Open Sea Cages Research Articles

Design and Experimental Research of a Lifting-Type Tidal Energy Capture Device

In this study, in order to promote the development of far-reaching marine aquaculture equipment in an intelligent direction and solve the problems related to power supply, a tidal current energy harvesting device for a low-velocity sea area is proposed. For low-velocity waters in farming areas, the device can effectively harness tidal energy to provide a stable power supply to open sea cages. A mathematical model of the Savonius turbine blade is established, and the influence of the distance between the impeller center and the water surface on the energy capture efficiency of the turbine is analyzed through numerical simulation. Using ANSYS2021R1 software, the velocity field of the floating body is simulated, and the overall structure and anchoring system of the power generation device is designed. In order to verify the effectiveness of the power generation device, a test model is built and a physical model test is carried out. The variation in parameters related to the relative distance between the impeller and the water under different flow velocities is tested, and the test data are analyzed. The test results show that the floating body can increase the flow speed by 10%. Optimizing the blade number and order of the S-turbine can capture more than 20% of the energy. Under different flow velocities, the capture power of the impeller first increases and then decreases with increasing distance from the water. When the center of the impeller is one-quarter of the impeller diameter higher than the water surface, the output power of the impeller is at the maximum. This indicates that the proposed power generation device can effectively use tidal energy under different water depth conditions and provide a stable power supply for far-reaching marine aquaculture equipment.

Dietary Chlorogenic Acid Improved Muscle Quality, Antioxidant Capacity, and Pro‐Inflammatory Responses of Blackspotted Croaker Protonibea diacanthus

The widespread use of commercial feeds with high‐fat content in aquaculture may lead to oxidative stress and inflammation in fish during culture, which may cause changes in fish muscle texture. Therefore, mitigating oxidative stress and inflammation during fish farming holds paramount importance in improving fish muscle quality. In this study, we investigated the effect of different dietary levels of chlorogenic acid (CGA; 0, 100, 200, 400, 800, 1600 mg/kg diet, P1–P6) in commercial diets on the muscle of blackspotted croaker (Protonibea diacanthus) through an 8‐week feeding trial in open sea cages. The results showed that high dietary CGA levels (P5–P6) could significantly reduce muscle oxidative stress and inflammation (P < 0.05). Muscle toughness (hardness, chewiness, shear force, and gumminess) improved significantly as CGA levels increased (P < 0.05). It was also observed that the gap of muscle fiber was significantly reduced, while the muscle fiber density was significantly increased with the increase of CGA level (P < 0.05). Notably, dietary CGA also had a significant effect on collagen content in the muscle (P < 0.05), which may also be a crucial factor affecting muscle texture. Furthermore, it was found that the reduction of inflammation and increase of collagen deposition in muscle by dietary CGA may be related to the upregulation of transforming growth factor beta (TGF‐β) signaling pathway. Finally, it can be concluded that a dietary CGA supplementation of 1173.11 mg/kg is suggested for the aquaculture of P. diacanthus, based on the muscle texture quality.

An integrated techno-economic decision-support fiscal forecast model for sea cage mariculture enterprises for Asian seabass production in Indian territorial waters

Cage-based mariculture ventures in India are expanding, particularly emerging with the most sought-after candidate Asian seabass Lates calcarifer in territorial waters. However, comprehensive techno-economics have not been attempted, and thus hindering the sector's growth potential. To address this, a spatiotemporally validated decision-support model was developed to optimize investment decisions and forecast economic performance. Peer-reviewed contextual data was used to establish scientifically valid assumptions, and robust scenario simulations were conducted to benchmark production systems and species performance. Unit standards were defined and benchmarked for metric deployment for the first time. Capacity Utilization (CU) was found to be critical for success, achieving break-even at 31% CU with set model specifications derived from an inverse linkage with market price dynamics. The enterprise model demonstrated significant economic potential over a ten-year horizon, with low risk due to current policy initiatives by the Indian government. Furthermore, the model architecture and benchmarked specifications derived are adaptable to other candidates with its species-specific biological parameter application. The study can aid stakeholders in planning the enterprise budget. Most importantly, the study highlights the advantages of integrating technological, biological, and financial approaches to mitigate risks and promote the mariculture sector in India. The adaptability of the Asian seabass to farming systems, technical feasibility, and the availability of seeds and suitable sites along the Indian coast have been influential factors and these attributes in specific underpins the profitability. This research provides a way forward for the future of the sector in India, particularly with regard to farming of the Asian seabass, and emphasizes the importance of techno-economic models (TEM) in promoting strategic development of the mariculture sector through open sea cage farming.

