Fish Cages Research Articles

Environmental impacts of tilapia fish cage aquaculture on water physico-chemical parameters of Lake Kivu, Democratic Republic of the Congo

In Africa, cage aquaculture has been growing due to its potential to address food insecurity concerns, provide livelihoods, and contribute to local economies. However, there is a need for continued research on the sustainability and potential ecological effects of cage aquaculture in African lakes and reservoirs. Even with an adequate amount of water, lakes and reservoirs cannot provide ecosystem services if their water quality is not properly managed. The current study on Lake Kivu, DRC focuses on understanding the effects of tilapia cage aquaculture on selected water quality physico-chemical parameters in the Bukavu sub-basin, DRC. The research was conducted in both caged and uncaged sampling stations, on the spatial and temporal scale from April to September 2023 at three bays serving as sampling stations: two caged (Ndendere, Honga) and one non-caged (Nyofu). Some physico-chemical parameters were measured in situ, whereas chlorophyll a and nutrients analysis were performed at the Institut Supérieur Pédagogique (I.S.P) laboratory in Bukavu. The parameters were used to calculate three indices water quality indices: the water quality index (WQI) to classify the water quality at the stations, the organic pollution index (OPI) to determine the level of organic pollution, the Carlson's Trophic Status Index (CTSI) to classify the trophic state of the stations. Chlorophyll a concentration was a measure of algal biomass. All physico-chemical parameters, apart from DO, ammonium and temperature showed no significant differences among stations and depths. Interaction between stations and between seasons was only observed on turbidity. The WQI for all the sampling stations ranged from medium to good quality (51–90). The OPI for all stations showed minimal level of pollution (4.6–5.0) hence lake's water still organically unpolluted. CTSI results indicated the sampling stations are in a eutrophic state (50 to 70). Fish cage aquaculture does not yet pose harm to the water quality of the two Lake Kivu stations under consideration, according to the study's findings. However with the anticipated growth of cage fish farming activities to meet the rising fish demand, continuous monitoring of water quality in the Lake should be done to inform management decisions and for sustainable aquaculture.

Design and Dynamic Analysis of a Co-Existence Solution Between a Semi-Submersible Offshore Fish Cage and a Spar-Type Floating Offshore Wind Turbine

Abstract Clean energy captured by offshore wind turbines has been widely used for supporting onshore activities. In the near future, facilities such as offshore wind turbines can also play an important role in the energy transition of offshore activities. Offshore wind energy can be employed for electrifying operations in offshore fish farms, which are traditionally supplied by diesel-engine barges/generators. Based on this motivation, this study focuses on the design of a shared mooring system between a semi-submersible offshore fish cage and a spar-type floating wind turbine. A numerical model of the proposed shared mooring system is implemented in a global response analysis software sima for performing fully coupled time-domain simulations. The configuration of the shared mooring line is determined using an engineering approach, which comprises Irvine’s formulation, system eigenvalue analysis, and cost estimation. Moreover, relevant case studies by altering the environmental conditions are performed. Extreme operational conditions that may give large relative motions are investigated thoroughly. The dynamic performance of the integrated system is compared with that of individual structures. The global motion of the floating wind turbine and its mooring line’s tension behavior are obviously influenced by the existence of the shared line. In general, the present work investigates the feasibility of a shared mooring system for these types of offshore structures and further gives insights into the engineering design procedure.

Determinants of knowledge, attitude and perception towards cage fish farming technologies among smallholder farmers in Uganda

Determinants of knowledge, attitude and perception towards cage fish farming technologies among smallholder farmers in Uganda

Uncertainty Assessment of the Remaining Volume of an Offshore Gravity Fish Cage

The volume of a gravity cage is greatly reduced under a current due to the flexible structure, which affects the growth and health of the fish. Thus, an accurate assessment of cage volume is essential to determine the number of fishes in the cage. In this study, firstly, a numerical model was built to study the cage volume reduction of gravity cages due to the flexible net deformation when subjected to uniform flow. The remaining volume was calculated and compared with earlier experiments. Even though the flow velocity reductions were considered according to the data from previous experiments, the differences between the results from the numerical calculation and the towing tests are still significant. The physical model tests were treated as the reference value to investigate the uncertainty of the model results. Both the velocity-independent model error and velocity-dependent model error were calculated. With the help of the error models, the uncertainty of the remaining volume can be predicted. In addition, the velocity-dependent model error performs better in evaluating the uncertainty of the numerical calculation of the remaining culturing volume. Overall, the results show that the numerical model assisted by the model errors can calculate the cage volume accurately.

