Floating Fish Farms Research Articles

Analytical solution based on BEM to oblique waves scattering by thin arc-shaped permeable barrier applied for array of aquaculture cages

In this paper, linear oblique wave incident to a thin arc-shaped permeable barrier and an array of permeable circular cylinders was studied analytically. Two unique research objectives of this work include, considering the thickness for permeable material and the wavefield inside surrounded region by the permeable structure. The conventional boundary element method (BEM) is used to solve the governing equations of the problem. The mathematical relation between Bessel functions leads to representing the BEM-related integrals in the Fourier modes of Hankel function. This approach is useful as the singular integrals are accounted indirectly. Two basic geometries made by the permeable material are studied, including an arc-shaped and a circular geometry. The first geometry can represent a wave-breaking barrier in shallow water, while the latter can represent a floating fish farm in deep water. For the floating fish farm, the study is extended to the interaction between an array of cages. To quantify the amount of wave energy passed through the object, the Energy Transmission Index or ETI concept is introduced. ETI can be used as an indicator for permeable barriers performance.The results indicate that ETI is mostly a function of permeability rather than the wavenumber. In addition, the imaginary part of the permeability parameter plays an essential role in the problem of wave incident to permeable barrier, and it is necessary to be determined with enough accuracy. Furthermore, the shear force and bending moment on the base of the barrier and drift force and heeling moment on circular cylinders are studied. The results show, the drift force decreases as permeability and wavenumber increase. The results of this research are useful in the design of rigid circular offshore aquaculture fish cages and coastal barriers.

A Computational Fluid Dynamics Approach for Modeling the Fluid–Structure Interaction of Offshore Aquaculture Cages and Waves

Abstract Open ocean aquaculture cages became a promising alternative to traditional fish cage designs recently. The offshore environment implies larger loads on the structure and thus higher risk for fish loss. Floating rigid aquaculture cages with stiff nets are considered as a possible solution to cope with these new challenges. Their design process requires more advanced tools to account for the non-linear fluid–structure interaction. This paper presents a suitable numerical approach for analyzing the interaction of offshore aquaculture cages and waves using computational fluid dynamics. Here, a numerical wave tank accounts for the accurate propagation of the waves, and dynamic solutions are utilized for the cage system. Two-way coupling is enabled by accounting for the influence of the net on the fluid. The numerical model is validated against measurements for the loads on and the responses of a mobile floating fish farm in waves and current.

Effectiveness of Floating Breakwater in Special Configurations for Protecting Nearshore Infrastructures

This paper investigates the effectiveness of floating breakwaters consisting of two barges (L-shape), three barges (U-shape), four barges (barge frame), and conventional single floating breakwater. The floating breakwaters of different spatial layouts have sheltered internal gaps/moonpools when compared to their conventional counterparts. The motions of these floating breakwaters and their effectiveness in wave transmission and motion reduction of the protected floating bodies are evaluated. The study is conducted based on a subsystem of a floating hydrocarbon storage facility that combines a floating breakwater with two floating tanks, studied previously. Numerical models based on linear potential flow theory are built for these floating breakwaters with and without the floating tanks. The numerical models of the barge frame are validated through laboratory experiments, and the dipole damping lids to reduce the resonant fluid motions in the gaps/moonpools are calibrated with experimental results. The L-shape floating breakwater is found effective in reducing wave transmissions without the presence of the floating tanks, while the barge frame is the most effective in the motion reduction of the floating tanks. In addition, significant fluid resonant motions are identified for all investigated floating breakwaters, including the conventional one. Orienting the structure obliquely can improve the performance of the floating breakwaters of special configurations, especially the barge frame. The results and findings show the importance of considering the protected floating structures in the analysis when designing floating breakwaters for many types of marine structures, including floating fish farms and floating cities in coastal waters.

Antibiotics resistance in pathogenic bacteria isolated from water and sediment around the floating fish farms in the Nha Trang bay

To assess the impact of antibiotic use in aquaculture in Nha Trang bay, we conducted this study with the aim of assessing antibiotic resistance of opportunistic pathogenic bacteria isolated from water and sediment around shrimp/fish cages in the Nha Trang bay. 109 strains of Vibrio, Salmonella-Shigella and Aeromonas groups were isolated in the surrounding environment of farming areas in Dam Bay and Hon Mieu. Antimicrobial resistance test of these 109 strains showed that in the water environment in Dam Bay, TET (96.6%) and NIT (92.5%) were the two antibiotics with the highest rates of resistant bacteria while no bacteria were resistant to RIF. All 5 types of antibiotics had a statistically insignificant percentage of antibiotic-resistant bacteria in water samples at Hon Mieu, ranging from 33.3% to 68.9%. Also in the water environment, the rate of antibiotic-resistant bacteria in Dam Bay was not influenced by the distance to the cages (42.5–66.6%). Meanwhile, in Hon Mieu, the highest rate of resistant bacteria was observed at the distance of 200 m (100%) away from cages and the lowest rate at the distance of 100 m (20%). In the sediment environment around the cages, both the Dam Bay and Hon Mieu farming areas showed the highest rates of antibiotic-resistant bacteria against TET, NIF and RIF had the lowest rate of resistant bacteria. Among the total of 109 strains tested for antibiotic resistance, 2 strains labeled TCBS_HM200 m and SS_HM200 m were found to be resistant to all 5 tested antibiotics. These two strains were respectively identified as Vibrio harveyi and Oceanimonas sp.

