There is an increasing demand for fish while native stocks are being stressed by over fishing. The obvious solution is to raise fish. There are difficulties of fish parasites and disease outbreaks in close confinement when they are raised in ocean pens. An alternative is to build large enclosed fish-rearing tanks.
For 1000 m width and allowing 200 m for a center portion for early growth tanks and support equipment and facilities, there would be 16 rings. The average diameter would be about, 1000 + 200 = 1200/ 2 = 600 m for a circumference of 1800 m. With a depth of 20 m; 1800 X 20 X 20 X 16 rings =
12 000 000 cubic meters, m3. The question then becomes how tightly to pack the fish.
If the fish are stocked at 1 / 40 the volume, apparently tighter packing is possible, and one assumes that the fish double in size each year over a 3 year growth cycle, the fish would need 1 volume in year 1, 2 volumes in year 2, and 4 volumes in year 3, actually there would be somewhat more available for year 3 as the fish do not spontaneously double in size, or 4 / 7, 57%, would be harvested, so
12 000 000 X .57 / 40 = 170 000 metric tonnes of fish harvested annually. Allowing a net yield of 50% weight for fillets, = 85 000 000 kilograms of salable weight annually.
For a structure of 1000 m by 1000 m, if the construction costs are $5000 / square meter, m2, the total cost would be $5 000 000 000 ($5 billion). If financing is at 5%, the structure should last at least 50 years,so amortization could be adjusted for that period, the finance costs would be $250 000 000 /yr or $3 per kilogram of salable fish.
There was a report some 10 years ago that said fish processors in Norway were shipping fish to China for processing before returning them for sale in Norway. The claim was that shipping and processing in China cost over $1.50 / kg, while Norwegian processing cost some $3.00 / kg. As fuel prices rise, the cost of shipping rises and the total cost of shipping and processing.
Machines have been built as test equipment that can automatically; cut off fish heads and tails, open fish, clean out fish, remove fish bones and even peel off the skin, the latter, I believe, aided by rapid heating of the skin with steam before removal. If there is a constant processing of fish, the cost of maintaining such automatic machines could be met and a large part if not all of the cost of the fish tanks could be offset by the cost savings of the automatic processing.
At C, is shown the feeding cart, c. The cart would travel around a circular set of tracks at the edge of the tank. It would spray the food across the tank for the fish to feed. One of the complaints of pen raised fish is that the flesh is flabby from having no exercise for salmon and tuna. The cart allows the fish to exercise by chasing their food. For slow moving fish, such as cod, the cart might move at 3-5 kilometers per hour, kph, for salmon it might move at 10-20 kph to make them run. The cart would be refilled by a hopper, h, that would move on overhead rails. There would be 2 carts, 1 would be feeding the fish while the other is refilled. As the first approaches the loading station, the second would begin moving forward while the first stops and is refilled.
If the fish are packed densely, there would be the need for frequent changes of water as fish digest protein and excrete ammonia. This would require extensive piping beneath the tanks.
By enclosing the tanks with a roof, there is no danger of bird predation and a reduced risk of pathogens moving into the water. In addition it would allow fish of different temperature regimes to be raised in one location.
By isolating the fish in tanks and raising the feed under controlled conditions, it should be possible to raise low mercury predators, such as tuna.
At I, is illustrated the movement of fish between tanks. 2 nets would be lowered into the interior tank after the exterior tank has been emptied of fish. 1 net would move forward past the tunnel connecting the 2 tanks. The tunnel doors would be opened adn a guide net, set at a diagonal across the interior tank, would be place just past the tunnel. The net behind the tunnel would be raised, and the one in front would sweep progressively around the tank, forcing the fish into the outer tank. Once this is completed, it would be repeated for the next inner tank.
At D, is shown one possible solution. A mandrel of metal that has a coefficient of temperature expansion greater than glass would be place on supports. An extrusion form would deposit molten glass around the mandrel. Then another section of the extrusion device would vapor deposit aluminum onto the glass tube over about 1/3 of its circumference. This aluminum would be placed on the lower side of the tube when mounted in sunlight to reflect light that has not been intercepted by the algae back into the tube to give the algae another chance to utilize it. Then another layer of glass could be deposited ocer the aluminum to protest it.
It might be necessary to have an outer slip form slide over the lower surface of the tube while being formed to prevent excessive sagging of the glass.
The mandrel would be slid horizontally after the full tube is formed and slowly cooled. When the glass has solidified, the mandrel could be withdrawn, although this would involve dragging it over the interior surface of the glass, so care would need to be taken.
The tube might have an interior diameter of 4-5 m and be 200 m long.
To estimate the size of the field for the tubes: 170 000 000 kg of fish X 1000 gm/kg X 4 Calories per gram of protein or carbohydrate, fat is 8 Calories, but 1 food Calorie is actually 1 kilocalorie or 1000 calories X 4 joules / calorie = 2700 X 10^12 joules per year or 7 X 10^12 joules per day. But fish need at least 1 1/2 calorie of food for each calorie of fish, = 10 X 10^12 joules /day.
Sunlight at noon directly under the solar high point, equator, is over 1 kilowatt/m2. Allow for at least 10 hours of sunlight X 0.7 to allow for the average solar elevation X 3600 seconds per hour X 0.7 to allow for cloud cover = 18 000 000 watt-seconds or joules / m2.
Dividing 10 X 10^12 by 18 X 10^6 = 550 000 m^2. However plants are not very efficient in using sunlight. Terrestrial plants do not exceed 5% conversion of solar energy into plant energy. 5% would require 20 times or 11 square kilometers.
The parts of the fish not sold, about 1/2 could be fed to other fish, that would be a 1/3 reduction in calorie needs, but the algae would be mostly fed to an intermediary such as krill or herring and that would require more food. This is what would probably kill it, the cost of all those glass tubes and the plumbing they would require.
If this could be afforded, the glass of the tubes would be cleaned every night by a robotic scrubber that would move through them with brushes that cover the entire interior surface.
F, shows the central fish tanks with arrays of glass tubes and production facilities connected to it. The fish would be moved into the separate production units immediately after harvesting.
G, shows the harvesting ring, a smaller ring at the outside.
H, shows the capture method of forcing the fish to a central conveyor belt where they are raised and stunned by electricity before moving into the processing equipment.
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