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1.
Abstract. The concept of farming Atlantic salmon, Salmo salar L., beyond smolt stage in sea water started in Norway and Scotland in 1967–1968, using natural enclosures or sea water ponds. Cage culture has since 1969 developed to be the dominating method. Atlantic salmon is cultivated in more than nine countries with a production of 235400t in 1990. Incubation of eggs, hatching, first feeding and smolt production have to a large degree been standardized. Various types of incubator systems and holding units are briefly presented and discussed. There has recently been a trend to move ongrowing cage farms from inshore and sheltered waters to more open and offshore locations. The various types of cages and supplemental equipment for the two options are compared and evaluated. The offshore trend is a more expensive and difficult technology than existing inshore farming methods. Sea enclosures and net enclosures are less attractive. There is new interest in pump ashore systems. Large land-based farms have been built in six countries with varying success. The amounts of water required are enormous and constructions costs are high, but running costs are comparable to cage culture. Great improvements have taken place for both smolt farms and pump ashore farms in treatment of water, use of heat exchangers, filtration of water, disinfection, aeration, oxygenation, photoperiod and light control, automatic feeding, internal transport, handling of fish and surveillance and control systems for fish and water. The problems and prospects of farming are discussed in relation to new and old technology.  相似文献   

2.
HDPE双管圆形深海抗风浪网箱的研制   总被引：7，自引：0，他引：7  
通过网箱结构的对比分析、材料选择和网箱模型试验,并针对进口网箱在我国海区使用中存在的问题,采用自主开发的HDPE网箱框架专用管材和六边形网目尼龙网衣,在网箱结构设计和制作技术上进行了多项创新性改进,自行研制了HDPE双管圆形结构的抗风浪网箱。波浪水槽模型试验表明,网箱抗浪能力可达7m波高以上,在原型流速102．9cm／s时,网箱容积损失率约为19．8％。研制的周长50m,水体2000m^3的试验网箱,经两年海区养殖验证,经历8～9级大风38次,10级以上大风3次,最大流速72cm／s,网箱系统和养殖鱼类安全。  相似文献   

3.
In response to the increased demand for food in general and food fish in particular, offshore mariculture is faced with the technological challenge of providing a viable cage design concept that is able to function effectively in high-energy environments. The single-point-mooring (SPM) fish cage systems for offshore fish farming are gaining support due to their environmentally friendly and economically favorable characteristics. An SPM self-submersible cage design concept has been identified as a potential mariculture cage concept for offshore waters, and the success of this concept depends on the operational performance in the offshore environment. Therefore, the current paper investigates the submergence characteristics of such a cage system in regular waves with a following current. This work also investigates the possibility of manipulating the cage system to achieve the desired submergence under different environmental conditions. The analysis demonstrates good potential for the self-submersible SPM cage concept in the simulated load cases because the response of the cage system to increasing wave height implies considerable additional submergence for realistic environmental conditions in offshore sites. The results also suggest that the concept allows adequate flexibility for use of the cage system in a range of environmental conditions.  相似文献   

4.
Naupliar copepods were distributed at similar concentrations over the waters inshore and offshore of the Kuroshio Current off central Japan in early spring 1993 and 1994, overlapping with the distribution of early feeding larvae of Sardinops melanostictus . Although N, P, Si and chlorophyll a concentrations were higher in the waters inshore of the Kuroshio axis than in the offshore waters, the mean concentrations of nauplii were not statistically different between the two waters. Food availability for larval S. melanostictus did not seem to be different between the two waters in terms of the mean food concentrations. Using the critical food concentration (>9 nauplii L–1) for 25% survival during 3 days after first feeding derived from a rearing experiment, percentages in number of stations or water samples with nauplii concentrations >9 nauplii L–1 were higher in the inshore waters than in the offshore waters in both years examined. Considering that fish larvae may depend on small-scale patchiness of food for their survival, the inshore waters seemed to be more favourable for first-feeding larvae than the offshore waters.  相似文献   

