PAES W.A.T.E.R. Updates


Fish Behavior ... Or Not Behaving? |A Closer Look at Biological Filtration |Biological Filtration | Hybrid Striped Bass and Water Hardness | PAES W.A.T.E.R. Center Oxygen Supply | Fish Swimming in Two Directions | Raises & Harvests Next Cohort of Fish | Tilapia Sampling in System D


Fish Behavior ... Or Not Behaving?
May 16, 2017

Fish Behavior ... Or Not Behaving?

To get an idea of how fish behave in under-crowded conditions, take a look and study for a few minutes the behavior of the fish at: http://paeswater.com/live-events.html These fish are large size tilapia, primarily a male population, and you can notice the interactions and conflicts between pairs of fish. Watch for a few moments and you will see individual fish challenge one of their tank mates, biting, swimming alongside, chasing, and circling with their targets. This behavior is a challenge for territory, and it is occurring more frequently because this tank is being harvested, the numbers of fish are declining, and they have more space to ‘misbehave’. Under normal culture conditions and stocking numbers, the fish are crowded enough that this behavior is removed, or more rarely seen. With higher numbers, fish are simply too crowded to be able to fight with each other, and they settle down and more peacefully coexist, waiting for the feeder to arrive with a new meal…

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A Closer Look at Biological Filtration
May 16, 2017

A Closer Look at Biological Filtration

In the last post, the general concept of biological filtration was examined. Now, in more detail, we discuss the all-important process of biofiltration in Recirculating Aquaculture Systems (RAS). Previous photos showed a biological filter that is classified as a Moving Bed Bio Reactor, or MBBR. In this type of biological filter, the filter media is constantly mixed and moved by air, creating an environment to promote the growth and development of beneficial bacteria. These bacteria are of two types: (1.) Nitrosomonas species, and (2.) Nitrobacter species. These beneficial bacteria are located all over the world, and are important in the Earth’s nitrogen cycle. In the MBBR of our systems, we actively culture these bacteria to help in converting the ammonia waste from the gills of the fish that we are growing. Above is a closer look at the biofilter elements, plastic shapes that provide a large amount of surface area on which bacteria can grow. Brand new, clean material is on the left, and material with its colored coating of live bacteria, on the right. The MBBR is designed and operated to contain the biofilter elements and keep them moving, to provide healthy conditions for the bacteria to grow. Biofilters are critical components of RAS!

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Biological Filtration
May 2, 2017

Biological Filtration

Well-designed Recirculating Aquaculture Systems (RAS) rely upon filtration of the water to remove waste products of the cultured organism. With RAS that are designed for production, high daily feed rates are usually reached, resulting in waste products from the fish that must be removed or converted. Filtration that occurs in RAS is generally classified as one of two different types: (1.) mechanical filtration (removal of solid waste), and (2.) biological filtration (conversion of nitrogenous waste). Consider biological filtration and why it is needed. One of the wastes that fish produce is excreted, or removed from their bodies, by diffusing it out of their gill surfaces. This waste is in the form of ammonia, chemically written as NH3. This ammonia is a waste product of fish feeds that contain protein. Ammonia is released from their gills, and becomes dissolved in the water in which the fish live and grow. At higher concentration, ammonia can be toxic to fish, so it must be removed. In RAS, a component is included in the system that provides a place for beneficial bacteria to live, the biological filter, or biofilter. These living, naturally occurring bacteria live in the biofilter and constantly convert ammonia that fish produce to a less toxic form that we will discuss more in detail in future posts. The live bacteria grow, reproduce, and constantly renew themselves. Above are two photographs of the same biofilter in PAES W.A.T.E.R. Center, on the top is the biofilter with new, clean biofilter media, and on the bottom is the same biofilter with the biofilter media colonized with bacteria, growing on the filter elements and converting the ammonia as the water constantly flows through. More on biological filtration to come…..

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Hybrid Striped Bass and Water Hardness
April 25, 2017

Hybrid Striped Bass and Water Hardness

Growing and handling Hybrid Striped Bass (HSB) in Recirculating Aquaculture Systems (RAS) requires much attention to water quality parameters. HSB are a relatively hardy fish and suitable for culture in RAS, but there is one water quality parameter that is critical to maintain for good HSB health--the calcium hardness of the water. Total hardness is the measure of both calcium and magnesium dissolved in the water, however, magnesium hardness is not as critical to maintain as calcium hardness for HSB. Calcium in this form is used for osmoregulation (adjusting the amount of water in the body tissues), in muscle contraction, and in transport across cell membranes. Our technicians working with the HSB in PAES W.A.T.E.R. Center System E, which is on live video camera at http://paeswater.com/live-events.html, test calcium hardness at least twice per week, and maintain it greater than 250 milligrams per liter (250 ppm) at all times. This level of calcium hardness makes the fish more resistant to the stress of handling when they are sampled for size, moved between tanks, or transported alive. To adjust calcium hardness, our technicians add granular calcium chloride (CaCl2), which is easily dissolved in the water. In areas of the United States where there is successful pond culture of HSB, such as eastern North Carolina or in Arkansas, the water that is pumped from wells into the ponds is high in calcium hardness, allowing HSB aquaculture to develop in those locations.

