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In the realm of marine aquaculture, the netting of cages frequently accumulates marine fouling, which impedes water circulation and poses safety hazards. Traditional manual cleaning methods are marked by inefficiency, high labor demands, substantial costs, and considerable environmental degradation. This paper initially presents the current utilization of net-cleaning robots in the cleaning, underwater inspection, and monitoring of aquaculture cages, highlighting their benefits in enhancing operational efficiency and minimizing costs. Subsequently, it reviews key technologies such as underwater image acquisition, visual recognition, adhesion-based movement, efficient fouling removal, motion control, and positioning navigation. Ultimately, it anticipates the future trajectory of net-cleaning robots, emphasizing their potential for intelligence and sustainability, which could drive the marine aquaculture industry towards a more efficient and eco-friendly era.

The accumulation of biofouling organisms on farm infrastructure is an on-going problem for the global salmon aquaculture industry. Most salmon farmers in production regions worldwide undertake regular in situ net cleaning using specialised high-pressure washing rigs. Generally, the material removed from the net during cleaning is discharged into the surrounding environment. This ‘cleaning waste’ consists predominantly of biofouling organisms (intact and fragmented), but may also contain fish pathogens and antifouling coating particles containing biocides. The suspension, dispersal and deposition of this material are associated with a range of potential risks that can be grouped into 4 main categories: (1) health or disease risks (e.g. direct damage to sensitive tissues upon contact with cleaning waste, and facilitation of infection by pathogens); (2) deposition and pollution risks (impact on benthic communities around farms through deposition of organic material and antifouling biocides); (3) invasive species risks (localised dispersal of non-indigenous propagules and fragments); and (4) biofouling exacerbation (e.g. ‘self-seeding’ of downstream production cages). Here, we describe and discuss these 4 potential risks associated with in situ cleaning and present an agenda and research priorities to better understand and manage these risks.

Gill disease is a major threat to aquaculture of Atlantic salmon, with an unknown and likely underestimated contribution from cnidarians such as jellyfish and biofouling hydroids. To better understand the risk and thus enable mitigation, technology for the certain identification of cnidarian-related gill damage is needed. We used the hydroid Ectopleura larynx in a case study to determine whether the exposure of salmon to nematocyst-bearing hydrozoans can be deducted via non-destructive PCR-based methods. In a field experiment, we evaluated (i) whether swabbing the inside of the gill operculum in farmed Salmo salar and subsequent PCR analysis can provide quantifiable information about the presence of E. larynx material in the gill chamber and, if so, (ii) whether the screening results correlate with histological assessments of gill damage.   The developed PCR methods were able to detect the presence of biofouling hydroids in ambient water. However, despite exposure to suspended hydroid particle concentrations that did result in gill damage in some salmon, quantitative PCR results did not correlate with histological gill assessments. For opercular swabs to serve as a diagnostic tool for detecting biofouling-mediated gill damage in live salmon, increased specificity of genetic markers and improved sampling methods are needed. Animal trial permit no. 24252 (granted 06.07.2020, Norwegian Food Safety Authority).

Net cleaning robots have been playing an increasingly important role in offshore aquaculture due to their efficiency and labor-saving capabilities. However, in practice, these robots are still entirely teleoperated and require constant, skilled human operation. The mesh intersection points, which serve as a structural feature of the nets, provide valuable visual cues for robot self-localization and net damage identification. Therefore, the detection and tracking of these points are crucial for developing autonomous net cleaning robots. To achieve intersection point detection, we propose NPUNet-lite, a lightweight model based on U-Net. This model significantly minimizes computational resources and model size while preserving high detection accuracy. For reliable point tracking, we develop the NlPTrack algorithm, which incorporates an iterative closest point-based association strategy to meet spatial constraints between points within a frame, and a cascaded association strategy to satisfy homographic and epipolar constraints across adjacent frames. We build a dataset from videos collected during a robotic cleaning task to train and evaluate our methods. The experimental results indicate that our segmentation network achieves comparable accuracy to advanced networks, yet with a substantial reduction in computational cost. Meanwhile, the tracking method successfully tracks the majority of intersection points across scenarios where the robot moves in different directions.