Wave and Current Effects on Floating Fish Farms

The paper is partly a review on hydrodynamic and structural aspects offish farms. In addition, new numerical results are presented on the stochasticbehavior of bending stresses in the floater of a realistic net cage in extreme waveconditions. The behavior of traditional-type fish farms with net cages and closedfish farms in waves and currents is discussed. Hydroelasticity can play asignificant role for net cages and closed membrane-type fish farms. The many meshesin a net cage make CFD and complete structural modeling impracticable. As anexample, a hydrodynamic screen model and structural truss elements are instead usedto represent the hydrodynamic loading and the structural deformation of the net. Inaddition, the wake inside the net due to current plays an important role. Thedescribed simplified numerical method has been validated by comparing with modeltests of mooring loads on a single net cage with two circular elastic floaters andbottom weight ring in waves and currents. It is discussed which parts of thecomplete system play the most important roles in accurately determining the mooringloads. Many realizations of a sea state are needed to obtain reliable estimates ofextreme values in a stochastic sea. In reality, many net cages operate in closevicinity, which raises questions about spatial variations of the current and waveenvironment as well as hydrodynamic interaction between the net cages. Live fishtouching the netting can have a non-negligible influence on the mooring loads. It isdemonstrated by numerical calculations in waves and currents that a well boat at anet cage can have a significant influence on the mooring loads and the bendingstresses in the floater. The latter results provide a rational way to obtainoperational limits for a well boat at a fish farm. Sloshing has to be accounted forin describing the behavior of a closed fish farm when important wave frequencies arein the vicinity of natural sloshing frequencies. The structural flexibility has tobe considered in determining the natural sloshing frequencies for a membrane-typeclosed fish farm. Free-surface non-linearities can matter for sloshing and can, forinstance, result in swirling in a certain frequency domain for a closed cage with avertical symmetry axis.

Mytella strigata (Bivalvia: Mytilidae): an alien mussel recently introduced to Singapore and spreading rapidly

ABSTRACTThe American brackish-water mussel Mytella strigata is reported from Singapore for the first time. In 2016 a survey of intertidal hard structures in the Johor Straits revealed its almost ubiquitous presence in high mean densities, up to 124 ± 32 individuals 25 cm−2 along the shoreline. Subtidal nets employed by floating fish farms were also fouled with this species. Densities exceeding 10,000 individuals 100 cm−2 were observed, to the exclusion of its relative Perna viridis, the Asian green mussel. Size-frequency analyses of shells indicated the presence of both juveniles and adults. Juveniles have an extremely variable shell surface pigmentation. The adults, reaching 5 cm in shell length, generally have a thick dark greenish brown to almost black periostracum, but bright green and olive green individuals, some with distinctive brown streaks, have also been observed. However, sequences of the mitochondrial COI gene were consistent with mussels from Brazil, Colombia and Ecuador, where they are natively distributed, while shells were reconcilable with type material. The species may have been transported in ballast water and/or with fouling directly from its native provinces, or spread from the Philippines where there are already established populations of M. strigata, possibly since the nineteenth century.

Wave-Induced Accelerations of a Fish-Farm Elastic Floater: Experimental and Numerical Studies

Numerical simulations and experiments of an elastic circular collar of a floating fish farm are reported. The floater model without netting structure is moored with nearly horizontal moorings and tested in regular deep-water waves of different steepnesses and periods without current. Local overtopping of waves was observed in steep waves. The focus here is on the vertical accelerations along the floater in the different conditions. The experiments show that higher-order harmonics of the accelerations matter. A three-dimensional (3D) weak-scatter model with partly nonlinear effects as well as a 3D linear frequency-domain method based on potential flow are used. From their comparison against the measurements, strong 3D and frequency dependency effects as well as flexible floater motions matter. The weak-scatter model can only partly explain the nonlinearities present in the measured accelerations.