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PAES W.A.T.E.R. Center Oxygen Supply
April 18, 2017

Oxygen Supply

Recirculating Aquaculture Systems (RAS) require either aeration or oxygenation to support the fish population. At higher fish densities and higher feed rates, there is a greater oxygen demand for the system, and aeration, with the use of air only, cannot provide the quantity of oxygen required to maintain dissolved oxygen (D.O.) concentration. In these cases, supplemental oxygen must be provided. In PAES W.A.T.E.R. Center, we have created an oxygen supply system for the entire building. Three sources of oxygen are used: (1.) electrically powered oxygen generator, (2.) high-pressure oxygen cylinders, and (3.) liquid oxygen storage cylinders, or ‘dewars’. These three oxygen sources are connected and managed to assure an uninterrupted oxygen supply to the building and our systems. Oxygen is injected into saturators that dissolve oxygen in the water supplied to the fish tanks, and oxygen is also available to maintain the D.O. concentration in the event of electrical power outages, or during sampling and harvesting activities. With high fish density and high feed rates that these systems experience, in the event of an interruption of the oxygen supply, D.O. levels can decline rapidly enough for fish to begin to die within 20 minutes. Take a look at our Live Video Camera at http://paeswater.com/live-events.html, and note the small tubes around the perimeter of the tank to supply backup oxygen to diffusers in the tank.

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Fish Swimming in Two Directions
April 13, 2017

Fish Swimming in Two Directions

In PAES W.A.T.E.R. Center, while the water is very clear in Tank E1 (due to withholding of feed for purging and harvest), notice the swimming patterns of the fish. On our Live Video Camera at http://paeswater.com/live-events.html, you see fish swimming in two directions. Looking down on the tank, there is a current being created by the incoming water in a clockwise direction. This current is common in well-designed RAS and helps to move solid waste to the center of the tank, where it can be removed at the drain. The upper layer of fish is swimming with the current (clockwise), while the group of fish nearer the bottom is swimming against the current (counter- or anti-clockwise). Fish behavior of swimming against the current is natural behavior, orienting themselves upstream so that they can benefit from any food being moved toward them by currents and flow. In Tank E1, fish swimming with the current are resting, expending less energy, as are those fish gathered near the center of the tank where the current is slower. If you watch for a while, you will notice fish changing direction, moving from one layer to the other.

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PAES W.A.T.E.R. Team Raises & Harvests Next Cohort of Fish!
April 7, 2017

PAES W.A.T.E.R. Team Raises & Harvests Next Cohort of Fish!

On Friday, April 7, our PAES W.A.T.E.R. team harvested and sold about 250 pounds of live Hybrid Striped Bass (HSB). These fish had been purged in preparation for sale and live transport. Purging fish is a common practice in aquaculture in which feed is withheld for a period of time before moving fish, to allow the fish to empty their digestive systems, improve their flavor, and create less waste during live transport. An additional 600 pounds of HSB were moved from Tank E1 to begin the purging process for upcoming sales. Average size of the fish was 726 grams each, or about 1.6 pounds. These fish came to us in August 2016, and are on day 247 of this growout trial. Tank E1 is the main tank of our coolwater demonstration system, and is visible on our Live Video Camera at: http://paeswater.com/live-events.html.

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Tilapia Sampling in System D

November 16, 2016

Tilapia Sampling in System D

Check out some photos from our Tilapia sampling at PAES W.A.T.E.R. on November 15, 2016. The tilapia in System D weigh on average 720 grams (1.59 pounds). They have reached their target weight and are ready for harvest. We will update everyone on when the harvest is going to happen!

Please view more information for System D:
D1 = 2,798 fish @ 721 g (1.59 lbs) = 2,017 kg (4,437 lbs)
D2 = 1,015 fish @ 676 g (1.49 lbs) = 686 kg (1,509 lbs)

Green text is average weight of fish in each tank. Blue text is the total biomass is each tank.

Tilapia Sampling in System D

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