Submersible Cage Research Articles

Structural integrity of a submersible sea cage exposed to extreme oceanographic conditions

AbstractThis study focuses on the structural integrity analyses of a submersible cage with dimensions of 20 m in diameter and 10 m depth under extreme oceanographic conditions, including current speed of 0.5 and 1 m/s, combined with waves ranging from 2 to 5 m in height and a period of 7 s. Employing a dynamic simulation model based on finite elements, The study examines the stresses in the cage's pipes, as well as the tension in the bridle lines and mooring lines. Results indicate that submerging the cage leads to a reduction in peak tensions, with mooring lines experiencing a decrease of up to 32% and bridle lines experiencing a decrease of up to 59%. Furthermore, the stresses in the pipes exhibit a significant decline of up to 71.4%. These findings demonstrate that the submersible cage, when submerged, significantly reduces peak stresses, thereby decreasing the risk of structural loss or damage when the system is submerged.

Investment Feasibility Analysis of Large Submersible Cage Culture in Taiwan: A Case Study of Snubnose Pompano (Trachinotus anak) and Cobia (Rachycentron canadum)

Onshore farming for premium aquaculture is under scrutiny and criticism partially due to possible causes of adverse environmental impacts on other resource users and the surrounding environment. The best alternative to preventing or minimizing these impacts is to utilize open seawater by large submersible cage culture. The current operation in Taiwan has demonstrated that the culture operation is technically feasible but economically demanding because of high capital and operating costs. Therefore, this study conducted an economic analysis of the expansion of large submersible cage culture by selecting two premium species of snubnose pompano (Trachinotus anak) and cobia (Rachycentron canadum) and examined the profitability of large submersible cage culture investment. This study found that the current operation of four-unit cages highlighted a negative net present value and internal rate of return with a payback period of over ten and six years, respectively. Large submersible cage culture can be financially profitable when its operation unit expands from 8 to 24 units. Increasing unit cages to eight incurred a gross margin of 17.09%, BCR 1.21, with a payback period of 5.36 years. Expanding the operation to 24-unit cages was a potentially lucrative investment with a gross margin of 18.51%, BCR 1.23, PI 2.15, internal rate of return of 20.84%, and a payback period of 3.55 years. Sensitivity analyses revealed that market price and survival rate significantly impact the profitability of large submersible cage culture. Finally, it is suggested that producers could invest in 8-unit cages and maintaining the survival rate of snubnose pompano and cobia at 80% and 40%, respectively.

Effects of air replenishers on the growth and body morphology of four fish species in an underwater aquaculture system

The objective of this study was to investigate the effects of air replenishers on the growth, body composition, energy budget, and body morphology of four fish species through simulation within a fully submersible cage environment. The experimental species included Paralichthys olivaceous, which experiences swim bladder degeneration, and Lateolabrax japonicus, Oncorhynchus mykiss, and Cyprinus carpio, which are physoclistous, physostomous, and physostomous, respectively, with each species (N = 5) having an initial weight of 69.12 g, 73.10 g, 55.57 g, and 74.65 g, respectively. The four species were investigated in each trial designed with three different equipment for a 35-day period. The fish in the control group (Ctrl) were cultured in the tank with airstones, the mesh group (ME) used a mesh to keep the experimental fish from the water surface and airstones above the mesh, and the replenisher group (RM) had an air replenisher and airstones under the mesh. The results showed that there were no significant differences in the growth, body composition, energy budget, and body morphology of L. japonicus and P. olivaceus in different trials. For O. mykiss and C. carpio, compared to the Ctrl and RM groups, the specific growth ratio (reduced by 28.2% and 42.7%, respectively), protein content (reduced by 2.5% and 16.8%, respectively), and fat content (reduced by 14.2% and 27.2%, respectively) decreased. The proportion of feeding energy allocated to growth in the ME group also decreased, whereas that lost in respiration increased. An air replenisher can reduce the impact on the isolation of O. mykiss and C. carpio from the water's surface. Additionally, the streamlining of the body of O. mykiss in the ME group significantly decreased, whereas C. carpio in the ME group became more slender. This study implies that L. japonicus and P. olivaceus are not affected by isolation from the surface in a 1-month submergence culture, such as in a submersible cage, and the same effects on O. mykiss and C. carpio can be mitigated by air replenishment. Moreover, O. mykiss and C. carpio may adapt to negative buoyancy in submergence by changing body shape which generates more lift during swimming.