5.
Novel design and analysis procedures are needed for engineering of the offshore fish farms utilizing copper alloy netting. Existing technologies developed for fish cages with polymer nets are not directly transferrable to the fish cages with copper netting. In particular, the structural integrity of fish cage/mooring systems, and initial high costs of fish cages with copper netting are two major concerns in the engineering for open ocean aquaculture. We propose the modified engineering procedures, which address these concerns and allow for retrofitting of existing fish farming systems with polymer nets. These procedures are illustrated by considering two case studies: design of a rigid-frame and flexible gravity-type fish cages. Performance of both designs is analyzed after the field trials in the North Atlantic and South Pacific oceans, correspondingly.  相似文献   

6.
The effects of four levels of diffused aeration (0, 6, 12, and 24 hours/day) and two stocking densities (400 and 600 fish/m3) on the culture performance of caged Florida red tilapia were evaluated in 1 m3 cages in a 2 ha watershed pond on St. Croix, U.S. Virgin Islands. Fish obtained a nutritionally-complete (36% protein), floating feed from demand feeders for 143 to 146 days. Diffused aeration had no significant ( P > 0.05) effect on fish growth, survival, feed conversion, and production in cages. Combined across all levels of diffused aeration, fish stocked at 400/cage had a greater growth rate (2.21 vs. 1.97 g/day), larger final body weight (370 vs. 335 g), and a lower feed conversion ratio (1.69 vs. 1.80) than fish stocked at 600/cage ( P < 0.05). The final biomass of fish stocked at the higher density (181 kg/m3) was greater than at the lower density (140 kg/m3). The enhancement of water exchange rates by diffused aeration did not increase tilapia growth rate or production in cages.  相似文献   

7.
在水库进行了网箱养殖团头鲂试验，采取网箱配套养殖鱼种和成鱼，自己设计饵料配方、合理投喂和防治鱼措施，１５只网箱总面积３７５ｍ＾２，共产商品鱼２３５０５ｋｇ，平无尾重４５１ｇ，盈利６．６３５万元，折合亩净产３５６１６ｋｇ，亩盈利１１．８万元。  相似文献   

8.
Aquaculture is the fastest growing food producing sector in the world. Considerable interest exists in developing open ocean aquaculture in response to a shortage of suitable, sheltered inshore locations and possible husbandry advantages of oceanic sites such as increased water quality and oxygen supply, which improve production efficiency and the quality of fish. The extreme weather conditions experienced offshore leads to a focus on new structure concepts, remote monitoring and a higher degree of automation in order to keep the cost of constructions with an economically viable range. This paper proposes tensegrity structures in the design of wave compliant structures for offshore aquaculture. The objective of this paper is to study several different combinations of pre-stress and stiffness and determine how they influence the stiffness of the tensegrity structure. The finite element analysis program ABAQUS™ has been used to investigate the load carrying capacity of a tensegrity beam structure. The stiffness properties of the tensegrity beam were observed to be highly non-linear and dependent on pre-stress and spring stiffness. When designing a tensegrity beam, both pre-stress and spring stiffness should be considered to ensure the desired structural properties. A large strength to mass ratio and promising properties with respect to control of geometry, stiffness and vibration could make tensegrity an enabling technology for future developments. The suggested concept, the tensegrity beam, shows promising stiffness properties in tension, compression and bending, which are relevant for development of open ocean aquaculture construction for high energy environments.  相似文献   

9.
Within a few months of the establishment of a sea cage salmon farm in the Marlborough Sounds, New Zealand, sediment physical and chemical characteristics reflected the extremely high sedimentation rate immediately underneath the fish cages. In the surface sediment, dry weight was reduced to about one-third, density was halved and the volatile solids content increased about seven-fold compared with nearby sediments. Similarly, the sediment pools of ammonium, organic N and total phosphorus were much higher underneath the cages than at farther removed sites. The total N/P ratios were the same (1.5) in the surface sediment underneath the cages and in the feed but markedly higher in the less affected areas. In situ nitrification and denitrification were not measurable in the immediate vicinity of the salmon farm. The potentials for nitrification and denitrification gradually increased from virtually nil underneath the fish cages to commonly observed rates about 30 m from the cages. The complete absence of denitrifying enzymes in the salmon farm sediment to a depth of 6 cm explained why nitrate diffusing from the water column into the sediment was not denitrified. Within 10 m of the fish cages the bulk of added 15N-nitrate was reduced to 15N-ammonium. The results demonstrate that nitrification/denitrification in the immediate vicinity of a sea cage fish farm is not a significant mechanism of N removal.  相似文献   