Evaluation of black soldier fly larvae meal as a functional feed ingredient in Atlantic salmon (Salmo salar) under farm-like conditions

Atlantic salmon (Salmo salar) were fed diets containing black soldier fly larvae (BSFL) meal at two inclusion levels for 13 months in open sea-cages. BSFL meal replaced plant-based ingredients and dietary insect meal inclusion levels were at 5% and 10%. A commercial salmon diet was fed as a control diet. Fish were reared from ~173 g to ~ 4 kg and were randomly distributed into nine open sea-cages with ~6000 salmon/cage (12×12 m2; 1900 m3). Fish from the sea-cages were sampled at two time points (mid and final samplings) to study the dietary effects of BSFL meal on the general health and welfare. Monthly assessments of sea-lice and gill score were conducted to evaluate the overall well-being of the salmon. The findings from the current study revealed that dietary inclusion of BSFL meal up to 10% did not have any significant effects in general growth, welfare or survival. However, significant positive response was observed in the general skin mucosal, hematological, and gene expression profiles of salmon. Notably, the group of salmon fed with 5% BSFL meal showed a significant decrease in plasma aspartate transaminase and alanine transaminase. Also, a significantly higher expression of interleukin1β in both skin and gill along with upregulation of matrix metallopeptidase9 and mucin18 in gill were observed in salmon fed BSFL at 5%, which aided in increased immune responses. Apart from that, this group had significantly higher mucus secretions, decreased cortisol response and increased number of erythrocytes. Furthermore, the delousing stress had a significant effect on the plasma cortisol, and these responses were independent of the dietary effect. Moreover, these immune responses behaved differently at different fish size and time points, acknowledging the influence of various factors in immune modulation. Overall, the findings from this study showed the effects of dietary BSFL meal to modulate the immune status of salmon. This study aims to fill the existing knowledge gaps regarding the impact of incorporating BSFL meal as a functional feed ingredient into the salmon diet on health and immune status replicating real farm conditions.

Water Flow Requirements of Post-smolt Atlantic Salmon (Salmo salar L.) Reared in Intensive Seawater Flow-through Systems: A Physiological Perspective

Environmental challenges related to open sea cage production of Atlantic salmon have sparked interest in developing commercial-scale semi-closed sea systems for post-smolt Atlantic salmon (100–1000 g). Determining the mass-specific water flow required by post-smolts will largely influence the design and dimensioning of such systems. In this experiment, post-smolts were exposed to four levels of specific water flow: 0.2, 0.3, 0.4, and 0.5 L kg fish−1 min−1. All treatments involved flow-through seawater with full oxygenation, a salinity of 34‰, and a mean temperature of 9.3 °C. The stocking density was kept stable at 75 kg m−3. Water pH decreased with reduced flow, while partial pressure of carbon dioxide (pCO2) and total ammonia nitrogen (TAN) in the water increased. The increase in water CO2 was reflected in the blood with increased pCO2, HCO3−, and decreased Cl− in the lowest water flow treatment (0.2 L kg fish−1 min−1), indicating a typical regulatory response to increased water CO2 over the eight-week experimental period. No negative effects on osmoregulation, external macroscopic welfare, or performance indicators were observed, suggesting that within the time period of this experiment, post-smolts can compensate for reductions in water flow down to 0.2 L kg fish−1 min−1. However, to avoid activating and exhausting potentially energy-costly physiological regulatory mechanisms, it is suggested to keep specific water flow above 0.3 L kg fish−1 min−1 in large-scale operations with semi-closed sea systems at intermediate temperatures.