Fluid–Structure Interactions of Net Cages—Full-Scale Pushing Tests in the Field

Abstract This paper presents field tests on a full-scale cage, with and without fish, being pushed by a boat in Masfjorden at various speeds. The purpose was to imitate the exposure of net cages to different currents. The tests involved measuring cage deformations, fish behaviors, and the corresponding flow upstream, downstream, and inside the cage. The study found that the experimental setup used can achieve predictable and stable upstream flow for a full-scale net cage. Based on pressure tag data, the volume reductions of the cage, both with and without fish, were estimated at different speeds. Both cases show a similar trend of cage volume reduction with respect to flow speeds as the previous studies. Moreover, the presence of fish had limited the influence on the net volume change. The reduction in speed inside and downstream from the cage was within the range reported in previous literature. Notably, when the cage becomes significantly deformed, it not only reduces flow speed but also alters flow directions, as evidenced by the high variability of flow direction inside the empty cage, particularly at high speeds. The measured flow speed inside the stocked cage also exhibited high variability, but the pattern of variation differed significantly from that of the empty cage, indicating the influence of fish. These findings suggest that traditional flow speed models might oversimplify the flow field in and around fish cages, especially in studies concerning the dispersion of particles, pathogens, and dissolved matter in and out of fish cages.

Perceptions of the attributes of fish farming in floating cages on Lake Toho in southern Benin: the case of fishermen

Fishing is an economic activity that generates significant added value, contributes to job creation and improved food and nutritional security. For several years however, it has been confronted for several years with a decline in halieutic resources in the face of which fish farming in floating cages constitutes an optimal management solution. The objective of this article is to analyze the perceptions of the attributes of fish farming in floating cages by fishermen. The study involved a random selection of 210 fishermen from the three municipalities (Lokossa, Houéyogbé and Athiémé) of Toho lake. Analyzes of variance and correlation followed by principal component analysis were used to analyze the data. The results showed that there are three groups of fishers with different perceptions of floating cage fish farming. Fishers who perceived fish farming in floating cages as a form of fish farming that is efficient and very demanding but less suitable in the long term represent the first group. For the second group of fishermen, there are markets for the sale and sale of fish reared in floating cages, but there is difficulty in finding inputs (provend, veterinary products and antibiotics) of fish in floating cages. The third group perceived that fish farming in floating cages is a very flexible, rigid and efficient activity compared to other fish farming techniques. According to this study, it is important that the Government of Benin take into account the perceptions of fishermen before installing floating cages on Lake Toho.

Developments in Modeling Techniques for Reliability Design of Aquaculture Cages: A Review

Offshore aquaculture is gaining traction due to space limitations in nearshore waters, more pristine water, cooler temperatures, and better waste dispersal. This move has spurred the development of new technologies for offshore aquaculture. Despite the numerous analysis methods for designing aquaculture infrastructure, limitations and challenges remain in modeling the influence of fish cages on flow fields and in addressing fluid–structure interaction. This paper presents a comprehensive review of analysis methods and modeling techniques applied in the design of offshore aquaculture systems, emphasizing the structural reliability analysis. This review includes statistical and predictive analysis of extreme sea conditions, evaluation of environmental loads and hydrodynamic analysis, structural reliability modeling and assessment, and seabed geotechnical responses to mooring anchors. For each design consideration, the relevant theories and applicability are elaborated upon and discussed. This review provides valuable insights for engineers involved in the development and design of offshore aquaculture infrastructure.

In field use of water samples for genomic surveillance of infectious spleen and kidney necrosis virus (ISKNV) infecting tilapia fish in Lake Volta, Ghana.

