Learn About Aquaculture
HERE YOU CAN LEARN ABOUT ALL ASPECTS OF AQUACULTURE
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The First Limiting Factor of Water Quality
Air breathing animals are used to air containing about 21 percent oxygen, whereas aquaculture is conducted in water containing less than .0001 percent oxygen (10 mg/L). With so little oxygen available in the best of conditions, it is apparent that knowledge of dissolved oxygen (D.O.), oxygen measuring and aeration equipment is very important to the aquaculturist.
If the oxygen level is too high, oxygen supersaturation can cause gas embolism, depress metabolism and inhibit respiratory enzymes, all of which can kill fish. If it is too low, the fish may not eat and may expend additional energy seeking oxygen. If lower yet, they can experience severe stress and, of course, death.
The diurnal oxygen cycle in outdoor ponds is show below. The delicate balance of dissolved oxygen vs the rate of oxygen consumption can shift rapidly with changing algal, temperature and wind conditions. In outdoor ponds, lower D.O. levels will occur in the summer because the rate of oxygen consumption increases as the temperature increases. Oxygen is THE MOST IMPORTANT thing to monitor. Monitoring and record-keeping will provide predictive knowledge.
Measure oxygen after altering water flowrates, feed rates, etc., and when developing new growing systems. No one can just look at the water and know the oxygen level. Oxygen can only be measured with a test kit or, more conveniently, with an oxygen meter.
Incorrect pipe sizing all too often causes unsatisfactory performance. Friction is the culprit. As the volume of air passing through the piping increases, the pressure required to deliver the air also increases due to friction (think of it as wind resistance). Since most aquaculture type aeration systems utilize low-pressure blowers, it is critical that nonrestrictive piping be used.
Pressure loss in air systems can be measured in inches of water ("H2O). The resistance to air flow caused by friction will decrease both the pressure to the air outlet (typically an air diffuser) and the volume of air delivered.
When designing the air system, it is important to add together all of the following: the maximum water depth to which the air is driven, the resistance in the air piping system and the resistance caused by the air diffuser. Our simplified chart can be used as a guide in determining the pressure loss caused by the piping. The blower pressure and air diffuser resistances are published in this catalog. If you are confused, don't worry. Call an AES technician at 407-886-3939 for help.
Example: 4 cfm need to be delivered a distance of 200 feet from a rotary lobe blower. The average line pressure is 3 psi. There are no odd twists or elbows that need to be considered. The minimum diameter of plastic pipe will be 3/4", causing 7.4" H2O resistance or pressure loss. The smaller 1/2" pipe would cause 24.6" of loss, which would probably be unacceptable. A 1" pipe, costing little more than the 3/4", might be an even better choice if there is the possibility of using more air in the future.
Anyone who has worked with fish for a while knows that if you don't plan ahead, you won't be in business for long. When it comes to life support, a backup blower could save your business.
The most crucial of life support requirements is maintaining an adequate oxygen level because it can be used up so quickly.
We always recommend having a second blower attached to the main air supply line, wired to come on if the primary blower fails for any reason. Both blowers must have check valves on them. A pressure switch is located between the primary blower and its check valve. When this pressure switch senses a loss of air pressure, it closes, causing an electric relay to start the backup blower (see diagram). The check valves keep air from being lost through the nonrunning unit.
Check valves must be able to tolerate high temperatures. Be sure the stand-by unit is on a different electrical circuit breaker.
The cost of fish food can represent 30 to 90 percent of the total cost of raising fish! In some situations (like indoor culture), feed must provide 100 percent of the complex nutritional requirements fish need. A less-than-complete diet will show up as poor feeding response, slow growth and/or disease problems. Poor water quality can also be caused by bad feed.
All feed should be used within the normal 6-month shelf life. Do not overfeed. In general, give fish a little less than they will eat (stop feeding them before they stop feeding).
Questions often arise about the size of fish food. Here are some suggestions for selecting food that is the right size for your fish.
- Some smaller hatchlings require food as small as 35 microns! Other hatchlings may be able to accept brine shrimp, large zooplankton or starter crumble from the onset. When in doubt, use the smaller size food.
- When changing food sizes, it is best to do so gradually by mixing the two sizes together, slowly converting to the larger size in a week or so.
- To learn more about feed sizes and feeding practices, consult the book Fish Hatchery Management (see Index).
Getting Started Guide:
- For fish under an inch in size, use brine shrimp, rotifers, powdered foods, flake foods or 00 starter crumble.
- To 2 inches: 1/32" granulated food, zooplankton or flake foods.
- 2 to 3 inches: 1/16" granules, zooplankton or flake foods.
As fish grow to 3 inches or more in length, food sizes become more uniform by species:
- 3 to 5 inches: 3/32" or 1/8" pellets.
- 5 to 10 inches: 3/16" to 1/4" pellets.
- 10 inches: 1/4" to 3/8" pellets.