for improving tiger puffer (Takifugu rubripes) farming and profitable production using the RAS and OSCS aquaculture systems in the north coast of China.

Effects of laboratory salmon louse infection on osmoregulation, growth and survival in Atlantic salmon.

Anadromous Atlantic salmon (Salmo salar) rely on long ocean migrations to build energy stores for maturation and spawning. In seawater, wild Atlantic salmon are threatened by high salmon lice (Lepeophtheirus salmonis) infestation levels resulting from intensive salmonid sea-cage aquaculture. Salmon lice infection can cause a stress response and an osmotic imbalance in the host. The lice infection intensity threshold values for these responses, however, remain to be identified in Atlantic salmon. In order to define this under laboratory conditions, individually tagged F1 wild origin Atlantic post-smolts (40 g) were infected with salmon lice copepodids or left as uninfected controls. Twenty-eight days post infection, infected post-smolts had a mean of 0.38 (range of 0.07–0.9) mobile lice g−1 fish weight. During this period, specific growth rates (SGRs) were lower in infected than control fish (0.4 vs 1.0% day−1). Higher plasma Na+, Cl− and osmolality in infected fish also indicate osmoregulatory impairment. SGR correlated negatively with plasma Na+, Cl−, osmolality and cortisol in the infected, but not in the control group. Infection intensity (lice g−1 fish) correlated positively with mortality rate and plasma Na+, Cl−, osmolality and cortisol and correlated negatively with SGR and condition factor. Calculated lice intensity threshold values for changes in plasma ions were 0.18 lice g−1 for plasma Cl−, and 0.22 lice g−1 for plasma Na+. Moribund infected fish occurred at infection intensities above 0.2 lice g−1, and these fish had extreme plasma Cl−, Na+, osmolality and cortisol levels. There was a positive correlation between plasma cortisol and plasma Na+, Cl− and osmolality in infected fish. This study provides vital information that can be used to define thresholds in the monitoring and conservation of wild Atlantic salmon populations affected by aquaculture-driven salmon lice infestations.

Numerical assessment of the environmental impacts of deep sea cage culture in the Yellow Sea, China

In light of environmental deterioration in coastal areas, deep sea cage aquaculture is becoming an increasingly attractive mode of mariculture. A key factor in determining the potential of deep sea cage aquaculture is to evaluate the environmental impacts of these practices. Here, a numerical model consisting of coupled hydrodynamic-, tracer-tracking- and 3-D Lagrangian particle-tracking models was set up and applied to evaluate the environmental impacts of deep sea cage cultivation of sea bass (Lateolabrax japonicus) in the Yellow Sea, China. The model was verified using water level data on August 1–31, 2018 and nutrient concentration in water and surface sediments in May, August, and November 2018, and January 2019. Results show that the model successfully captures the characteristics of local tidal currents and the total particulate nitrogen and phosphorus concentrations of the underlying sediments. Water quality simulations indicate that deep sea cages account for 26% of the total dissolved inorganic nitrogen and 19% of the active phosphorus content. Residual feed particles are predicted to fall in an ellipse centered on the cage location, with a long axis of 200 m and a short axis of 50 m. Feces are predicted to fall in an ellipse with a long axis of 1400 m and a short axis of 600 m. The Superposition particles are predicted to settle in an ellipse with a long axis of 320 m and a short axis of 150 m. The model results indicate that installation of all deep sea cages will lead to acceptable levels of water quality, but that sediments may become polluted. The coupled model can be used to predict the environmental impacts of deep sea cage farming and provide a useful tool for designing the layout of integrated multi-trophic aquaculture of organic extractive or inorganic extractive species.

Alternations in oxidative stress, apoptosis, and innate-immune gene expression at mRNA levels in subadult tiger puffer (Takifugu rubripes) under two different rearing systems

Tiger puffer (Takifugu rubripes) is one of the major aquaculture fish species in China due to its high economic value. In this study, the transcriptions of hepatic antioxidant enzyme, stress, apoptosis, and immune-related genes of sub-adult tiger puffers (Takifugu rubripes) were evaluated under two different rearing systems [offshore sea cage aquaculture system (OSCS) and recirculating aquaculture system (RAS)]. Results showed that the mRNA expression levels of the antioxidant enzyme (mn-sod, cu/zn-sod, gpx, and gr) and stress-related (hsp70 and hsp90) genes of male tiger puffers reared in the OSCS were significantly higher than female fish reared in the OSCS and fish reared in the RAS. The anti-apoptotic gene bcl2 exhibited the similar results. By contrast, the mRNAs of the pro-apoptotic genes (p53, caspase8, caspase9, and caspase3) of male tiger puffers reared in the OSCS were significantly lower than female fish reared in the OSCS and fish reared in the RAS. Male tiger puffers reared in the OSCS displayed significantly higher complement components (c3) and inflammatory cytokine (il-6) mRNAs, whereas B-cell activating factor (baf) and tumor necrosis factor α (tnf-α) mRNAs remained unchanged. Meanwhile, the mRNA levels of pro-apoptotic (bax, caspase8) and immunity-related (c3, il-6 and il-7) genes of female tiger puffers reared in the OSCS were significantly lower and higher than female fish reared in the RAS, respectively. In conclusion, the hepatic antioxidant, anti-apoptosis, and innate immunity of tiger puffers reared in the OSCS were better than fish in the RAS, male tiger puffer obtained the best values. These results expand the knowledge on the combined RAS and OSCS alternative aquaculture model for tiger puffers and aid in their management in captive.