Viral outbreaks are a constant threat to aquaculture, limiting production for better global food security. A lack of diagnostic testing and monitoring in resource-limited areas hinders the capacity to respond rapidly to disease outbreaks and to prevent viral pathogens becoming endemic in fisheries productive waters. Recent developments in diagnostic testing for emerging viruses, however, offers a solution for rapid in situ monitoring of viral outbreaks. Genomic epidemiology has furthermore proven highly effective in detecting viral mutations involved in pathogenesis and assisting in resolving chains of transmission. Here, we demonstrate the application of an in-field epidemiological tool kit to track viral outbreaks in aquaculture on farms with reduced access to diagnostic labs, and with non-destructive sampling. Inspired by the "lab in a suitcase" approach used for genomic surveillance of human viral pathogens and wastewater monitoring of COVID19, we evaluated the feasibility of real-time genome sequencing surveillance of the fish pathogen, Infectious spleen and kidney necrosis virus (ISKNV) in Lake Volta. Viral fractions from water samples collected from cages holding Nile tilapia (Oreochromis niloticus) with suspected ongoing ISKNV infections were concentrated and used as a template for whole genome sequencing, using a previously developed tiled PCR method for ISKNV. Mutations in ISKNV in samples collected from the water surrounding the cages matched those collected from infected caged fish, illustrating that water samples can be used for detecting predominant ISKNV variants in an ongoing outbreak. This approach allows for the detection of ISKNV and tracking of the dynamics of variant frequencies, and may thus assist in guiding control measures for the rapid isolation and quarantine of infected farms and facilities.

Multistakeholder partnership in implementing cage fish culture as a livelihood venture for rural youth: A case study in Kerala State, south India

Rural development is a process of implementing location-specific sustainable modelsutilising ecosystem services with participation of local people. Ezhikkara is a coastalvillage surrounded by brackishwater creeks and Pokkali paddy-shrimp fields located inParavur Taluk of Ernakulam District, Kerala, south India. To address the employment issuesamong rural youth, Ernakulam Krishi Vigyan Kendra (KVK) of ICAR-Central Marine FisheriesResearch Institute (ICAR-CMFRI), initiated cage fish culture in the Veerampuzha public waterbody in association with Pallikkal Service Cooperative Bank (PSCB). Local youth were trainedin the technical aspects of cage fish culture and the bank provided financial support forimplementing cage fish farming. The fish produced were marketed directly to the customersthrough farmgate markets. Farmers sold live fish directly at the farm gate by attractingconsumers through advertisements floated by the KVK. They were sufficiently educated tofix uniform pricing to avoid farmer-farmer competition in direct marketing. An online fishdelivery mechanism by pre-bookings through a mobile application was also established.The cage fish culture got wide acceptance among the rural youth as an alternate incomesource. The main challenges faced during the implementation of cage fish culture wasthe presence of invasive black mussel (Mytella strigata), annual flooding and the massiveaccumulation of weed plant Eichhornia crassipes. This experience unravels the requirementof continuous technical backstopping for marginalised communities to successfullyimplement technology-based farming models as alternate livelihood sources. Keywords:Asian seabass, Aquaculture, Cage fish culture, Live fish, Marketing

Effects of fenobucarb based-Excel Basa 50EC on brain cholinesterase of juvenile snakehead fish (Channa striata) in the Vietnamese Mekong Delta's rice fields.

Fenobucarb is one of most common insecticides applied to rice crops in the Vietnamese Mekong Delta. Paddy fields are preferred habitats for snakehead fish (Channa striata). Therefore, the probability of exposure risks and growth effects is highly. This paper aimed to examine the effects of using fenobucarb based - Excel Basa 50EC on the brain cholinesterase (ChE) of snakehead fish. Two rice fields, in which a single dose of Excel Basa 50EC was applied to one field, whilst the other acted as a control. Each field was subdivided into three plots by earthen dikes. In each plot, one fish cage (1.2 m x 1.2 m x 1.2 m) was installed that was stocked with 20 snakehead fish. The Excel Basa 50EC was applied once at the indication dose. The results highlighted that the concentration of fenobucarb in water at 1 hr after application was 116.72 ppb ± 12.64, which decreased to 23.96 ± 6.61 ppb after d and then to below detection limits (0.02 ppb). For fish living in this field, no mortality was seen, but ChE was significantly inhibited for 31 % on the first day and recovery following 7 days of exposure. Residues of fenobucarb in soil and fish should also be investigated furthermore.

