Sager: Just because nobody sends you the info straight to your mailing address doesn't mean it doesn't exist. Here's something to start because you seem a little lazy to do your own homework:
THE SILFURSTJARNAN FISH FARM
The Silfurstjarnan fish farm is a land-based system where fish are reared in a number of individual tanks of various sizes. Construction began during the autumn of 1988. Building of the fish tanks was more or less completed a year later. A small hatchery for arctic char was built elsewhere in Öxarfjördur in the same year. At the hatchery, artesian cold and hot waters from springs or drill holes are used. The temperature can be adjusted to increase or reduce the fish growth, which is important in order to secure delivery of the same size fish product throughout the year. Early on, the company hired an additional hatchery for salmon in S-Iceland with similar conditions. Now, the salmon smolt is bought from Stofnfiskur Ltd., where a breeding research programme based on Norwegian stocks has produced the best salmon stock in Iceland for fish farming. The main fish farm now consists of the following utilities (Figure 3):
Freshwater supply Seawater supply
Warm water supply Aeration system
Oxygenation system Tank rearing system
Effluent/filtering system Feeding system
Monitoring/control and Electrical supply and emergency
alarm system back-up system
Fish handling and Fish processing and packing plant
grading system
Water is pumped from the boreholes by downhole submersed pumps of 80 - 300 l/s capacity. Seawater is pumped by standard horizontal centrifugal pumps of 125 l/s each. Pumping head is variable, generally in the range of 20 -30 m. Presently, about 700 l/s of seawater are mixed with about 700 - 800 l/s of cold groundwater and 100 - 200 l/s of warm water, yielding a total of 1500 - 1600 l/s (5400 - 5700 m3/h) for the main fish farm of the Silfurstjarnan Ltd. in Öxarfjördur. Electricity cost is high; at present, about 800 kW are required. The fish farm is equipped with two reserve diesel engines, both with the capacity to produce 750 kW in case of electrical failure.
A schematic diagram of the Silfurstjarnan Ltd. Fish farm in Öxarfjördur, NE-Iceland.
Whereas, only about 10% of the water resources are of geothermal origin, a cascaded usage of the warm water is of interest. The hottest water (35 - 37°C) is first used for domestic heating in the floors of the fish farm. For heating the houses, only a minor addition of heat from external sources is required, now provided by geothermal water from well AE-3. The hot water pipes then extend into a dense pipeline network in concrete pavement between the outdoor fish tanks, where it serves for snow-melting before being mixed with the water used for the fish.
Water is connected to the farm through several mains, made of PEH plastic pipes. On arrival to the farm, the three basic water types (cold/fresh, warm/geothermal and cold/sea water) are mixed in different ways to suit the different fish sizes/types. Before the mixtures are admitted to the tanks, de-aeration/aeration takes place in order to equalize nitrogen, which otherwise would reach supersaturation due to the mixing with warm water. Nitrogen in supersaturation may kill fish. Following de-aeration, water flows by gravity to the tanks. Flow rate to each tank is adjusted by valves to suit the respective biomass; this being primarily governed by the oxygen needs, but also by other factors such as CO2 level, self-rinsing of fish excrements and food leftovers, suitable water velocities for proper swimming exercise, etc.
In nature, fish is generally offered oxygen saturated waters. In tank farming, this is not possible, and certainly not without separate oxygenation. Since oxygen is the key factor, total water pumping can be reduced if oxygen levels, and thereby, reducing stress which again improves fish health and growth rate. The oxygen is partially produced on site by molecular sieves and partially bought liquified in bottles. The oxygen generating plant has a total capacity of 70.8 Nm3/h. The oxygen is introduced to the tank water mainly by pressure injection in the water supply prior to admittance to the tank. The principle behind is the following. The pressure on part of the water to the tank is increased by sending the water through a narrow port by an extra pump. The 2-in. port is at a top of a fiberglass cone with a 1.2-m diameter at the bottom. The water is released into the cone and oxygen blended into it at the top. With the pressure fail the water and oxygen mix. The water is then led from the cone into the tank through a 110-mm plastic pipe with a minimum length of 18 m to ensure complete mixing. In some of the smaller tanks, the oxygen is introduced by defusers at the bottom. The complete mixing of the oxygen in the water is of major importance for the optimal growth of the fish.
The tanks are circular, different in diameter and depth, from few m3 in volume up to some 1500 m3, the smaller tanks generally used for fingerlings and the biggest for fish in the 1 - 5 kg size. The smaller tanks are made of fiberglass; whereas, the bigger ones are assembled from precasted concrete elements, held together by tensional steel cable girths and surrounding soil (Figure 4). Installed fish tank capacity at present is about 15,000 m3 in the mail plant; but, additional tanks are under construction.
Some of the larger fish tanks at Silfurstjarnan fish farm (photo by G. Ó. Fridleifsson).
By introducing the inlet water from the oxygen injectors in a tangential direction and at variable rates with depth, water movement is optimized in order to provide a suitable swimming velocity and also a self-rinsing effect, where the bottom velocity is high enough as to sweep fish excrements towards the centrally located outlet, without stirring up the water. Tank effluent flows by gravity through traditional sewage piping system towards a settling pond, where the bulk of fish excrements and food leftovers settle for periodic removal. From the settling pond, effluent is channelled to the nearby Jökulsá glacial river.