Eco-Efficiency Assessment of Rockfish Sea-Cage Aquaculture Facility

Eco-Efficiency Assessment of Rockfish Sea-Cage Aquaculture Facility

Effects of laboratory salmon louse infection on Arctic char osmoregulation, growth and survival.

High salmon lice (Lepeophtheirus salmonis) infestation levels resulting from intensive salmonid sea-cage aquaculture can threaten populations of wild salmonid hosts. This includes anadromous Arctic char (Salvelinus alpinus), which rely on short migrations into more productive seawater environments to build energy stores for maturation, spawning and over-wintering in freshwater. Elevated salmon lice burdens may limit the benefits of migration by constraining osmoregulation, growth, survival and reproduction. To test for these effects, we simulated anadromous migration in tanks by transferring individually tagged Arctic char smolts (n = 352, averaging 133 g) to seawater where they were infected with salmon lice or left as uninfected controls for 1 month, and then transferring them back to freshwater for 2 months. After the seawater phase, infected post-smolts had a mean of 0.33 (range of 0.09–0.91) mobile lice g−1 fish weight. At this point, specific growth rates (SGRs) dropped in infected compared to control fish (0.1% vs. 1.6% day−1). Higher plasma Na+ and osmolality in infected fish also indicate osmoregulatory impairment. Throughout the study, mortality was 18.2% and 1.7% in infected and control groups, but sexual maturation was low and comparable between groups. Infection intensity correlated positively with mortality rate and plasma Cl−, and correlated negatively with SGR and condition factor (CF). CF dropped (ΔCF < 0) at intensities of >0.09 lice g−1 fish weight, and intensities of >0.3 causing zero or negative SGRs and increased mortality were particularly concerning. If infection intensities reach these levels in the wild, char could be impacted by growth restrictions and increased mortality rates, which potentially cause shorter migration durations, lowered reproductive success and possibly also selection against anadromy. This study provides vital information for conservation practitioners wanting to understand the physiologically derived burden salmon lice can have on Arctic char populations, and can be used to define thresholds in the monitoring and conservation of Arctic char populations affected by aquaculture-driven salmon lice infestations.

Sea-cage aquaculture impacts market and berried lobster (Homarus americanus) catches

Sea-cage aquaculture impacts market and berried lobster (Homarus americanus) catches

Antibiotic use in Vietnamese fish and lobster sea cage farms; implications for coral reefs and human health

Several papers have reported on the development of antibiotic resistance and implications for human medicine but fewer deal with environmental impacts of antibiotic use. Marine sea cage aquaculture in SE Asia is often established close to coral reef ecosystems. Large amounts of antibiotics are used in the cultivation of fish and lobster and hence released directly into the environment.This study investigates the antibiotic practices in sea cage farms producing fish and spiny lobster in Vietnam, mainly for the domestic market. There are approximately 3500 sea cage farms in Vietnam and we performed semi-structured interviews with 109 sea cage farmers asking them if they use antibiotics and if so; what sort/when/how often/how much.We found that the Vietnamese cage farmers are using antibiotics in an unstructured way, which seems to have little or no effect on the survival of the stock, or profit of the farm. The fact that the farmers live at their farm and use the sea next to the cages both for fishing and collecting filter-feeding bivalves for direct consumption, as well as a toilet, poses an additional risk for the spreading of human antibiotic resistant pathogens. Thirteen different antibiotics were found in the study. Eighty-two percentage of the lobster farmers and 28% of the fishfarmers used antibiotics. The average amounts used were over 5 kg per produced ton of lobster and about 0.6 kg per ton of fish, which is much higher than in other studies. Several antibiotic substances listed as “critical” and “highly important” for human medicine by WHO were used prophylactically and routinely with little control and enforcement of regulations.We tested and detected antibiotic resistance to Tetracycline, Vancomycin and Rifampicin in the coral associated bacteria Bacillus niabensis as far as 660 m from fish farms with resistance decreasing with distance from the cage farms. The antibiotics are likely to have negative effects on the coral-symbiont relationship adding further risks to an already stressed environment.