10.
Mortality has received insufficient attention as a fish welfare topic. Here, we aim to prompt fish farming stakeholders to discuss fish mortalities in relation to welfare. Mortality in farmed fish populations is due to a variety of biotic and abiotic causes, although it is often difficult to differentiate between underlying and immediate causes of mortality. Most mortality appears to occur during episodes associated with disease outbreaks and critical periods (in development or production). Most causes of mortality can be assumed to be associated with suffering prior to death. As mortality rates in farmed fish populations are suspected to rank amongst the highest in commonly farmed vertebrate species, mortality should be a principal fish welfare issue. Long-term mortality rates can be used as a retrospective welfare performance indicator and short-term mortality rates as an operational welfare indicator. Scrutiny of mortality records and determining causes of death will enable action to be taken to avoid further preventable mortality. The welfare performance of fish farms should only be judged on levels of predictable and preventable mortality. Fish farmers will already be monitoring mortality due to commercial and legal requirements. As profitability in fish farming is directly linked to survival, confronting mortality should ultimately benefit both fish and farmers.  相似文献   

11.
Intensification of farm technologies has shown high potential in improving farm production and enhancing rural food and income security. Intensification, however, is commodity-specific with high-value crops intensively produced. Farmed fish is one of the high-value crops introduced in the study area to meet the above ends. The problem, however, is that the level of intensifying fish farming technology has been very low leading to discouraging results. A study was conducted in Morogoro and Dar es Salaam Regions, Tanzania, to identify socio-economic factors that influence the intensification of fish farming technology. Data were collected from 234 respondents randomly sampled from 25 selected villages and were analyzed using multinomial logistic regression model. Results indicated that age, extension education, profitability, marketability, risk, palatability and easiness to obtain farmed fish were significant in explaining the intensification of fish farming technology. Three recommendations emerge from this finding. First, there is need to provide extension education to the practicing farmers on various aspects of fish farming. The probability of intensifying fish farming is higher for knowledgeable farmers. Second, technology developers should strive to reduce the risk of farming fish and improve the profitability and marketability of farmed fish. Finally, any analysis focusing on intensification of a fish farming technology should not confine itself to agronomic and socio-economic characteristics but should also encompass food characteristics of the technology. Food variables such as palatability and easiness to obtain farmed fish have been shown to influence the intensification of fish farming technology.  相似文献   

12.
ABSTRACT:   Sea water environmental conditions over annual cycles were investigated and compared between two oyster farming areas, western Hiroshima Bay and Oginohama Bay (a branch of Ishinomaki Bay) in Miyagi Prefecture, to appropriately manage oyster culture or more efficiently utilize farming areas. The environmental parameters of temperature, salinity, nutrient concentrations (NO2–N, NO3–N, NH4–N, PO4–P, and SiO2–Si) and size-fractionated chlorophyll- a (<0.2, 2–20, >20µm), and abundances of microzooplankton were measured in each bay at the surface, and 2 and 5 m depth layers. Differences in the annual mean values and results with monthly paired Student's t -tests showed that salinity was lower, and temperature, nutrient (especially PO4–P) and chlorophyll- a concentrations, and abundance of microzooplankton, were higher in Hiroshima Bay than in Oginohama Bay. Differences in environmental conditions between inshore and offshore areas of each bay suggest that inflows of river water in western Hiroshima Bay and sea water from offshore had the most significant effects on the environmental conditions. It is concluded that such oceanographic and biological differences strongly affect the oyster farming system, especially regarding the optimum usage of offshore areas in Summer under clean, cold and stable seawater conditions, rather than food quantity in Hiroshima Bay, and under more abundant food conditions in Oginohama Bay.  相似文献   