Insights into ecological effects of fish and shellfish mariculture on microeukaryotic community

To better understand the ecological effects of mariculture, the diversity distribution, determinant and interaction of microeukaryote communities from fish cage and suspended shellfish farming were investigated in three bays of South China Coast. Our alpha and beta diversity analyses showed that the difference of the microeukaryote community between fish and shellfish farming was more significant at local than regional scale, and microeukaryotes respond more to spatial effect than mariculture effect at regional scale. Mantel test, variation partitioning analysis and co-occurrence network analysis revealed that the environmental factors especially chemical and biotic factors contributed more to community assembly in fish than shellfish farming. Based on the comparisons of community composition and determinant between fish and shellfish farming, the effect mechanisms of the two farming types on microeukaryote community were proposed. Fish farming brings significant environmental variation and thus has strong bottom-up impacts on microeukaryotes, while shellfish farming exerts a grazing pressure on microeukaryotes by filter-feeding and has top-down control to them. Furthermore, the network stability analyses revealed weaker community stability in fish than shellfish farming, suggesting that the microeukaryote community was more sensitive to environmental change deduced by fish than shellfish farming. Overall, this study revealed the different influencing mechanisms of fish and shellfish mariculture on microeukaryotes, which will improve the understanding of the ecological effects of mariculture and provide guidance for the management of mariculture under future environmental pressures.

Kajian kualitas air dan strategi pengelolaan Rawa Jombor, Klaten, Jawa Tengah

Rawa Jombor is a semiartificial reservoir whose contruction are works for serving the needs of irrigation in the dry season and as a floading control in the rainy season. Rawa Jombor also used for fish farming and floating restaurant by the community. The existence of the cages and floating restaurant can have a negative impact to the aquatic environment due to the disposal of waste and leftover food and metabolism that is deposited at the bottom of the water. This study aims to analyze the water quality, pollution levels and to develop a management strategy of Rawa Jombor. Water quality is measured at 9 sampling point determined by purposive sampling based on the use of Rawa Jombor. Pollution level is analized uses pollution index and the management strategy uses analytical Herarchy Process. The results show that Rawa Jombor has decreased water quality marked by several parameters that do not meet the class III of water quality standards according to Government Regulation No. 82 of 2001. Rawa Jombor is included in the category of mildly polluted in areas without activity, floating restaurant and fish cage for water allotment class I, II, III and IV with an average pollution index ranging from 1,02 to 2,886. To maintain the continuity of the Rawa Jombor, a management strategy with priority on the economic aspects is needed with the development of the Rawa Jombor for sustainable fisheries.

Numerical study on the lifting operation of a gravity-type fish cage

The dynamic behaviours of the lifting operation of a gravity-type fish cage under calm sea conditions are investigated in this study using an extended position-based dynamics (XPBD) method to obtain the structural deformations of the aquaculture nets. The original XPBD is improved to accurately predict the tensions of the aquaculture nets by applying correction forces. The present XPBD is validated by comparing the experimental results of a flexible horizontal net. The time-step sensitivity is verified for the case of the lifting operation of the fish cage. Results show that the lifting force increases rapidly resulting from the weight of the sinkers at the bottom of the side net. The maximum tension of the net is located at the net ropes connected to the centre point of the bottom net. The structure of the bottom net should be enhanced for safety lifting operations.

Operation And Maintenance Of Cengklik Reservoir In Supporting Integrated Water Resources Management

The management of the Cengklik Reservoir area which currently still has the main function as an irrigation facility with an area of 1,578 ha is still in the feasible category to be developed as a means of tourism and sustainable aquaculture. The development of the Cengklik Reservoir area in 2022 has entered the stage of developing supporting infrastructure such as a jogging track area, reservoir guardrails, arrangement of fish cage cultivation areas, and other infrastructure developments. This must also be balanced with a good pattern of management of operation and maintenance (OP) activities in the form of documents prepared by referring to the Reservoir Operation and Maintenance (OP) Guidelines. The method used in this research is simulation and evaluation on hydrological analysis using a flood design of 476.40 m3/s and an average flood water level of +142.64 m. The data used to measure the management of water resources in the Cengklik Reservoir is based on data hydrology, inflow, and outflow of the Cengklik Reservoir from 2010-2021 based on observations from the Bengawan Solo River Basin Center (BBWS). According to the evaluation results with measured parameters, it was found that the pattern of operation and maintenance of the Cengklik Reservoir is in the feasible category with the need for funding for the operation and maintenance of the reservoir of IDR 474,397,817.00 So that the integrated water resources development that has been carried out in the Cengklik Reservoir can be replicated in the reservoir others throughout Indonesia.

