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Aquaculture Sample Lesson
AC012 Combining Aquaculture with Hydroponics
In a natural pond setting, fish, bacteria and plants all work together to provide nutrients and waste disposal for each other. The diagram shows the ammonia/nitrogen cycle that is key to this ecosystem: Here's how it works. Fish live in their own bathroom. They can't help it, they have nowhere else to go. And fish waste is mainly ammonia, that evil smelling stuff you clean windows with. If you feed the fish too much, and their ammonia laden wastes build up, the fish do the same thing that you would do if immersed in an ammonia bath...they die. The same thing happens if you overfeed the fish and uneaten food remains in the tank. The natural breakdown of the food will kick the ammonia level through the roof (fish tank?), and poof, dead fish.
Now, fish have been doing fine for eons. So obviously, something is taking care of the nitrites. This time it's another bacteria, Nitrobacter. These wonderful little beasties feast on nitrites, they eat it like we would feast on ice cream on a hot afternoon. And when their bodies are done, they excrete nitrates. Nitrates are 10-100 times less dangerous to the fish. Still, if the levels of nitrates ever manages to get too high, it can still kill the fish. Luckily, nitrates are the form of nitrogen that plants love to eat. Not just one or two types of plants, nearly all plants love nitrates. And, next to carbon dioxide, nitrogen is the highest chemical on the plant's food list. Without nitrogen (nitrates), the plant won't grow. Give a plant plenty of nitrogen (along with plenty of light, water, CO2 and about 13 other tinier amounts of other elements), and it grows big and strong. It also locks that nitrogen up in its leaves and stems, removing them from the food chain. AN AQUAPONIC SYSTEM combines aquaculture and hydroponics to provide all three of the necessary parts of the ammonia/nitrate cycle. The three parts are: fish to produce the ammonia, bacteria to break the ammonia down to nitrates and plants to feed on the nitrates to create fish food to start the cycle all over again. Aquaponic systems are semi-experimental. The whole field of aquaponics is brand new; there are probably less than 500 systems in existence in the world. Hydroponics and aquaponics are true recycling systems that reuse their water and nutrients. Groundwater is not polluted. There is no nutrient runoff. They use less than 1/10th the fertilizer of traditional agriculture and 1/100th the water of traditional aquaculture. Plus, these high-yielding systems outperform traditional agriculture by up to 30 to 1. It will be exciting to see how aquaponics develops in the future. What is AQUAPONICS? 1. Aquaponics is a semi-closed loop ecosystem. 2. Aquaponics is a combination of aquaculture (raising fish in a controlled environment) and hydroponics (growing plants without soil, providing the nutrients to the plants mixed into the water fed to the plants). 3. Aquaponics is a man-made version of Mother Nature's pond, stream and field ecosystem. In the simplest classroom-sized aquaponic system, the fish live in a standard fish tank. A pump that sits in the tank with the fish pumps the water (and fish wastes) up to a series of troughs sitting nested into the top of the tank. As the water sprays out of the pipes leading from the pump, it picks up oxygen and flows down the troughs. Plastic pots sitting in the troughs contain blocks of rockwool, a sterile growing media similar in appearance to fiberglass. The water and dissolved fish wastes feed up into the rockwool by capillary action, where bacteria are cultivated. The bacteria do their thing on the ammonia and feed plants like lettuce or basil that are also growing on the rockwool cube. The cleansed water then flows down the trough and pours into the fish area in the tank, completing the cycle. More complicated and efficient aquaponic systems use the same basic concept, but they are more efficient at gathering the fish wastes, have several types of hydroponic systems to handle separating the fish wastes into suspended versus dissolved solids, have more elaborate hydroponic systems for nitrate removal, and perhaps have other systems to maximize the growth of bacteria and removal of nonorganic materials from the water. They also may contain automatic monitoring systems, backup pump systems, auto feeding systems for the fish and other systems to maximize the growth of the plants. An aquaponic system is NEARLY a total recycling system. Your plants can be fed directly to the fish, the fish wastes feed the bacteria, and the bacteria wastes feed the plants. Great! But FISH GROW! As the fish grow they consume energy (matter) that is removed from the recycling system. The energy, in the form of various nutrient elements, needs to be restored in the system for continued good growth. You need to FEED THE FISH! An aquaponic system isn't overly choosy on the variety of fish inhabiting its tank. What it is choosy about is the nutrient loading and temperature of the water. The core of the system is the bacteria. Bacteria perform best when