Fish feed, partly made on site from fish trash, fish oil, vitamins and binding agents, and partly purchased ready-made, is dispersed in the form of pellets over the water level. Pellet size is chosen to suit fish size. About 85% of the feeding is automatic through feeders programmed to feed the fish at proper rate and at selected times of the day. The remaining 15% is done by hand depending on the appetite of the fish, which varies with weather and daylight, preferably at sunrise and sunset. Thus, it is possible to maximize the growth rate of the fish and at the same time, decrease the feed waste and water pollution.
Fish are transported from the smaller tanks to the bigger ones as size increases, usually every two months. This is done by a special fish pump which is basically a pressure vessel connected to the tank in question by a flexible tube. The vessel is then subjected to vacuum; whereby, water and fish will eventually fill it. Then the process is reversed, the vessel is now pressurized, a suction valve closes and a discharge valve opens for flow in the discharge tube, through which the fish is piped to a second tank, generally passing through a fish grader, or if the time is right, towards the finals at the processing plant. The graders are connected directly to computers, thus ensuring automatic control on the fish growth. The tanks are cleaned thoroughly before smaller fish are put into them again. One of the advantages of the 90°C hot water provided by the Öxarfjördur Heating Services is in rinsing and disinfecting.
The fish processing plant is 450 m2, including the offices of the Silfurstjarnan Ltd. Here the fish are slaughtered, gutted and processed (filet) for the needs of the different customers and packed with ice in styrofoam boxes before being sent to the markets. The ice is produced at the site.
Emergency alarms are connected to the most sensitive parameters for the fish to avoid accidents. Oxygen levels in the outlet water from each tank are monitored continuously, raising alarm if the values deviate out of present boundaries. Alarms are connected to the water system indicating if pumps go out. Every oxygen pressure injector is monitored contin-uously and the alarm is raised if it is not working properly. Finally, the temperature of the inlet water to the tanks is monitored raising alarm if it becomes too high.
THE PRODUCTION OF THE SILFURSTJARNAN LTD.
Two main species have been raised from the beginning: Atlantic salmon (Salmo Salar) and arctic char (Salvelinus Alpinus). The farming temperature is kept more or less constant the year around and accordingly, the demand for hot water diminishes during summers. The optimal temperature for salmon are at 8 - 10°C varying with size (Figure 5). The arctic char starts in colder water, 6°C, but is later on reared in the same 10°C water. It is worth mentioning that a small number of arctic char is kept in the tanks with the salmon (7% of the total fish number). In this form of cohabitation, the arctic charr lies at the bottom and lives mainly on leftover fish feed. Thus, the waste of fish feed is minimized. The salinity of the farming water is kept constant throughout the year at about 10 - 12 ppt (Figure 5), which is an increase from the 8 -10 ppt salinity used before. The increased salinity is one of the factors that has allowed steadily increased biomass per m3. The process from hatch to the market takes 30 - 35 months. Average weight of the salmon product is now close to 4 kg gutted weight (gutted and in some cases, filet fish), and the arctic charr product is about 1 kg. Hitherto, the plant has been free of any kind of fish disease, which to some extent relates to the superb water quality for fish farming. So far, not a single dose of medicine has been used. The fish is slaugh-tered four times a week, about 50 weeks a year (Figure 6).
A schematic layout of conditions and fish growth at Silfurstjarnan Ltd.
Slaughtering of fully grown salmon in the processing plant (photo by G. Ó. Fridlefsson).
Presently, the annual production is 900 - 950 tonnes or 50 - 60 kg/m3, which is a record production. Of this, salmon is about 80%. The steadily increasing production strongly relates to the stability in reari[blue]ng conditions that can be held due to the geothermal energy, which the siting of the fish farm was based on. Not only the temperature control, but also the purity of the groundwater and the salinity control are of fundamental importance to that can be added successful experiments in increasing the oxygen level in the farming water. These optimal growing conditions are manifested in various ways, such as the exceptionally high yield where only 1.05 kg of fish feed are needed to produce 1.00 kg of salmon. These figures do not include the arctic char kept with the salmon (about 2% of the fish weight in the tanks).
Marketing is done by the company itself. About 90% of the product is exported, mainly as a fresh fish product; but, some is marketed smoked. Most of the customers make use of the fish farm's capability of delivering the same size of fish in similar quantity throughout the year. Despite fierce competition, this has resulted in fairly high prices for the product, which in turn directly relates to the use of geothermal water.
The transport of fresh fish to the markets in America and Europe needs to be quick, and therefore, most of the product is exported by air. From slaughtering in this remote fish farm in NE-Iceland to the markets, the iced and packed product is driven about 700 km by trucks overnight to Keflavik airport in SW-Iceland, to be air-freighted to the markets the same day. The whole process only requiring about 1.5 days, up to 3 days at the most.
Or here where the Norwegians claim that they can export land-based technology:
http://www.norway.org/News/archive/1997/199705fish.htm
