By EMMA HOPKINS
LONDON, Ohio — All forms of agriculture require extensive knowledge, resources and equipment to be successful on a large scale. For production aquaculture, these come in the form of extensive knowledge of fish, water-based plants, water testing equipment – and perhaps a chemistry textbook.
Fish in natural settings maintain their ideal temperature, oxygen, pH, ammonia and nitrite levels because lakes and other bodies of water are their own biofilter – that is, they adhere to the food chain and convert waste material using bacteria. Such bodies of water are so large that they maintain the ideal water type for numerous types of fish.
In aquaculture, however, producers must regulate and simulate that water environment manually. Ohio State University’s aquaculture extension specialist, Matthew Smith, helps get people started raising fish, and lectured at last month’s Farm Science Review on the topic of water quality in fish production.
“By far the No. 1 reason people lose fish is because of water quality,” he said. “Fish are pretty hardy if you keep the water clean, and they’ll grow very fast for you, but the moment the water quality goes bad – it’s a great way to kill fish.”
Fish producers go into the business for different reasons and on different scales, but Smith said all systems require careful monitoring of water quality, especially when they are new.
In new systems, oxygen concentration must be higher in the water, bacteria need time to establish themselves and all quality parameters must be kept in “optimal” or “preferred” states to limit stress on the first fish in the tanks. Source water must initially be tested, as well.
Smith listed the parameters of temperature, dissolved oxygen and pH as critical when establishing an aquaculture system, and they should be tested daily. Biweekly, he said nitrite levels, total ammonia-nitrogen and un-ionized ammonia should be monitored; and monthly, alkalinity, hardness and others as needed.
“You’ll have to stock a lot of fish in there, and the way fish will tell you if they’re happy is they are either going to eat or they are going to die,” he pointed out. “You need your fish to be happy, because if they’re not happy, they’re not growing, and if they’re not growing, they’re not making money.
“That’s why I’m always pushing water quality issues, because if you make sure your fish are happy, they’re going to grow, and if you actually grow them and are a good marketer, you can sell them and turn a profit.”
Parameters include the following:
•Temperature (checked daily) – Unlike humans and most animals, the body temperature of fish is determined by the temperature of their water, so thermometers must be watched.
Smith said one way to do this is by putting sensors into tanks which send an alert to the producer’s cell phone when water goes above or below ideal temperature. Ideal temperatures vary depending on the breed of fish.
•Dissolved oxygen (checked daily) – Plants, bacteria, uneaten feed and fish waste all use up oxygen in the water, but fish need oxygen to survive, which is why dissolved oxygen levels must be tested and adjusted.
Microscopic plants produce oxygen for fish in natural and aquaculture production settings. Oxygen should be greater than 5 mg per liter at any given time.
•pH level (checked daily) – When pH levels are too strong, fish and plants are under stress because the amount of harmful ammonia increases.
•Nitrite (checked biweekly) – Nitrite is toxic to fish and must be kept below a specific level, determined by the fish, plants and bacteria in a system. One of the ways nitrite can be created is when ammonia is converted into it by bacteria.
•Ammonia (checked biweekly) – Ammonia is created in aquaculture system through uneaten feed and fish waste. In its un-ionized form, it is toxic to fish, while it is harmless in ionized form.
“Ammonia in the toxic form is a great way to kill fish,” Smith noted.
These parameters can be monitored using field test kits sold by many aquaculture companies. Fixing imbalances in water quality is usually done through water filtration using natural (biofilters) and manufactured filters.
Smith said before setting up an aquaculture system, producers should test their source water to be sure it doesn’t have higher or lower levels of chlorine, ammonia, iron, carbon dioxide or pH than needed. Contacting your water treatment plant so they can notify you when they change the water composition is a good idea.
Though it may seem like a much more tedious operation to conduct than, for instance, raising livestock, Smith said more than 100 aquaculture operations exist in the state of Ohio.
“People like ‘environmental sustainability,’ those sexy sort of terms, and farm fish for those sorts of reasons,” he explained. “Aquaculture systems are consistently recycling and reusing water. People like the fact that resources are cycling around; it’s a pretty self-contained system. Even in aquaculture ponds, the water is reused.
“It depends on where you are, but in the catfish industry, for example, you could go 10 or 20 years without fully draining that pond. It’s pretty water-efficient compared to a lot of other practices, even though the fish actually live in the water.”