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Feeding behaviour for tilapia and nutrition requirements

Tilapia ingests a wide variety of natural food organisms, including plankton, some aquatic macrophytes, planktonic and benthic aquatic invertebrates, and larval fish, detritus, and ecomposing organic matter. With heavy supplemental feeding, natural food organisms typically account for 30 to 50 percent of tilapia growth. (In supplementally fed channel catfish only 5 to 10 percent of growth can be traced to ingestion of natural food organisms.) Tilapia are often considered filter feeders because they can efficiently harvest plankton from the water. However, tilapia does not physically filter the water through gill rakers as efficiently as true filter feeders such as gizzard shad and silver carp. The gills of tilapia secrete a mucous that traps plankton. The plankton-rich mucous, or bolus, is then swallowed. Digestion and assimilation of plant material occurs along the length of the intestine (usually at least six
times the total length of the fish). The Mozambique tilapia is less efficient than the Nile or Blue tilapia at harvesting planktonic algae. Two mechanisms help tilapia digest filamentous and planktonic algae and succulent higher plants: 1) physical grinding of plant tissues between two pharyngeal plates of fine teeth; and 2) a stomach pH below 2, which ruptures the cellwalls of algae and bacteria. The commonly cultured tilapias digest 30 to 60 percent of the protein in algae; blue-green algae are digested more efficiently than green algae. When feeding, tilapias do not disturb the pond bottom as aggressively as common carp. However, they effectively browse on live benthic invertebrates and bacteria-laden detritus. Tilapias also feed on midwater invertebrates. They are not generally considered piscivorous, but juveniles do consume larval fish. In general, tilapias use natural food so efficiently that crops of more than 2,700 pounds of fish per acre (3,000 kg/ha) can be sustained in well-fertilized ponds without supplemental feed. The nutritional value of the natural food supply in ponds is important, even for commercial operations that feed fish intensively. In heavily fed ponds with little or no water exhange, natural food organisms may provide one-third or more of total nutrients for growth. In general, tilapia digest animal protein in feeds with an efficiency similar to that of channel catfish, but are more efficient in the digestion of plant protein, especially more fibrous materials. Tilapia requires the same ten essential amino acids as other warmwater fish, and, as far as has been investigated, the requirements for each amino acid are similar to those of other fish. Protein requirements for maximum growth are a function of protein quality and fish size and have been reported as high as 50 percent of the diet for small fingerlings. However, in commercial food fish ponds the crude protein content of feeds is usually 26 to 30 percent, one tenth or less of which is of animal origin. The protein content and proportion of animal protein may be slightly higher in recirculating and flow-through systems. The digestible energy requirements for economically optimum growth are similar to those for catfish and have been estimated at 8.2 to 9.4 kcal DE (digestible energy) per gram of dietary protein. Tilapia may have a dietary requirement for fatty acids of the linoleic (n-6) family. Tilapia appear to have similar vitamin requirements as other warmwater fish species. Vitamin and mineral premixes similar to those added to catfish diets are usually incorporated in commercial tilapia feeds. The feeding behaviour of tilapia allows them to use a mash (unpelleted feeds) more efficiently than do catfish or trout, but most commercial tilapia feeds are pelletized to reduce nutrient loss. In the absence of feeds specifically prepared for tilapia, a commercial catfish feed with a crude protein content of 28 to 32 percent is appropriate in the United States.

1 comment:

Anonymous said...

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Health Articles

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
Sanford Research/USD
Sioux Falls, SD
(605) 328-1304