Role of fish farm fouling in recolonisation of nearby soft-bottom habitats affected by coastal aquaculture

Organic loading from fish farming constitutes a significant disturbance to marine sediment, normally reducing species abundance and richness and creating disturbed patches in soft-bottom communities. In contrast, floating fish farms harbour a high abundance of invertebrates associated with fouling communities, particularly amphipods. Changes in macrofaunal recolonisation induced by fish farms were researched using amphipod assemblages as a useful representative group. The objectives of this experiment were: (1) to test the effect of fish farms on amphipod colonisation processes in defaunated sediments and (2) to define the influence of surrounding natural and artificial habitats as sources of initial colonisers. Experimental design included 36 plastic trays placed on the sea bottom (25–28m depth) in fish-farming and control areas and retrieved one month after placement date. Significant differences were found in amphipod assemblage composition in control versus farm sites. While the recolonisation process in control areas depended on the species present in the sediments adjacent to the experimental trays, in fish-farming areas the recolonisation was strongly dependent on the input of amphipods from fouling communities. It is the first time that a spillover effect from fouling communities on floating habitats into the benthos is detected in the coastal areas. If the organic enrichment of aquaculture sediments is moderate, the ecological services of benthic habitats may be balanced, at least partly, by biomass exported from fouling communities on the same fish farms.

Tracked mangrove horseshoe crab Carcinoscorpius rotundicauda remain resident in a tropical estuary

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 17:235-245 (2012) - DOI: https://doi.org/10.3354/ab00477 Tracked mangrove horseshoe crab Carcinoscorpius rotundicauda remain resident in a tropical estuary Lesley Cartwright-Taylor*, Harn Hua Ng, Ter Yang Goh Nature Society (Singapore) (NSS), 510 Geylang Road, #02-05 The Sunflower, Singapore 389466 *Email: cartwrighttaylor@gmail.com ABSTRACT: Mangrove horseshoe crab Carcinoscorpius rotundicauda were tracked for 6 mo in the tropics using acoustic telemetry to determine whether they either show homing behaviour, remain near the site of capture, or travel to the open sea. Twelve adult horseshoe crabs were caught on the Mandai mudflats at Kranji and acoustic telemetry transmitters attached. Six acoustic receivers were deployed suspended from floating fish farm platforms ~1 km apart along the Strait of Johor, an estuary off the north coast of Singapore. Four individuals, 2 of each sex, were used in each of 3 tests: 4 crabs were released at the site of capture, 4 were released at a second site ~5.7 km away to determine if they exhibited homing, and 4 were caught along the muddy beach at the second site, tagged and released into deep water under one of the receivers. Although there were gaps in detection, 11 of 12 crabs were located intermittently within ~6 km of the point of release. One crab disappeared after 5 d. Homing was not exhibited, and the crabs were detected within the estuary for 6 mo. We concluded that the crabs in the tropical estuary, where there are no seasons or marked changes in water temperature, showed no tendency to travel out to sea and did not exhibit homing behaviour or any synchronized movement pattern to deeper waters. KEY WORDS: Mangrove horseshoe crab · Telemetry · Homing · Movement · Tropics Full text in pdf format PreviousNextCite this article as: Cartwright-Taylor L, Ng HH, Goh TY (2012) Tracked mangrove horseshoe crab Carcinoscorpius rotundicauda remain resident in a tropical estuary. Aquat Biol 17:235-245. https://doi.org/10.3354/ab00477 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 17, No. 3. Online publication date: December 13, 2012 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2012 Inter-Research.

Dynamic analyses of floating fish cage collars in waves

An extended 3D hydroelasticity theory is used in the frequency domain to predict the dynamic response of 5 by 2 floating fish farm collars in regular waves. Hinge modes in two directions and flexible torsional modes are all considered in the analyses. The dry and wet resonant natural frequencies for each rigid relative motion and the flexible modes are also calculated. The results show that the modes, flexible bending and torsional modes, as well as their interactions, greatly contribute to the dynamic response of the floating collar system. From a design point of view, the effects of the connector rotational stiffness on the dynamic response of the structures are also analysed.

Assessment of Fatigue Damage of Floating Fish Cages Due to Wave Induced Response

Floating fish cages provide the main production utilities for salmon farming. However, despite their pivotal role in production safety as well as in protection of the environment, there is still much room for improvement in relation to verified structural design procedures and computerized tools for structural analysis. To a large extent, they can be regarded as not being in accordance with the state-of-the-art of structural analysis and design for more traditional types of marine structures. In this paper, a study of fatigue design for floating fish farms is presented. This study is based on a structure that is being applied by the Norwegian fish farming industry today. The floater is made of steel cylinders that are configured as a square. The formulation for the wave loading is based on a combination of potential theory and horizontal drag forces on the floater. Horizontal and vertical drag forces on the netpen are also accounted for. A fatigue design procedure for floating fish farms in steel is suggested. The procedure is based on a time domain analysis of the structure in irregular waves. For each seastate, 1/2 h (real time) analysis is performed and the stress history for an assumed critical location is computed. Based on the stress histories, the fatigue damage is estimated by application of rain flow counting and a given SN curve. The scatter diagram for the seastates at a given location is generated from the associated wind speed distribution.

