Production management tilapia in tank
The highest mortality of the production cycle (about 20 percent) occurs during the fry rearing stage. Much of this is due to predation. As the fish grow and become hardier, mortality decreases significantly at each stage so that no more than 2 percent of the fish are expected to die during final growout.
Fry are given a complete diet of powdered feed (40 percent protein) that is fed continuously throughout the day with automatic feeders. The initial feeding rate, which can be as high as 20 percent of body weight per day under ideal conditions (good water quality and temperature: 86°F), is gradually lowered to 15 percent by day 30. During this period, fry grow rapidly and will gain close to 50 percent in body weight every 3 days. Therefore, the daily feed ration is adjusted every 3 days by weighing a small sample of fish in water on a sensitive balance. If feeding vigor diminishes, the feeding rate is cut back immediately and water quality (DO, pH, ammonia, nitrite) is checked.
Feed size can be increased to various grades of crumbles for fingerlings (1 to 50 grams), which also require continuous feeding for fast growth. During the growout stages, the feed is changed to floating pellets to allow visual observation of the feeding response. Recommended protein levels are 32 to 36 percent in fingerling feed and 28 to 32 percent in feed for larger fish. Adjustments in the daily ration can be made less often (e.g., weekly) because relative growth, expressed as a percentage of body weight, gradually decreases to 1 percent per day as tilapia reach 1 pound in weight, although absolute growth in grams/day steadily increases.
The daily ration for adult fish is divided into three to six feedings that are evenly spaced throughout the day. If feed is not consumed rapidly (within 15 minutes), feeding levels are reduced. DO concentrations decline suddenly in response to feeding activity. Although DO levels generally decline during the day in tanks, feeding intervals provide time for DO concentrations to increase somewhat before the next feeding. Continuous feeding of adult fish favors the more aggressive fish, which guard the feeding area, and causes the fish to be less uniform in size. With high quality feeds and proper feeding techniques, the feed conversion ratio (fish weight gain divided by feed weight) should average 1.5 for a l-pound fish.
Total production levels range from 3 to 6 pounds/ft3 of rearing space and 6 to 17 pounds/gallon/minute of flow. Monthly production levels range from 0.4 to 0.6 pounds/ft3. The higher production levels are generally obtained in flow-through systems. Production can always be increased by increasing the inputs, but this may not be economical
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