Real-time monitoring of cause-specific mortality- and losses in industrial salmon farming

Mortality represents a major challenge in farming of salmon in open sea cages. Production takes place in large cages with up to 200,000 fish and offers no other treatment of individual fish than euthanasia of moribund fish. Improvements need to take place as preventing future problems. The described project was initiated with the objective to develop a standardized system for classification of mortality and losses in aquaculture. The WHO's International Classification of Disease (ICD) has served as a model tool, with adaptation into an animal production system. The system is based on causality with the underlying cause of death as the principal variable to monitor. The system describes the fish-farmer as the primary user, and with additional opportunities for the supply industry, authorities, and research to utilize anonymized data. The classification system is organized with an alphanumeric code in a hierarchical structure with three levels: six main categories, causal subcategories at level 2, and in principle, unlimited underlying causes at level three. The hierarchy allow both registration and retraction of data at each of the three different levels. The proposed code is conceptuated to also allow classification of other losses than mortality, thus being able to monitor the effect of the underlying cause for all areas of losses, including quality downgrading, reduced growth, reduced feed conversions etc. A code covering all areas of losses will enable the fish farmer to monitor the total effect of underlying causes, both in biological and monetary terms. Through systematic monitoring it will be possible to target resources in the direction of losses with the highest impact and the interventions with the highest pay-back. By establishing a unique code, it will further be possible to standardize registrations between area of losses within a company, between companies and regions, and potentially also between countries.

In lumpfish We Trust? The Efficacy of Lumpfish Cyclopterus lumpus to Control Lepeophtheirus salmonis Infestations on Farmed Atlantic Salmon: A Review

In this review, we have systematized current knowledge about the effect of stocking lumpfish (Cyclopterus lumpus) as cleaner fish to control Lepeophtheirus salmonis infestations on farmed Atlantic salmon (Salmo salar L.). The review was prompted by recent reports in which the usefulness of lumpfish has been doubted, and the urgent need to investigate whether common lumpfish can be used to reduce L. salmonis numbers on farmed Atlantic salmon by active grazing on this species. Available published data clearly indicate that lumpfish graze on L. salmonis, and can significantly lower the lice burden in Atlantic salmon farming. It is possible to enhance the lice grazing behavior of lumpfish with the assistance of live feed conditioning prior to sea pen transfer, and with selective breeding. Data indicate that lice grazing of lumpfish is size dependent, and grazing effect is low for lumpfish larger than 200–250 g. Observations from large-scale rearing of Atlantic salmon in open sea cages in Norway, Iceland, the Faroe Islands, and Scotland also indicate that lumpfish can be effective in lowering infestations of L. salmonis on salmon. Overall, this present review reveals that lumpfish can actively contribute to lower numbers of L. salmonis on farmed Atlantic salmon.

Investigation of growth performance of post‐smolt Atlantic salmon ( Salmo salar L.) in semi closed containment system: A big‐scale benchmark study

The Norwegian salmon industry faces challenges related to sea lice (Lepeophtheirus salmonis) infestations, escapees, diseases and environmental impact. Semi-closed containment systems (S-CCS) have been proposed to abate these challenges. In the S-CCS, cultured fish are separated from the natural environment by a physical barrier, reducing the time fish spend in open sea cages. Production data from six cohorts of salmon were used to compare growth and performance of fish raised in S-CCS and in open sea cages (control group) incorporating different seasons. The study was carried out in two phases. Phase one used post-smolts from approximately 100 to 800 g in seawater, and fish in S-CCS were compared with a reference group from an open sea cage. The second, grow-out phase covered the size range from approximately 800 to 5000 g in open sea cages; here fish previously reared in S-CCS were compared with fish from a control group. The study showed a significantly lower infestation of sea lice in S-CCS (0.02–0.04) fish compared with the control group (0.18–0.62) during the post-smolt phase. Furthermore, in the grow-out phase the S-CCS group showed higher growth rate and higher final weight (4680 g [spring], 4890 g [fall]) for the S-CCS group compared with the control group (3800 g [spring] and 4080 g [fall]). Salmon raised in S-CCS showed significantly higher survival compared with the control group in open pens, indicating increased resilience in fish raised in S-CCS when transferred to open net pens in sea. It is concluded that S-CCS have advantages compared with exposure to the natural environment in open pens in western Norway.

Design of water surface collection robot based on deep sea cage culture

At present, the collection of floating garbage such as dead fish in deep and far sea cage culture waters mainly depends on manpower, which is not only difficult and inefficient, but also has great potential safety hazards. In order to solve the above problems, a water surface collection robot based on marine cage culture is designed and developed. The dead fish on the water surface are collected through the joint action of propeller and forearm drainage and retraction device. At the same time, the relevant performance indexes of the designed water surface collection robot are verified by making the prototype and water surface collection experiments, which meets the needs of simple and efficient collection and cleaning of dead fish in deep and open sea cage culture, so as to provide a reference basis for the practical application of the collection robot.