A Diversity of Copepods in Gajah Mungkur in Wonogiri Regency, Central Java, Indonesia

GajahMungkur Reservoir is a freshwater ecosystem thatis located6kmsouthofWonogiri Regency,CentralJavaProvince. Zooplankton is the primary consumer in the food chain of aquatic ecosystems. One of the common zooplankton found in freshwater ecosystem is copepod. Copepod is sensitive organism and play an important role as bioindicatator of water quality. The aimed of this study was to investigate the copepods diversity in Gajah Mungkur Reservoir. The method applied to this study is exploration and application of purposive sampling techniques in sampling. Copepods were collected from three different station, namely Station 1 (fishing area), Station 2 (tourism area), and Station 3 (fish cage area or keramba). The abiotic parameters were found to be varied on each station. Results showed that Gajah Mungkur Reservoir has moderately diverse copepods species with the average of diversity index 1.21. There were 7 species of copepods found in Gajah Mungkur Reservoir which mostly dominated by Mesocyclops sp., especially in Station 1 (fishing area). Meanwhile Microcyclops sp. was only found in Station 3 (fish cage area or keramba), suggesting that this species has a potential as bioindicator in Gajah Mungkur Reservoir. This study suggest that changes in physicochemical parameters might influence the diversity and abundance of copepod in Gajah Mungkur Reservoir.

Pollutant bioaccumulation in sentinel fish chronically exposed in Iguaçu river reservoirs (Southern Brazil) and human health risk of fish consumption

Bioaccumulation studies in fish mark the initial phase of assessing the risk of chemical exposure to biota and human populations. The Iguaçu River boasting a diverse endemic ichthyofauna, is grappling with the repercussions of human activities. This study delved into the bioaccumulation of micropollutants, the early-warning effects on Rhamdia quelen and Oreochomis niloticus in the Segredo Reservoir (HRS) and the potential risk of human exposure. Two groups of caged fish in three sites of the reservoir were exposed during the autumn-winter and spring-summer, while a third group (O. niloticus) underwent a twelve-month exposure, and inorganic and organic chemicals analysis in water, sediment, and biota. Additionally, metallothionein expression and genotoxicity were employed as biomarkers. PAHs, PCBs, Al, Cu, Fe, and As in water and DDTs, Cu, Zn, and As in sediment surpassed the thresholds set by Brazilian regulations, where DDT exhibited bioaccumulation in muscle, alongside metals in liver, kidney, gills, and muscle tissues. R. quelen showed metallothionein expression whereas DNA damage and NMA frequencies were elevated in target organs and in brain and erythrocytes of O. niloticus during summer. In this species the DNA damage in liver was remarkable after twelve months. Target Hazard Quotients and Cancer Risk values shedding light on the vulnerability of both children and adults. The reservoir's conditions led to heightened sensitivity to micropollutants for R. quelen species. The data presented herein provides decision-makers with pertinent insights to facilitate effective management and conservation initiatives within the Iguaçu Basin.

A semi-analytical model of an array of moored floating flexible offshore net cages under current loads

An analytical model of an array of moored floating flexible net cage systems is developed to study the dynamics and wave loads on the net cages under the linear water wave theory and small-amplitude wave response assumption. The Fourier–Bessel series expansion of the velocity potential is derived for the regions enclosed under the open-water and cage systems and their proximity. The theoretical solution is obtained by employing the least squares approximation method along with matching the velocity and pressure at the fluid-structure interfaces. The present result of horizontal displacement and horizontal wave load are compared with a published finite element analysis and with experimental data sets, respectively. Further, the results of cage displacements, cage accelerations, and wave loads on the different arrangements for mooring stiffness, cage radius, cage heights, and current speeds are compared and analysed. Moreover, the present analysis will be helpful to understand designing further a multiple floating fish cage system with flexible floaters application to offshore aquaculture.