13.
Abstract  The prevalence of escaped farmed Atlantic salmon, Salmo salar L., in the River Ewe, western Scotland, was assessed. After the establishment of smolt cages in the catchment and marine cages near the river mouth during 1986–1987, approximately 425 000 parr and smolts, and 122 000 growers have escaped. Between 1987 and 2001, farmed salmon occurred in the rod fishery in 13 of the 15 years, contributing at least 5.8% of the total catch, with a maximum annual frequency of 27.1%. It was estimated that <1% of fish escaping from the marine cages entered the river, but contributed at least 27% of potential anadromous spawners in 1997. Radiotagged, farmed fish in 2001 probably spawned in three subcatchments also used by tagged wild fish. Despite the likelihood of hybridisation there was no change in the median weight or marine age of wild fish, but smolt age decreased significantly ( P  < 0.02). The Ewe has a depleted wild salmon population (≤900 anadromous adults), and further genetic introgression by escapees should be prevented.  相似文献   

14.
The escape of small smolt through farm cage netting is a major challenge faced by the Norwegian salmon farming industry. Escape can occur when the smolt placed in the cages are smaller than the size estimated by the farmers. Furthermore, one may assume wrong mesh-properties as the cage netting change shape and/or state from stiff (mesh bars with tension) to slack (mesh bars without tension) due to sea currents or waves and become more suitable for penetration. The latter represents an increased risk for cages placed in more exposed sea areas, which is a growing trend in the industry due to increased demand for farming sites. The potential influence of mesh shape and state on the risk of escape from salmon farm cages is predicted. The morphological characteristics of salmon smolt are assessed and used to determine the risk of potential escape through meshes of different sizes, shapes and states. The results showed that fish smaller than 47 g and 201 g have the potential to escape through 30 mm and 50 mm meshes, respectively. In general, the risk of smolt escape is highest when the meshes in the netting are slack. Semi-slack meshes with mesh openness of between 65 and 95 % also present a higher risk of smolt escape than square stiff meshes. The highest risk of escape was identified at approximately 80 % mesh openness. This study illustrates the importance of mesh states in fish farming cage nettings. In many cases the minimum smolt size needed to maintain an escape risk below 1 % was approximately twice as large for slack square meshes than for stiff square meshes of the same size.  相似文献   

15.
The influence of cage aquaculture on the attraction and aggregation of wild fish was evaluated with an experimental tilapia farming structure. The structure was installed in the Corvo River, Rosana Reservoir, Paranapanema River basin, for 140 days. Samples were taken before and after farming began. Gillnets on the surface and near the bottom at different distances from the cages (0, 100 and 400 m) were used for fish sampling. The effects of the food supply at two protein levels were also analysed: Phase 1 = 32% PB and Phase 2 = 28% PB. Changes in species richness and abundance were observed, with the number of individuals and the fish biomass increasing significantly just after the farming began. Some species, such as Iheringichthys labrosus, presented increased abundance near the cages, while others, such as Plagioscion squamosissimus, were more abundant far from the cages. Auchenipterus osteomystax was the most abundant species during the experiment, especially when the protein content of the pellets was higher. It was demonstrated that farming tilapia in cages profoundly altered the abundance and composition of the wild ichthyofauna, suggesting the need to propose effective regulations for such activities, including fisheries restrictions in farmed areas or even the prohibition of cage farming.  相似文献   

16.
Trash fish/low valued fish is still the most commonly used feed in marine cage culture in Asia. Use of trash fish is controversial with regard to the sustainability of the farming practices, and related issues on environmental degradation. In this study, the results of farm based trials on Asian seabass (Lates calcarifer) and tiger grouper (Epinephelus fuscoguttatus) to evaluate the efficacies of the use of commercial pellet feed in comparison to trash fish/low valued fish in marine cages in Thailand are presented. In spite of the variations observed in each of the farm sites, the results indicate that the overall growth performances and fish survival rates between the two feed types were similar, for both species. However, better cost‐benefit and resource use were recorded for fish reared on trash fish/low valued fish. No significant differences were observed in water quality parameters, dissolved oxygen, transparency and ammonia, between sites where pellet or trash fish were used, inside and outside the cages and for both species. The results of the present study are discussed in the light of the current controversies on the use of trash fish/low valued fish in marine cage culture.  相似文献   

17.
Two field studies were carried out with farmed Atlantic salmon (Salmo salarL.) in sea cages to examine various effects of artificial light (AL) and the vertical distribution of salmon on lice infestation.