Socio-economic elevation through open sea cage farming-Evidence from Mandapam region of Tamil Nadu, India

Cage culture guarantees the multiplication of seafood output and revenue generation from a small unit area when compared to significant capital investment oriented onshore farming technologies. The Mandapam Centre for Sustainable Aquaculture (MCeSA) of Tamil Nadu Dr. J. Jayalalithaa Fisheries University (TNJFU) through the cage culture demonstration as part of the NFDB-funded project ‘Open Sea Cage Culture of Marine Finfishes along the Coast of Ramanathapuram District in Tamil Nadu’ is continuously involved in disseminating this valuable technology which provides higher yield and income to meet the alternative livelihood needs and to uplift the socioeconomic conditions of the coastal fisherfolk in Ramanathapuram District, Tamil Nadu. Case studies were undertaken in the region to assess the impact of MCeSA and a success story of Mr. V. Nagadas, one of the NFDB scheme beneficiaries is shared here who has implemented the cage culture of lobster and earned a total profit of 280000 INR. The farmer's success and the MCeSA's technical guidance and support are now inspiring other fishermen to adopt the farming.

Testing of new sampling methods and estimation of size structure of sea bass (Dicentrarchus labrax) in aquaculture farms using horizontal hydroacoustics

In aquaculture, monitoring fish size and density is fundamental to improve management and profitability of fish farms. The aim of this study is to test whether horizontally aimed 200-kHz transducers are adequate to obtain fish size structure in open-sea cages in order to apply horizontal hydroacoustics as a non-intrusive and innovative technique in sea bass (Dicentrarchus labrax) farming. Several sampling strategies have been tested by placing the transducer in two different positions: outside the cage and inside the cage. In addition, two sampling approaches have been implemented: placing the transducer at a fixed position or moving it vertically.The results show that horizontal hydroacoustics is a useful technique for monitoring size distribution of sea bass in farming cages. The most adequate sampling method consists of using a vertically moving transducer positioned outside the cage, since it exhibits the narrowest size distributions with the lowest variance estimates, which matches the data provided by fish farmers.

Community-Based Cobia, Rachycentron canadum (Linnaeus, 1766) Culture in Open Sea Cages at Olaikuda, Pamban Island, India: An Economic Analysis of Technology Transfer Initiative

The Olaikuda Village of Pamban Island was chosen to demonstrate and transfer the open sea cage culture technology of cobia by the National Institute of Ocean Technology (NIOT). Olaikuda is a fishing hamlet with 1,000 traditional fishers who are primarily involved in trap fishing. An attempt was made to supplement their income under the societal development initiative of the NIOT. With the active participation of the local fishers of Olaikuda, 3,000 hatcheryproduced cobia, Rachycentron canadum (Linnaeus, 1766) fingerlings were stocked equally in two cages with a stocking density of 4.7 fingerlings.m-3 . The cobia stocked in sea cages were reared with the locally available low-value fishes for 8 months. The sea farmed cobia attained an average weight of 3.3 kg resulting in an average daily growth rate of 13.5 g with a survival rate of 75 %. The fish were harvested on the 245th day of culture, which yielded 7,000 kg of marketable size cobia fish (1st cage 3,687 kg and 2nd cage 3,313 kg with an FCR of 1:5.5). The harvested fish were sold at the farm gate price of USD4.42 kg-1 , fetched USD30911.84. The economic analysis revealed a profit margin of USD1.26 kg-1 . The parameters such as cost of production, productivity, profitability, socio-economic impacts of native fishers were analysed during the study. The result of this farmer-driven attempt is encouraging the farmers across the coastal states to do cage culture farming in a big way. Similar efforts in more organised massive programs will create new jobs and reduce the fishing pressure on the natural sea stocks and considered a viable alternative livelihood for the fishers’ community affected by the declining natural fishery resources and international border issues.

