When a 200lb Atlantic halibut, who has faithfully supplied you with thousands of eggs each year, decides to retire from spawning, where do you send her? In the case of Scotian Halibut Limited, Bea and Kira were offered residence at the Maritime Aquarium in Norwalk, CT.
The retirement plan sounded great. But a transportation challenge remained. Being flatfish of considerable proportions (over 6’ long and 4’ wide), traditional transport tanks had openings too small for the fish. Given that the trip was over 1600km, the cost of building a tank, delivering the fish, and returning the tank and truck to Nova Scotia was starting to look prohibitive. The solution was to come up with a tank that could be built so cheap as to not need to return to Nova Scotia.
Materials were used for construction that could be found at any local hardware store. The surface area needed for Bea and Kira and company was calculated to be 5’ * 9’. A 30 inch water depth was used to maximise the water volume while remaining under the weight limit of the U-Haul that would be used for transport.
The base of the box consisted of 4” by 4” timbers at 16” centers covered with ¾” plywood. The frame used 2” by 4” lumber also at 16” centers, and also covered with ¾” plywood. The 2” by 4” pieces were installed so that a wall thickness of 2” (plus plywood) was created. The top was constructed in the same manner as the walls. The wall plywood was extended above the frame to accommodate the cover and prevent it from sliding off. The wall plywood also extended below the frame to the very bottom of the floor timbers for added stiffness.
The 2” wall thickness allowed for a layer of Styrofoam insulation to be nestled in between each timber. The box cover was likewise insulated. The floor was insulated in one full piece. The insulation was to prevent an accumulation of heat into the water during the 20 hour trip. Lining with Styrofoam also helped to lower the stress on the fish by deadening road noise, and providing a cushioned bottom to lie on.
Waterproofing was the next order of business. Three layers of 6 mil plastic were used to line the inside of the tank. Each layer was individually installed in the tank. Care had to be taken to fold the corners in such a way that the edges of the plastic were never below the top of the tank. The plastic was stapled in place.
The top itself was too heavy and awkward to be removed each time the oxygen had to be checked. A 6” by 6” access door was cut into the top. To get a good hold on the top when it had to be removed, two rope handles were located along each edge of the top. The handles consisted of two holes through the top. The rope was fed through each hole and knotted to prevent it from slipping back through the holes.
The total cost of building the box was under $500 (Canadian) and one day of work.
During the “test drive” with the tank full of water it was found that when braking, the water would surge enough to lift the top off the box and move it around. The “L” shaped brackets on the sides were quickly fabricated from ¾” plywood and installed. A 2” by 4” could be slid under each one to put downward pressure on the top and keep it in place. Steel angle brackets were also added at the top, middle, and bottom exterior of each corner to prevent them from pulling apart under the force of the water.
One sunny Nova Scotia day, Bea and Kira were loaded into the tank and were on the road by noon. By 8am the next morning the tank, truck, and precious cargo all arrived safely at the Maritime Aquarium; leak free, temperature steady, and well oxygenated.
Here are some things to keep in mind in case you need to build a similar tank.
A deeper tank requires stronger construction because of the head pressure of water.
Driving creates a lot of vibrations. So avoid using common nails. For the box described above we used only wood screws. Spiral nails could also work.
Due to the size and shape of the halibut brood stock moved in this tank, we were unable to build it such that a forklift could lift it when full of water. In our case, the box was loaded on the truck and then filled with water and fish were brought out to the truck. During unloading, the fish had to be unloaded from the truck by hand. Plan for this by leaving access room around the box, having a way to capture and handle the fish in an enclosed space, and a way to carry them up into a truck and down out of a truck. Or, build a smaller box that can be moved with a pallet jack and forklift and brought close to the tanks for loading and unloading.