The growth of biofouling on aquaculture infrastructure is a universal challenge. Standard industry practices to remove biofouling in finfish aquaculture typically include in situ net cleaning via power washing. Since those cleaning practices can be potentially harmful to fish-gill health and expensive, development of other non-toxic biofouling controls is an industry priority. Deposit-feeding sea cucumbers are potentially well suited for biofouling control due to their feeding mechanism, but remain relatively untested in this capacity. We examined the use of California sea cucumbers (Apostichopus californicus) to control biofouling on cages containing adult Chinook salmon (Oncorhynchus tshawytscha) at a commercial farming operation. Four cage types were established: cages with salmon and sea cucumbers, cages with salmon only, cages with sea cucumbers only, and cages without either species. Results showed that the sea cucumbers actively fed on biofouling when salmon were absent (~16% cleaner on average) but preferred to consume uneaten feed/faeces at the bottom of the cages, neglecting the biofouling, when the salmon were present. It is hypothesized that biofouling control in cages with salmon may be possible with an increased density of sea cucumbers. This is the first study to examine the use of sea cucumbers as a direct net biofouling control agent with adult fish. Our results will be beneficial for industry to develop standard operating procedures for using California sea cucumbers as a biofouling control and could contribute to the development of a management framework for sea cucumber/salmon integrated multi-tropic aquaculture.

Stress is a major concern in aquaculture production and more knowledge is needed on physiological responses towards different operational events. Few studies have been performed on fish reared in an actual commercial setting. Transferring salmon from hatchery to sea involves handling, crowding, pumping, transport as well as adjusting to a new environment. This case study investigates the relative expression of selected stress related-genes in farmed Atlantic salmon (Salmo salar) post-smolts that were relocated from land-based breeding tanks with few environmental stressors to sea phase with numerous environmental stressors and major management operations e.g. net pen cleaning. Gill tissue for analysis (n = 60) was harvested at four distinct time points: before, during, and 3 and 6 weeks after sea transfer. RT-qPCR was performed on a panel of 12 genes involved in different cellular pathways (alox5, cyp1α, hif1α, il4/13a, muc2, muc5, muc18, nrf2, pcna, phb, p38 and tnfα). While the transport process itself did not appear to induce notable stress levels, metabolic gene markers showed significant changes in expression after transfer to sea, implying cellular adaptations to sea phase. The occurrence of net pen cleaning induced a strong upregulation of pro-inflammatory markers (alox5, tnfα) and mucins (muc2, muc5 and muc18), suggesting their gene products to be relevant during this operational event. As p38 expression was significantly elevated during transport and after cage cleaning, we cautiously propose p38 as an interesting stress marker for future exploration. The study provides insight into the lives of farmed Atlantic salmon and demonstrates that timing of major operations is crucial to avoid accumulation of stress.

This study addresses the issue of biofouling on marine aquaculture cages, where organisms like algae and purple mussels negatively impact both the safety of the aquaculture environment and the integrity of the cages. To solve this problem, the paper introduces a cage cleaning device based on the cavitation jet principle. Using finite volume simulation software, the cavitation process of the device’s nozzle was modeled, with the gas-phase volume fraction used as the evaluation metric. Key experimental factors, such as the second section throat contraction angle, second section throat radius, and end diffusion angle, were analyzed through single-factor and quadratic regression orthogonal experiments to assess their effect on the cavitation performance. The optimal combination of nozzle parameters was determined to be a second section throat contraction angle of 41.047°, a second section throat radius of 0.834 mm, and an end diffusion angle of 35.495°. Under these conditions, the gas-phase volume fraction reached 0.941, indicating optimal cavitation performance. To validate these findings and further optimize the nozzle’s operational parameters, a nozzle cavitation test bench was constructed. Test results demonstrated that when the target distance was set at 15 mm and the angle at 20°, the surface roughness and maximum surface depth of the target were 6.215 μm and 22.030 μm, respectively, with the nozzle exhibiting the best cavitation effect at these settings. This nozzle design meets the requirements for efficient mesh cleaning, and the research provides valuable insights for future development and optimization of cleaning devices for aquaculture net cages.