Effects of different types of air supplementation on rainbow trout confined underwater

Salmonid are farmed far offshore in a submersible cage in China, and air supplementation in the swim bladder is an important issue while the fish are confined in the submersed cage. The objective of this study is to test the effects of different types of air supplementation on the growth, energy budget, and fatty acid composition of the rainbow trout, Oncorhynchus mykiss, confined underwater. The fish were divided into four groups with four replicates (63.84 ± 2.03 g, 13 fish per tank): The control group fish (Ctrl) were cultured in a glass fiber tank with airstone; The mesh group (ME) used a net in a tank to keep the experimental fish from the water surface, and an airstone above the net; The airstone group (AM) added an airstone under the net; And the airdome group (DM) added an airdome under the net. At the end of a 35-day trial, the final mean weight (70.00 ± 1.63 g), percent weight gain (7.09 ± 0.96%) and survival rate (76.92 ± 0.00%) of the fish in ME group were significantly lower than those in Ctrl group (91.54 ± 5.19 g, 43.49 ± 10.35% and 100.00 ± 0.00%, respectively). The final mean weight of AM group was significantly lower than that of Ctrl group, whereas there were no significant differences in other growth indexes between control group, DM and AM group. The proportion of feeding energy allocated to growth in ME group was the lowest, the proportion in AM was significantly higher than ME group and lower than Ctrl group, and there was no significant difference between those in DM and Ctrl groups. The muscle saturated fatty acid level in Ctrl group was significantly lower than those in other groups. In conclusion, the growth of rainbow trout confined underwater for 35 days will slow down due to lower proportion of feeding energy allocated to growth and higher proportion to respiration. The addition of an airdome or airstone can partially compensate for the growth of the fish confined underwater long time. Rainbow trout confined underwater can partially compensate for the loss of buoyancy through increasing the muscle saturated fatty acid content.

Adjustment submersible cages for optimal fish farming: improved spatiotemporal Lotka–Volterra model for n species in partitioned area

The first goal of this research is to set improved spatiotemporal discrete Lotlka–Volterra model including n different species which occupy three dimensional area $$ \varOmega $$ and obey to any complex marine food chain. The area $$ \varOmega $$ is partitioned into R subregions, each subregion includes at least two species, and each species can occupy more than one subregion. The next concern is to increase production of special species which survive in a target subregion, taking into account the financial cost and the severe consequences on the environment. So, we propose two different approaches: optimal farming intra-subregion and optimal farming inter-subregions. One the one hand, we develop optimal program of farming intra-subregion in order to rise the growth rate of the concerned species. On the other hand, we aim to protect the concerned species by optimal adjustment of grids constituting the submersible cage in order to control the local interaction between the target subregion and its neighboring subregions. To the best of our knowledge, it’s the first time when permeability of submersible cages will be modeled and introduced in predator–prey models. To end, adequate numerical illustrations are implemented and discussed to prove the effectiveness of each approach.

상하가 원형 파이프로 구성된 부침식 가두리의 동적 거동 해석

In this research, the submersible fish cage was designed to avoid structural and biological damage during harsh sea conditions. The submersible cage system consists of netting, mooring ropes, a floating collar, floats, sinkers and anchors. Whole elements of the cage were modeled on the mass-spring model. The computer simulations were carried out to investigate the dynamic behavior of the cage and to calculate mooring line tension subjected to tidal currents and waves. As expected, the tension values in the mooring line of the submerged position are 36% less compared to that of the surface cage under the same loading conditions. As the wave was used in combination with the current velocity of 1m/s, the average tensile load for the submerged cage showed 85% of the value for the floating cage. The simulation results provide an improved understanding of the behaviors of the structure and valuable information on the optimized design of the cage system exposed to open ocean environmental factors.

Hydrodynamics of submersible aquaculture cage system using numerical model

A numerical model analysis was performed to analyze the motion and mooring tension response of submersible fish cage systems in irregular waves and currents. Two systems were examined: a submersible cage mooring with a single, high tension mooring and the same system, but with an additional three point mooring. Using a Morison equation type model, simulations of the systems were conducted with the cage at the surface and submerged. Irregular waves(JONSWAP spectrum) with and without a co-linear current with a magnitude of 0.5m/s were simulated into the model as input parameters. Surge, heave and pitch dynamic calculations were made, along with tension responses in the mooring lines. Results were analyzed in both the time and frequency domains and linear transfer functions were calculated.