they are warm; nitrating bacteria like it best around 75-80 F. Bacteria adapt to nearly any nutrient loading, but since the bacteria take literally days to adapt to changes in their environment, constant changes in volumes of feed will wreck havoc on your bacteria population. If the fish are little or few in your system, there aren't enough nutrients (wastes) flowing through the system to sustain good plant growth. But the system has to be designed for waste removal at the largest size that the fish will reach. Too little fish = too little "wastes." What to do? FEED THE PLANTS! To fertilize the plants you can introduce nutrients in two ways: in the water or on the leaves. Putting nutrients in the water with the fish is the most efficient. The problem is that nutrients are not an "approved" additive for food grade fish in a hydroponic system. You can legally add nutrients to a catfish or bass pond, but not in a recirculating system. The other way of getting nutrients into a plant is by foliar feeding the plant, spraying water and nutrients onto the leaves of the plant. Fans may be needed to prevent growth of mold or other diseases on the plants. Plants need more than water and nutrients (which the aquaponic system supplies in abundance). They need light! Up to their light saturation point, any time you increase the amount of light a plant gets, you increase the growth rate. Ten percent more light gives eight percent more growth. The more plant growth, the better the nitrate removal of the system. But remember, those extra lights produce heat. Too much light and heat in a small area can be deadly. ** Much of the information in this lesson was provided courtesy of Scott Jones of H/A Technologies, P.O. Box 777, Princess Anne, MD 21853. INTERNET RESOURCES:
** Aquaponics Journal - Information and photos about aquaponics
** S & S Aqua Farm EXERCISES: 1. Does an aquaponic facility use intensive or extensive production methods? Explain your answer. To find out more about intensive and extensive production methods, review AgEdNet.com lesson AC009 Exploring Aquaculture Systems. 2. Why do you think aquaponics is not used more widely in aquaculture production? Give at least three reasons. 3. Use a search engine such as Google.com on the internet to look for references to aquaponics. Write a brief description of what you find. You might start with the sites listed under Internet Resources. TEST:
1. Nitrobacter bacteria need which of the following to grow?
2. Nitrosomonas bacteria thrive on which of the following?
3. Plants need which of the following for healthy growth? 4. The three necessary living elements in an aquaponic system are __________, __________ and __________. 5. Aquaponic systems are in common use today. TRUE or FALSE?
---------------------------------------------------------------------------- END STUDENT SECTION AC012 Combining Aquaculture with HydroponicsTEACHER'S GUIDEOBJECTIVE: The student will understand how fish, bacteria and plants work together in the ammonia/nitrogen cycle which can be used in aquaponics. PREPARATION: Contact your regional aquaculture center or state aquaculture extension specialist to find any aquaponic facilities near you. Find out how these ideas are working in practice. INTERNET RESOURCES:
** Aquaponics Journal - Information and photos about aquaponics
** S & S Aqua Farm IMPORTANT TERMS: ammonia/nitrogen cycle, Nitrosomonas bacteria, Nitrobacter bacteria, nitrites, nitrates, ammonia, aquaponics, rockwool, hydroponics, bacteria. EXERCISE ANSWERS: 1. The answer is extensive production methods. The student should include such reasons as the fact that many outside inputs are added. The inputs might include: electricity for lighting and pumping, fertilizer, feed, labor to run the system, plants, etc. 2. Answers will vary, but might include the following: still experimental, complicated procedures, everything must be balanced in the cycle of production, temperature control may be needed and that is expensive, recirculating systems on a big scale may be impractical, specialized training needed for workers. 3. Student answers will vary according to what resources they discover. TEST KEY:
1. Nitrobacter bacteria need which of the following to grow? Correct answer: B. Nitrites
2. Nitrosomonas bacteria thrive on which of the following? Correctanswer: A. Ammonia
3. Plants need which of the following for healthy growth? Correct answer: C. Nitrates 4. The three necessary living elements in an aquaponic system are fish, bacteria and plants. 5. Aquaponic systems are in common use today. TRUE or FALSE?
FALSE. Aquaponic systems are still new; there may be only about 500 in existence. END
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Luckily, nature provides a way to eliminate the deadly ammonia hazard. Certain bacteria eat ammonia, they LOVE it. The most voracious ammonia-eating bacteria are called Nitrosomonas bacteria. They gobble the ammonia down, use it to fuel their tiny bodies and give off wastes full of nitrite nitrogen. Most fish can handle up to 10 times as much nitrites as ammonia. BUT...if the nitrites become too strong, there goes the fish, belly up again.