Comparative assessment of fish assemblages around open sea cages vis-a-vis common fishing ground

Comparative assessment of fish assemblages around open sea cages vis-a-vis common fishing ground

Condition Index, Meat Yield and Biochemical Composition of Mediterranean Mussel (Mytilus Galloprovincialis Lamarck, 1819) from Canakkale Strait, Turkey

The present study was performed in Çanakkale Strait from September 2012 to August 2013. Biochemical composition (protein, total lipid, moisture, and ash), condition index, and meat yield of Mediterranean mussel, Mytilus galloprovincialis in the net systems hung out the open sea cage units monthly. The mean condition index and meat yield of M. galloprovincialis were found 8.12±0.48 and 16.07±0.70%, respectively. A positive correlation was found between condition index and protein, carbohydrate, and meat yield whereas a negative correlation was seen between condition index and weight, length, lipid, moisture, and ash. In terms of seasons, condition index and protein values were high in autumn, lipid values in summer, and carbohydrate values in spring.

Short term culture of wild caught juvenile rabbit fishes (Siganus javus) in open sea cages at Palk Bay

Objectives: The main objective of the study was to collect and rear the unmarketable, small sized S.javus which is mostly rejected by the traditional fisherman. During fishing activities, under sized S.javus ranging in sizes from 25 to 40 kg (< 30-40 % of total catch/day) is being captured. Due to very low marketable value these small fishes (<250 g) get rejected. Therefore, we utilized this as an economically viable option for utilization as seeds for rearing until they reach the necessary marketable size. Methods: Undersized juveniles (12-16 cm, 40 -55 g) were collected from nearby Olaikuda village,Rameshwaram using traditional traps made using bamboo and odai tree bark (Acacia planifrons). The collected juveniles were stocked in sea cages and fed with locally formulated plant based feed containing 28-32 % crude protein. Findings: Harvesting was successfully done after 140 days with 90 % survival. The average growth rate achieved was 2.5 g /day with FCR of 2.01. This resulted in an average harvest size of 400 g/fish from its initial stoking size of 50 g with an attracted market value of Rs. 150/kg. Novelty: Till date, no attempts were made to commercialize such harvesting techniques for the species Siganus javus in pilot scale in India (Except James, 1984). Keywords: Rabbit fish; Siganus javus; sea cage culture; rabbit fish culture; Siganidae

A Study on Ecological Succession of Macrofouling Communities in Sea Cage Farm in South-West Coast of India

Development of aquaculture facilities like cages has led to rise in submerged structures which provide ample substratum to biofoulers which could greatly interfere with culture operations. An attempt was made to study the biofouling communities and succession of macro foulers on the cage culture net installed in the open sea. The main objective of the present study is to reveal the succession pattern of the biofouling communities on the panels of cage culture sites to find out seasonal settlement pattern, Dominant species and Climax community. A long-term study on the succession pattern of the cage farm experimental-net-panels revealed results as Hydroids-Gastropods-Hydroids-Barnacles-Modiolus-Green mussels. Hydroids were initial communities on the net panels and green mussels (Perna viridis) formed the climax community, also dominating on the cage culture nets. Different succession patterns were observed in two sites as well as in culture nets studied. The net panels of the cage were loaded with hydroids in the initial months and the peak fouling was during May. So frequent net cleaning was required during summer and during the spat settlement period of green mussel (September, October and November). Modiolus settlement during February month on the culture nets can be avoided by net exchange immediately after spat fall in this month. This attempt was made to study the ecological succession on the panels, in cages installed in Karwar, which is the first attempt, since the open sea cage culture was initiated in India. Looking at vast opportunities for further development in biofouling research, the aim of this investigations was to obtain the baseline information about the ecological succession pattern of biofouling organisms in fish cage sites. More research on biofouling in mariculture is essential to ensure the profitability of the aquaculture operations with environmental safety measures as a prime criteria

Acoustic density estimation of dense fish shoals

Multiple scattering of acoustic waves offers a noninvasive method for density estimation of a dense shoal of fish where traditional techniques such as echo-counting or echo-integration fail. Through acoustic experiments with a multi-beam sonar system in open sea cages, multiple scattering of sound in a fish shoal, and, in particular, the coherent backscattering effect, can be observed and interpreted quantitatively. Furthermore, a volumetric scan of the fish shoal allows isolation of a few individual fish from which target strength estimations are possible. The combination of those two methods allows for fish density estimation in the challenging case of dense shoals.