The use of AL light caused an overall increase in lice infestation in both experiments. The first study showed that salmon held at 0–4 m depth in cages developed higher infestation than salmon held at greater depths (4–8 and 8–12 m) under both natural light (NL) and AL. In the second study, salmon maintained in 14-m deep sea cages that were exposed to AL with different light intensities. The AL treatments resulted directly in different diel and seasonal patterns of vertical distribution of the salmon and also different temporal patterns in lice infestations. So indirectly the infestation pattern appeared to be correlated with median day-time swimming depth of the salmon.  相似文献   


18.
This study evaluated the ambient noise effect of onshore and offshore aquaculture systems on oxidative status and on some immune parameters in gilthead sea bream (Sparus aurata) juveniles. The experiment was performed for 40 days, projecting two different playlists of acoustic stimuli: offshore aquaculture noise condition that created the typical acoustic field in proximity of an offshore sea cage for fish farming, using a random sequence of quite sea background and boat noises; and onshore aquaculture noise condition that represented the acoustic field inside an open concrete tank for fish farming. A third group without any acoustic projection was used as a control. After 40 days from the beginning of acoustic noise, fish exposed to the offshore aquaculture condition showed significantly higher levels of total oxidant status, lysozyme activity, antiprotease activity and white blood cells together with a lower albumin/globulin ratio in comparison to fish from the control group; whereas fish exposed to the onshore condition showed analytical data placed between the other groups, though never significantly different. These results demonstrate that the offshore aquaculture noise, and in particular the sea soundscape, adversely influences the oxidative status and the immune function of gilthead sea bream determining a mild stress condition that could affect the sea bream welfare.  相似文献   

19.
哑铃湾网箱养殖海区表层沉积物磷的含量特征   总被引：5，自引：0，他引：5  
在哑铃湾不同养殖历史网箱下、距离网箱50m和100m以及对照海区共布设8个采样点,于2002年4月~2003年1月分四季采集表层沉积物样品,对沉积物中总磷、无机磷和有机磷进行了测定,分析了调查区磷的空间分布和季节变化特征。结果表明:哑铃湾海水养殖网箱下沉积物磷含量明显高于对照点,沉积物中总磷是对照点的3.71~9.99倍。养殖历史越长,沉积物中的磷含量越高;网箱养殖引起的沉积物磷累积仅限于网箱下及距离网箱50m范围内,对距离100m以外的海区影响较小;沉积物中的无机磷占70%以上,以无机磷为主;养殖历史较长的东升村养殖区沉积物磷的季节变化明显,有机磷的变化与养殖活动密切相关。  相似文献   

20.
A two‐factor experiment was performed to evaluate the effects of cage colour (black or white 0.5 m3 experiment cages) and light environment (natural sunlight or reduced level of natural sunlight) on the skin colour of darkened Australian snapper. Each treatment was replicated four times and each replicate cage was stocked with five snapper (mean weight=351 g). Snapper exposed to natural sunlight were held in experimental cages located in outdoor tanks. An approximately 70% reduction in natural sunlight (measured as PAR) was established by holding snapper in experimental cages that were housed inside a ‘shade‐house’ enclosure. The skin colour of anaesthetized fish was measured at stocking and after a 2‐, 7‐ and 14‐day exposure using a digital chroma‐meter (Minolta CR‐10) that quantified skin colour according to the L*a*b* colour space. At the conclusion of the experiment, fish were killed in salt water ice slurry and post‐mortem skin colour was quantified after 0.75, 6 and 22 h respectively. In addition to these trials, an ad hoc market appraisal of chilled snapper (mean weight=409 g) that had been held in either white or in black cages was conducted at two local fish markets. Irrespective of the sampling time, skin lightness (L*) was significantly affected by cage colour (P<0.05), with fish in white cages having much higher L* values (L*≈64) than fish held in black cages (L*≈49). However, the value of L* was not significantly affected by the light environment or the interaction between cage colour and the light environment. In general, the L* values of anaesthetized snapper were sustained post mortem, but there were linear reductions in the a* (red) and b* (yellow) skin colour values of chilled snapper over time. According to the commercial buyers interviewed, chilled snapper that had been reared for a short period of time in white cages could demand a premium of 10–50% above the prices paid for similar‐sized snapper reared in black cages. Our results demonstrate that short‐term use of white cages can reduce the dark skin colour of farmed snapper, potentially improving the profitability of snapper farming.  相似文献   

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