Numerical and experimental study of submerged supple nets: Applications to fish farms

Our aim is to investigate the behavior of submerged supple nets. This work generates many problems owing to the discontinuous and highly flexible nature of the nets. Only the action of external forces can bring an infinitely flexible structure like a net into a definite shape. When considering supple nets immersed in a fluid, these external forces themselves depend on the net geometry. A numerical method to solve this fluid-structure coupling problem is proposed, and is applied to fish farms. In order to validate the calculation model of the hydrodynamic forces on the mesh sides, we measured the hydrodynamic forces on a plane panel of netting spread across a transverse current. We thus proved that the Landweber model modified according to the Richtmeyer formula as regards friction gives good results. The calculated shape of the fixed net cage is qualitatively in accordance with flume tank observations. We have adapted the algorithm to the study of the dynamic behavior of floating fish farms.

Effects of a floating fish farm in Kiel Fjord on the sediment

The effects of a floating fish farm in Kiel Fjord, Western Baltic, have been studied in the summer 1991 by underwater video, sediment and benthos samples. Significant alterations of the benthos and sediment geochemistry as compared to control stations were documented. The sediment under the farm is anoxic, organically enriched (1.5 to 3.5 fold), covered by sulfur bacteria, and almost free of benthic macro fauna. Rates of decay of organic carbon and oxygen uptake (derived from porewater profiles) are high and account for 100–150 mmol m-2 d-1 in summer.

Current forces on, and water flow through and around, floating fish farms

The wake generated by a screen or a net is analysed by the linear free-wake equations in conjunction with an eddy viscosity formulation. The behaviour of the near and far-field wake is investigated, and a relationship between the drag coefficient and the wake velocity is derived. A method for calculating the current forces experienced by the net structure and the resulting deformation is derived and compared with model tests. The effects of the wake behaviour and the deformation of the net cages, on the design and operation of floating fish farms are discussed and some recommendations are given.

Historical development of salmon culture

By 1989, the production of farmed Atlantic salmon in Norway had increased to 118 000 t which was close to 70% of the world's total production that year. This production is marketed through the Norwegian Fish Farmers' Sales Organization (FOS) which has the sole right of first-hand sale of all farmed fish and shellfish.By restricting the numbers and maximum size of fish farms by licensing, the Ministry of Fisheries tries to promote the development of a profitable, viable and economically independent regional industry and to develop it as one of the main forms of industry for the coastal population.The diseases furunculosis and “Infectious Anaemia of Salmon” (IAS) have, during the last 2 years grown to be the major threats to the salmon industry. The danger of infecting wild populations and other fish farms has led the veterinary authorities to impose restrictions like quarantine, sanitary slaughtering or total killing and destruction on infected fish farms.Much attention has also been paid to the increased use of medicines and chemicals, and releases of nutritients to the environment. A strict control system has been established to prevent fish with antibiotic residues from being marketed.To reduce the effects of fish farm escapees on the natural stocks, protective measures, like areas free of fish farms around the most important salmon rivers have been established. Recently, the Fish Farm Escapee Committee was formed to propose measures to reduce the number of escapees. One of the proposed measures is a type-approval of all floating fish farm installations.The group of the aquaculture industry has also led to a tremendous increase in the efforts pest on aquacultural research. Within the field of product development, and in private and public research and development work, a systematic effort is being made to make the Norwegian fish farming industry more efficient.

Dynamic Response of a Floating Fish Farm to the Ocean Waves

The problem of the dynamic behaviour of a floating fish habitat by ocean waves is investigated theoretically in this paper. A mathematical model for determing the dynamic displacement of a aquaculture are derived by using a empirical relationship of wave force acting on the plain net. The culclations resits arecompared with the wave tank tests under various wave conditions and they show good agreement. Also, a new field measurement system of the movement of fish farm structure is developed and results of laboratory tests of the system are presented.

Mass mortality in Siganus canaliculatus due to streptococcal infection

Mass mortality of cultured Siganus canaliculatus occurred in floating fish farms located off the north-east coast of Singapore. Some fish showed symptoms such as change in body coloration, sluggish movement and blindness. Prior to death, all fish showed violent movement, convulsion and seizure. Smears of blood and brain showed the presence of bacteria suggesting acute septicemia. The hematocrit was 12% lower than normal. A thick whitish layer (6.8%) containing numerous bacteria appeared above the column of packed red cells. The bacteria isolated from the diseased fish were found to be α-hemolytic grampositive cocci in chains. The species has characteristics similar to Streptococcus faecalis and Streptococcus faecium. Other species of fish cultured in the farm at the same time (e.g., grouper, Epinephelus tauvina, and sea bass, Lates calcarifer) did not succumb to the diseage.