The Ukraine conflict has put critical pressure on gas supplies and increased the price of fertilisers. As a consequence, biogas has gained remarkable attention as a local source of both gas for energy and biofertiliser for agriculture. Moreover, climate change-related damage incentivises all sectors to decarbonise and integrate sustainable practices. For instance, anaerobic digestion allows decarbonisation and optimal waste management. Incorporating a biogas system in each country would limit global warming to 2 °C. If suitable policies mechanisms are implemented, the biogas industry could reduce global greenhouse gas emissions by 3.29–4.36 gigatonnes carbon dioxide equivalent, which represent about 10–13% of global emissions. Here, we review the role of the biogas sector in capturing methane and mitigating carbon emissions associated with biogas outputs. Since biogas impurities can cause severe practical difficulties in biogas storing and gas grid delivering systems, we present upgrading technologies that remove or consume the carbon dioxide in raw biogas, to achieve a minimum of 95% methane content. We discuss the role of hydrogen-assisted biological biogas upgrading in carbon sequestration by converting carbon dioxide to biomethane via utilising hydrogen generated primarily through other renewable energy sources such as water electrolysis and photovoltaic solar facilities or wind turbines. This conceptual shift of 'power to gas' allows storing and utilising the excess of energy generated in grids. By converting carbon dioxide produced during anaerobic digestion into additional biomethane, biogas has the potential to meet 53% of the demand for fossil natural gas. We also evaluate the role of digestate from biogas systems in producing biochar, which can be used directly as a biofertiliser or indirectly as a biomethanation enhancement, upgrading, and cleaning material.

Background The use of insecticide-treated bed nets has been proven to be effective in reducing malaria transmission in highly endemic areas. Use of long-lasting insecticidal nets (LLINs) has been embraced by many malaria endemic countries. LLINs are up to 95% effective in inhibiting blood feeding, when used consistently even after 7 years. The challenge, however, is enhancing their consistent use, especially by the most vulnerable groups (children under 5 years and pregnant women). The study established factors associated with consistent use of bed nets for malaria control among children under 5 years in Soroti district. Methods The study employed a cross-sectional design, with multi-stage sampling of households. A total of 400 households (HH) were sampled and the HH head in each household interviewed. Key informant interviews (KIIs) were conducted with 7 key informants who were knowledgeable on the subject matter. Data analysis was done using SPSS 17.0 at Univariate, Bivariate and Multivariable levels; after entry and cleaning. Key informants’ data were summarized manually; verbatim quotes and text used to reinforce quantitative data in line with objectives. Results Only 56.8% of the 690 children under 5 years used bed nets consistently. The factors affecting consistent bed net use were age of the child, their use of bed nets the previous night, occupation of caretaker, respondents’ perceived susceptibility, perceived risk of getting malaria, size and shape of the bed nets. Rectangular nets were difficult to hang daily in huts according to most key informants. Conclusion Consistent bed net use among under fives is still below the RBM target of 85% by 2015 and can be enhanced by providing conical bed nets and setting aside a health education programme to emphasize the effectiveness of even one mosquito in spreading malaria at night to the entire household and ability of bed nets to stop transmission better than other methods.

Carbon dioxide removal (CDR) features prominently in the 1.5 °C compatible and high overshoot pathways in the IPCC’s Sixth Assessment Report (AR6, WGIII). However, the amount of CDR varies considerably among scenarios. We analyze the range in CDR volumes in AR6 WGIII pathways by exploring relationships between variables as potential driving forces, focusing on CDR in 2050 and scenario properties linked to reaching net-zero CO 2 . It is also shown how the relative and absolute contribution of CDR to total mitigation up until reaching net-zero CO 2 substantially differs across scenarios. The volumes of CDR in 2050 and 2100 and the cumulative amount throughout the 21 st century were most strongly correlated to the degree to which CO 2 emissions are reduced as a means of reaching net-zero CO 2 . CDR in 2050 is also substantially correlated to the timing of net-zero CO 2 . The robustness of the analyzed relationships was evaluated by comparing different scenario filtering and data-cleaning approaches. Beyond filtering and cleaning, additional factors that influence CDR deployment in scenarios, such as discount rates, carbon price trajectories, and scenario design choices, were discussed.