Flow-through systems for Tilapia in Tank
Tanks come in a variety of shapes, but the most common forms are circular and rectangular. Raceways are rectangular tanks that are long and narrow. Variations of circular tanks are silos, which are very deep, and octagonal tanks. Circular tanks are very popular because they tend to be self-cleaning. If the direction of the inlet flow is perpendicular to the radius, a circular flow pattern develops which scours solids off the tank bottom and carries them to a center drain. Rectangular tanks are easy to construct but often have poor flow characteristics. Some of the incoming water may flow directly to the drain, short-circuiting the tank, while other areas of the tank maybecome stagnant, which allows waste to accumulate and lowers oxygen levels. For these reasons, circular tanks provide better conditions than rectangular tanks for tilapia culture.
Circular culture tanks may be as large as 100 feet in diameter, but common sizes range from 12 to 30 feet in diameter and from 4 to 5 feet in depth. Rectangular tanks are variable in dimensions and size, but raceways have specific dimension requirements for proper operation. The length to width to depth ratio should be 30:3:1 for good flow patterns. If the volume of water flow is limited, shorter raceways are better to increase the water exchange rate and prevent tilapia from concentrating near the inlet section where DO levels are higher.
An Open Letter regarding recent reports that low-fat fish like tilapia are unhealthy. (July 16, 2008)
Eating fish, especially oily fish, at least twice per week is recommended for heart disease prevention. Fish is low in total and saturated fats, high in protein and essential trace minerals, and contains long-chain omega-3 fatty acids (EPA and DHA). Oily fish rich in these healthy omega-3s include salmon, trout, albacore tuna, sardines, anchovies, mackerel and herring. Our omega-3 needs can also be met by eating less-oily (lower-fat) fish more often.
Tilapia and catfish are examples of lower-fat fish that have fewer omega-3s than the oily fish listed above, but still provide more of these heart-healthy nutrients than hamburger, steak, chicken, pork or turkey. Actually, a 3 ounce serving of these fish provides over 100 mg of the long chain omega-3 fatty acids EPA and DHA. Considering that this is about the current daily intake of these fatty acids in the US, even these fish should be considered better choices than most other meat alternatives. Since they are also relatively low in total and saturated fats and high in protein, they clearly can be part of a healthy diet.
US Department of Agriculture statistics indicate that farmed tilapia and catfish contain somewhat more omega-6 fatty acids than omega-3. Most health experts (including organizations such as the American Heart Association and the American Dietetic Association) agree that omega-6 fatty acids are, like omega-3s, heart-healthy nutrients which should be a part of everyone's diet. Omega-6 fatty acids are found primarily in vegetable oils (corn, soybean, safflower, etc) but also in salad dressings, nuts, whole-wheat bread, and chicken.
Replacing tilapia or catfish with "bacon, hamburgers or doughnuts" is absolutely not recommended.
William S. Harris, PhD, FAHA
Sr. Scientist and Director
Metabolism and Nutrition Research Center
Sioux Falls, SD