Use of GIS‐based multicriteria evaluation for improved selection of suitable sites for cage fish farming in Mwanza Gulf, Lake Victoria

AbstractStagnating capture fisheries and increasing fish protein demand necessitate aquaculture production to bridge the gap. Lake Victoria is a potential water body for increasing fish production through cage farming. The sustainability of Lake Victoria for cage farming depends on timely and holistic site selection. However, current site selection methods involve complex, resource‐intensive field surveys that lack a holistic approach to integrate multiple factors. Accordingly, information regarding suitable sites for sustainable fish cage farming in Lake Victoria remains scarce. In this study, a transparent geographic information systems (GIS) and multicriteria evaluation (MCE) here after reffered to as GIS‐MCE was used to reveal potential sites to be permitted or avoided during cage aquaculture development in the Mwanza Gulf of Lake Victoria (Tanzania). Our analysis involved weighting and integration of sub‐models representing ecologically sensitive areas, physical environment, and socio‐economic and water quality variables into a single spatial model portraying different site suitability levels in the Mwanza Gulf. The results indicated that the sub‐models identified relatively larger suitable and most suitable sites compared to the overall model. No site maintained its status across all sub‐models. The overall model designated a small area (5.10 km2 or 1.52%) as the most suitable site, with 24.20 km2 (7.44%) as suitable, 64.47 km2 (19.82%) as less suitable, and 42.63 km2 (13.12%) as unsuitable for cage fish farming. The remaining area (188.84 km2 or 58.06%) was a constrained site to be avoided during cage aquaculture development. Taken together, the individual sub‐models are ineffective in designating potential sites for fish cage culture and thus should not be used solely. The GIS‐MCE general model provides a fast and timely method for identifying potential sites for cage farming in Lake Victoria. Fish farmers and managers should use the GIS‐MCE overall model in inland waters to facilitate site selection for complying with licensing requirements and decrease field extensive surveys.

Enhancing the Sealing Performance of Bolted Ball Joints by Gaskets: Numerical Simulation and Experiment

With the increasing utilization of bolted ball joint steel mesh structures in offshore floating platforms and deep-sea fish cages, the issue of seawater infiltrating the joints and members through the installation gaps of the bolted ball joint, leading to subsequent corrosion, has become increasingly prominent. This article presents an innovative method to improve the sealing performance of bolted ball joints. The approach involves creating sealed surfaces within the contact gaps between the sleeve and connecting components by adding circular grooves and sealing washers to both ends of the sleeve. Subsequently, a two-dimensional finite element analysis model of the bolted ball joint with the sealing structure was created using SOLIDWORKS 2021 and ANSYS Workbench 2022 R1. The study analyzes the sealing gasket’s contact pressure at various compression levels and evaluates its performance with bubble tests for air tightness. Research results show a linear relationship between the contact pressure and compression rate, achieving sealing pressures of 2.91 MPa, 4.22 MPa, and 5.95 MPa at compression levels of 8%, 11%, and 14%, respectively. Experimental testing demonstrates that the improved bolted ball joint exhibits excellent sealing performance.

Vanishing splendor: a comprehensive review of the decline in the original fish fauna of Lake Victoria

The presence of the non-native Nile perch (Lates niloticus) in Lake Victoria and the resulting ecological transformations have garnered significant attention from the scientific community. However, details regarding the timing, origin, and purpose of the fish introduction have remained elusive. This paper reviews fish fauna changes in Lake Victoria, investigates causes, and advocates for biodiversity conservation through diversity and sanctuary sites. It examines different historical periods to understand changes and guide effective conservation strategies. The introduction of Nile perch has led to a substantial decline and even extinction of many native fish species, particularly cichlids, resulting in ecological imbalances and economic challenges for local fishing communities. To address these pressing issues, ongoing conservation efforts are being implemented. These initiatives focus on promoting sustainable fishing practices, safeguarding critical habitats, and reintroducing native fish species. Furthermore, cage fish farming is being explored as a potential solution to alleviate pressure on wild populations, as suggested by various authors. Recommendations stemming from this study include conducting virtual population analysis for stock assessments of indigenous species, intensify conservation efforts, diversify fishing practices, expand cage fish farming, increase public awareness and education, and enhance policy and governance frameworks. By implementing these recommendations, there is optimism for the recovery and resilience of indigenous fish species in Lake Victoria, leading to the conservation of biodiversity and the promotion of sustainable livelihoods for local communities.