SHURE FLOWtm TANKS FROM

GLOBAL AQUATICS

A vessel holding water is called a tank. However, just because a vessel holds water does not necessarily make it a good fish rearing habitat nor does it necessarily make it efficient for the operator to manage. Of all the aspects of modern aquaculture that researchers have studied, none has been more over looked than the size and configuration of the very vessel that the growing product has to call home until it is ready for market. We at Global Aquatics have never understood why people pay so little attention to this important part of a system design, especially since we have spent so much time developing what we consider to be the perfect design when efficiency and management are considered.

Small verses Large:

The key to successful operation of any fish system is "Total Control." This means control over each and ever animal in the tank and control over each and every gallon of water within that tank. Ask yourself these two questions; Why is it that even under the best of conditions a five acre catfish pond can only produce one pound of fish per 400 gallons of water, while even a poorly designed tank system can produce 1/2 pound of fish per 1 gallon of water? Why is it that when there is a total harvest of fish from a pond there is such a wide variation in the sizes of the animals even though they are all the same age and were placed in the pond at the same time? The answer to both of these questions is "Control", or in the case of the pond, "Lack" of total control. Now, one more question. What s the difference between a one acre pond and a 20,000 gallon tank? The answer is, "Some, but not much" What is the difference between a 20,000 gal fish tank and one that holds only 3,000 gallons? The difference is the same as night and day.

It is very important to remember that as a fish farmer you must manage two things at the same time, water quality and the fish. Obviously the less water you have right in front of you in a vessel, the easier it is to manage. there will be more positive water exchange from the inflow and less dilution. Thereby allowing for better water quality.

It also goes without saying that the more accessible the animals are to you the easier they are to manage as well. By managing the animals we are referring to the need to constantly sort the larger faster growing ones from the population at certain intervals during the growth process. This means that every so often the entire population of the tank must be separated into other tanks based on the size of the individual animals. The reason for needing to do this is because as in all animal populations a pecking order occurs whereby the larger, more aggressive animals dominate the rest of the group. When these dominate animals are removed from the tank and placed with others their same size, a new pecking order will develop within the the remaining population. It is because grading a pond is not possible that there is such a variation in growth sizes at harvest time. When grading a tank the faster it is accomplished the less stress is placed on the fish. When you have a large tank containing 25,000 or more animals it may not even be possible to grade this group and if it is attempted it will likely place some of this group under stress for as much as seven times the amount time it would take to grade the group in the smaller tank. Grading the fish is also a requirement for harvesting. Generally in an intensive system the fish are harvested on a continuous basis as they become market ready. Since we know that some of the fish will grow much faster than the others, it is necessary to be able to capture just the ones that are market size from a huge tank of ungraded animals without injuring the smaller that still need more growth time.

ROUND VS. RECTANGULAR

It must be remembered why anyone uses round tanks in the first place. A round tank is really just a cylinder holding the water. Because water exerts pressure equally in all directions when placed in a cylinder, round water vessels can be constructed very cheaply using the minimum thickness of materials. The advantages of this fact is, round tanks can be transported to a site and quickly set up. However, this convenience is the only quality of a round tank and this lends no particular advantage where production is concerned. It should be remembered that it is production that pays the bills and the fact that the tanks were easy to install should not be allowed to over shadow future performance. The most obvious first drawback to a round tank is they are space intensive. A round tank in a rectangular room means there is going to be a lot of wasted space in that room in the corners that the tank does not cover. Another draw back is the fact that a round tank has no difference in length or width, therefore water circulation can only occur in a circular motion. Many early designers use to explain that this circular motion was the most effective way to remove solids, because the vortex in the center acted like the vortex in a toilet. They obviously flunked out of physics class because the two vortexes are caused by different dynamic effects. In a toilet the vortex is caused by gravity. This occurs when the valve is flushed there is a sudden opening at the bottom of the bowl. As the water drops through the hole, gravity and the Earth's rotation takes control and causes the water to swirl around the void left by the water that has already escaped through the bottom. This causes a partial vacuum at that point and sucks everything into it. In a round tank the circular motion may resemble a toilet vortex, but instead of being caused by gravity and a
partial vacuum, it is being caused by water flow from a pump. This water flow is greater on the outer edge of the tank then in the center, therefore a certain amount of the solid waste in the tank will travel towards the center. However, the problem is, waste deposited along the outer edge of the tank may have to orbit the tank hundreds of times before it finally makes its way to the center. In the mean time it is being churned and homogenized the entire time and can cause water quality problems as it slowly dissolves. In a rectangular tank the water flow is generally in a straight line from one end to the other. This would mean that a solid deposited in one end of a 25 foot long tank can only travel 25 feet, and in one direction, before it hits the bottom solids trap. In most system designs the time required for the trip may only be a matter of minutes. Therefore the solid is removed in it's entirety before it has a chance to dissolve in the water column and cause water quality problems.

SO WHAT IS SO SPECIAL ABOUT GLOBAL AQUATICS' "STEEL CORE" S-99 TANKS?

The tanks design used in all Global Aquatics systems have very ridged design criteria concerning the ratio between length, width and depth. The bottom of the tank also has a unique shape design to allow for the horizontal flow of water to place a stratified area at the bottom to capture sinking particulate and move it towards the flush out area. These tanks are designed to work in harmony with the recirculated water inlet and oxygen injectors. The results are that there is an even and consistent water and oxygen flow distributed throughout all areas of the tank. There are several reasons why we feel our new "Steel core" tanks are better than either concrete or fiberglass, and we have done them both ways. One is cost. Global Aquatics has it's own fiberglass department which makes all of our other components so we know that fiberglass is more expensive than either steel or concrete when quality of construction and durability is considered. Global Aquatics' new S-99 "Steel Core" tank systems are fully coated with a thick covering of polyeurthane. This allows for much better temperature control within the water column. The problem with concrete we have found is that the acids of the water in a fish system slowly erodes the concrete and eventually it must be lined with some plastic substance. Another factor with the steel tanks is they are somewhat portable. If for any reason in the future the farmer wants to move them to another building or rearrange the current one, they can be moved with out any problems.

aquatic@iximd.com

All information found throughout these pages are the exclusive property of Global Aquatics Ltd. and may not be copied or distributed without the expressed written permission from the owners of this intellectual property.