Multiscale modelling of cage effects on the transport of effluents from open aquaculture systems.

Most Atlantic salmon mariculture operations use open sea cages for the grow out phase. The ultimate fate and effects of the effluents and the possibilities of disease transfer between fish farms are major concerns for farmers, governance and the general public alike. Numerical model systems applied to studying and managing effluents and disease transfer in mariculture must realistically resolve the hydrodynamics in the vicinity of the fish farms. In the present study, the effects of the aquaculture structures on the current patterns were introduced in the ocean model system SINMOD. The drag parameters for the ocean model were determined by comparing the simulation results from the ANSYS Fluent ® software suite and SINMOD in an idealized channel setting with uniform currents. The model was run for a number of realistic scenarios in high horizontal resolution (∼30 m) with sea cages influencing the flow field. Comparisons between extensive current measurements and the simulation results showed that the model system reproduced the current local current field well. By running simulation scenarios with and without the effects of the sea cages on the flow field, it was possible to assess the importance of such effects for numerical dispersal models and aquaculture environment interactions simulations and hence for assessment of environmental impacts.

Genetic variation in growth pattern within a population of farmed Atlantic salmon (Salmo salar) during a standard production cycle

Selection for faster growth to market size has a long history in selective breeding programs for aquaculture species. In Atlantic salmon, selection for faster growth has been carried out for more than four decades, i.e. about ten generations. Genetic improvement of growth rate is indicated as favourable correlated to improved feed utilization and, from an economic perspective, it can be argued that improved feed utilization is the main breeding objective: improved fish production per unit of nutrients (protein or energy) provided. However, also reduced production time in challenging grow-out environments, i.e. reduced exposure to sea lice and other disease agents, may be highly valuable from an animal welfare and environmental perspective. Reduced production time in challenging grow-out environments may also be economically favourable by reducing the need for mechanical or chemical treatments of the fish.Body weights at stocking and harvest are commonly recorded in breeding programs for Atlantic salmon. Selection for faster growth rate is usually based on recorded harvest weights, which represent the accumulated growth during the entire production cycle. Alternatively, selection could be based on other growth parameters, i.e. Thermal Growth Coefficient (TGC), which specify growth in specific production periods. Production of Atlantic salmon in open sea cages entails large variation of environmental parameters, i.e. water temperature, water quality, salinity, day light etc., that influences the growth.In this study, growth of individual Atlantic salmon in an open sea cage were investigated (as a part of the project BEHAVEGENES, NFR 2014–2017) to describe potential GxE for growth in different production periods. Test fish were transported to sea in autumn, 8 months after first feeding, and harvested after 16 months at a mean harvest weight of 5.5 kg. Individual body weights were recorded at five different time points allowing estimation of growth during a total of four subsequent production periods. Sexual growth dimorphism was discovered well before onset of sexual maturation; already 4 months after sea transfer, at average population body weight ~500 g, males were measured on average 2.8% heavier than females. Heritability estimates for body weight were all high (0.42–0.72), while heritability estimates expressed by growth calculated as TGC were mediate to high (0.35–0.56). Genetic correlations between growth (TGC) in different production periods varied between −0.20 and 0.82. The correlation between growth during an 8-month summer period (average body weights increase from 500 g to 3.9 kg) and a 4.5-month winter period (average body weight increased from 3.9 kg to 5.8 kg) was not significant (rg 0.16 ± 0.17), suggesting genetic variation for growth pattern and that different genes are involved in different growth periods.

Mesocopic wave physics in a dense fish school

Multiple scattering phenomena of acoustic waves are studied in a dense school of fish. A 3-D multibeam sonar is used to probe the backscattered intensity from a dense school fish contained in an open sea cage. The signature of wave interferences in this mesoscopic and quasi-natural media is shown by measuring coherent backscattering (CBE) effects. In particular, the static and time-resolved measurements of the CBE profile provide estimations of transport parameters such as the transport mean free path l* and the energy velocity of diffusive waves ve . It turns out that fish can scatter sound very strongly, allowing one to achieve a transport mean free path comparable with the wavelength of ultrasound. In this case, traditional fisheries acoustics methods are compromised by multiple scattering effects. Thus, this new approach could help to overcome issues encountered in aquaculture to evaluate the total biomass of dense schools of fish.