Learn About Aquaculture
HERE YOU CAN LEARN ABOUT ALL ASPECTS OF AQUACULTURE
Cages may be the best method of fish culture in nonseinable water bodies. But there are peculiarities to cage culture that must be considered. As Bismarck said, "... it is better to learn from the mistakes of others."
- Seek help from people in your area who have successfully cage-raised the same species. Your State Aquaculture Extension Service is an excellent source of information.
- Your fish will be totally dependent on you for food and water quality. Still, no-wind periods are the worst without aeration.
- Build a cage that's easy to handle and harvest, and consider the possible need for sun shading.
- Consider feed waste potential and waste buildup below cages. Keep cage bottom at least one foot above lake bottom.
- Cage position is very important for water quality, feeding access, etc. Use an aerator or a current inducer for no-current periods.
- You may need to aerate the entire impoundment if it is, or will become, eutrophic as production (nutrient enrichment) continues.
- Inspect fish for mortalities, condition and, depending on where you are, loss to poachers!
- Inspect cages for turtle holes, overall condition, and biofouling (algae, bryozoans, invertebrates, etc.) that can restrict circulation.
- Be prepared for foul weather with heavy waves and strong currents. Also cloudy weather, plankton die-offs, overturns, etc.
With the variety of water pumps available today, selecting the ideal model for your application can be tricky. Following are a few useful definitions, helpful hints and conversion charts to aid in your decision:
Centrifugal Pump: Medium- to moderate-pressure, flooded-suction or self-priming pump. An impeller is used to "sling" water to the outside, pumping by centrifugal force.
Check Valves: Installed on pump outlet to prevent back siphoning when pump is off.
Flooded Suction: Water must enter pump by gravity.
Foot Valve: Installed on a pump inlet to prevent the loss of prime during nonoperational periods.
Freshwater Pumps: Freshwater pumps can be used with salt water for brief periods and experience only minimal corrosion. Rinse with fresh water after use.
Head: The amount of pressure a pump must work against during operation. Total head equals feet of vertical lift plus friction. The amount of head is an important value when sizing a pump correctly. One psi equals 27" of water.
Friction: The loss in pressure and volume that occurs when liquids travel through pipes, fittings and other restrictive elements of a piping system.
Gpm: US gallons per minute.
Pedestal Pump: A self-supporting pump mounted above a long shaft, with the motor above the water level and the intake below.
Pressure Curves: Motor overload can occur if pumps are operated below the lowest pressures depicted by the curves shown in the pumps' specifications. If your application does not have sufficient head pressure to stay within the curve, throttle the outlet with a valve or other restriction. Use an amp meter for guidance.
Propeller Pump: A submersible pump with a propeller, which draws water through a housing. Propeller pumps are usually high-volume, low-head.
Salt Water Compatible: Our salt water compatible pumps are rated for long-term, continuous duty with salt water. Little corrosion should occur within one year.
Spherical Pump: A silent pump that has only one moving part—an induction-driven impeller. Spherical pumps have no motor shaft, seals or bearings, making them virtually maintenance-free.
Trash Pump: A centrifugal pump that can pass large objects, including sand, gravel and mud. Often used for dewatering ponds.
Vertical Pump: A centrifugal pump mounted in a vertical direction. Vertical pumps usually have a long shaft with the motor mounted above water.
Airlifts are most efficient when moving water from one place to another within the water column. They become less efficient as the water is lifted higher above the surface. For our purpose here, we will split them into two categories: water-moving airlifts, and water-lifting airlifts, up to 4" in diameter.
Moving Water With Airlifts
Water is heavy when it is in the air, but weighs no more than the water around it when it is in the water. A water-moving airlift will translocate water using very little energy (compressed air). It just needs energy to accelerate and overcome friction. The more air that is injected and the deeper it goes, the more power available. An unconfined airlift doesn't even need a pipe. An air diffuser moves a lot of water within its mass of bubbles.
When trying to lift water to a high level, a water pump is simpler and more efficient than an airlift. However, raising water only slightly above the surface can be done easily and economically with compressed air and an airlift pipe.
- Do not use an air diffuser. Large bubbles work best, as they reduce water slippage. Air-injecting collars can improve performance slightly on short pipes but, typically, they are not worth the installation and maintenance difficulty.
- Smaller pipe diameters work best. If more water is needed, use multiples of small diameter pipes. Also, a sweep works better than an elbow.
How Does It Work?
- Water in the pipe is displaced with air, making the total weight within the pipe less than the weight outside the pipe.
- Since water seeks its own level by virtue of its weight (and its fluid nature), it will get pushed up an airlift pipe because the weight is less there (lower pressure).
- Ever hear the phrase, "Wind doesn't blow, it sucks?" It's true. The direction of flow is from high pressure to low.
Did you know that for every 1 lb of oxygen consumed by fish they exhale 1.38 lbs of carbon dioxide? Carbon dioxide does cause problems in recirculating systems without aeration or degassing. This can be the case, for example, where pure oxygen is used in place of aeration. Carbon dioxide must be removed, or it can build up to dangerous levels…dangerous to the fish and to humans if the fish are raised in a closed building.
Here are some numbers to keep in mind. Oxygen is about 20.9% of the air and, because it is only slightly soluble in water, it becomes saturated at a level of about 9 ppm at 68°F (20°C). Carbon dioxide is .033% of the air and is saturated in water at about .5 ppm (the ratio is higher because it is more soluble than oxygen). The comparative concentration of these two gases in blood is similar to that of water. Therefore, a lot of carbon dioxide in the water means there will also be a lot of carbon dioxide in the blood of the fish. An excess of 5 ppm carbon dioxide in the water will affect the ability of the fish to breathe.
If intensive aquaculture operations are being conducted outdoors, a splash aerator or aeration with air diffusers will drive the carbon dioxide into the air. If the operations are in a closed building, very high levels of carbon dioxide can accumulate in the air (we've seen levels exceeding 4,000 ppm in the air in closed aquaculture facilities!). It then has to be removed from the building.
Air ventilators can also remove a lot of heat along with the carbon dioxide. We suggest that carbon dioxide be stripped with a degassing column that is ventilated to the outdoors. Outdoor air can be drawn directly into the bottom of the degassing tower, forced up through the downflowing liquid, then directed back outdoors separate from the inlet. In cold weather, there will be a significant cooling effect on the water because it is being degassed through cold, dry air. A simple air-to-air heat exchanger will help.