North Central Regional Aquaculture Center

In cooperation with USDA

Feeding Tilapia in Intensive Recirculating Systems

by Marty Riche1 (United States Department of Agriculture, Agricultural Research Service, Fort Pierce, FL) and Donald Garling2 (Michigan State University, East Lansing, MI)

Benefits of Culturing There are two types of systems used profitable it is important to increase Tilapia in Recirculating for tank culture; flow-through efficiency through feeding manage- Systems systems, and recirculating systems. ment. Flow-through systems are only There are many species of tilapia, practical if geothermal water or Feed Requirements of but only a few are widely cultured waste heat are available. Indoor Tilapia in Recirculating around the world. In the United recirculating systems offer the Systems States the most commonly cultured advantages of reduced land require- species of tilapia are the Nile ments, less water use, and environ- Most wild tilapia are omnivorous, (nilotica), Blue (aurea), Mozambique mental control for year-round meaning they will eat a variety of (mossambicus), Hornorum growth. Recirculating systems can things, including both plants and (hornorum), and hybrids such as the recycle as much as 99 percent of the animals. This is in contrast to many Taiwanese and Florida red. Choos- culture water daily, although 90 other fish that are more specialized. ing a species to culture depends percent recirculation is the preferred However, like other animals, tilapia largely on customer preference, target. To make these systems cost have specific requirements for legal status, growth rate and cold effective the fish are generally reared nutrients such as amino acids from tolerance. intensively. Intensive recirculating protein, fats, minerals and vitamins. tank culture can produce high yields Tilapia are well suited for culturing on small plots of land with little Fish reared in intensive recirculating in ponds, cages, tanks, or raceways. water use. However, recirculating systems have different nutritional Using ponds is the most popular systems tend to be energy intensive requirements than those in the wild. method in the southern United and require high capital invest- Wild tilapia graze on blue-green States due to longer growing ments. Therefore, to make them algae and bacteria. This type of seasons. In the southern most parts feeding requires a lot of energy due of Texas and in Florida water to finding and digesting this type of temperatures can remain warm food. To meet the energy required enough for year-round growth. In for feeding and growth, they must the cooler, temperate regions of the consume more food relative to farm North and Midwest, tank culture is raised fish. In intensive tank culture favored. Tank culture has the added natural food is limited. Therefore, all benefit of reducing time and labor nutrients must be supplied in a required for harvesting and feeding. North Central Regional complete pelleted diet. An advan- Indoor tank culture is the preferred Aquaculture Center tage to feeding a pelleted diet is the method when sufficient warm water Fact Sheet Series #114 higher quality and consistency of the is not available due to climatic USDA grant # 00-38500-8984 diet. conditions. August 2003 Table 1. Suggested standard pellet sizes used for culturists to observe feeding re- feeding tilapia from hatching to market size. sponses. Additionally, the process- Size of fish (grams) Standard Feed Size ing method used in making floating 0–3 # 00, or # 0 pellets increases the amount of 3–10 # 1 energy available to tilapia. 10–25 # 2 25–40 # 3 3 Recommended protein levels for 40–100 ⁄32” tilapia diets range from 32 to 36 1 larger than 100 ⁄8” percent in fingerling feed, and 28 to 32 percent in feed for fish larger than Requirements for each nutrient are result in more expensive production. 40 grams. The amount of energy dependent on a number of factors. Uneaten feed also reduces water provided from fat is generally Some of these factors are biological quality, fish health, and perfor- restricted to 4 to 8 percent of the diet. such as the size, age, condition, and mance. This is especially true in The higher fat content is fed to small reproductive state of the fish. recirculating systems that use low fish and is gradually decreased with Environmental factors such as water exchange. increasing size. temperature, dissolved oxygen, water quality, and photoperiod also Types and size of feeds Feed selection and storage is impor- affect requirements. Feeding man- Newly hatched fry are given a tant when feeding fish in an inten- agement including the amount, and complete diet of powdered feed. The sive recirculating system. A high frequency of feeding, are also feed should be high in protein quality feed with few fine dust-like factors. Finally, the diet itself, (about 50 percent) and energy to particles should be used to reduce including the amount and quality of meet the demands of the fast grow- waste production and minimize the protein, energy, and the method of ing fry. Feed size is gradually load on the biofiltration and oxygen processing will affect the require- increased in relation to growth. A systems. Feed should be kept in a ments. good rule to follow is, “small fish, dry, cool place to ensure maximum small feed; large fish, large feed”. quality and avoid mold formation. How to Feed Tilapia in However, tilapia prefer smaller size Recirculating Systems feed than other commonly cultured Feed rates species, such as salmon, trout or Feeding rates will vary with fish size The optimum feeding method catfish. and water temperature. The appro- depends on the physiology of the priate amount is measured as a species, and economics of the The size should be increased percent of the average body weight. production unit. Historically through various sizes of crumbles As the fish weight increases, the culturists have emphasized maxi- for fingerlings 5 to 40 grams (Table percent body weight fed decreases mizing intake in the hopes of 1). Fish larger than 40 grams should (Table 2). The daily feed ration must maximizing growth. Evidence be fed pellets. The most common be adjusted to compensate for 3 1 suggests this may not be the most pellet sizes for tilapia are ⁄32 inch– ⁄8 growth. effective for fish production. Maxi- inch. Floating pellets are the pre- mizing intake can lead to uneaten ferred type because they allow Fry grow rapidly and will gain close feed, lower feed efficiency, and to 50 percent in body weight every 3 days. The feed rations should be Table 2. Example of daily feeding allowances for different adjusted accordingly. Daily feed sizes of tilapias at 28°C (82°F). Source: National rations should be adjusted weekly Research Council. 1993. Nutrient Requirements of between the range of 5–30 grams, Fish. National Academy Press, Washington, D.C. and once every two weeks beyond Size of fish (grams) Amount of daily feed (% of fish weight) 30 grams. 0–1 30–10 1–5 10–6 Because of their rapid growth, high 5–20 6–4 energy requirements, and small 20–100 4–3 stomachs, fry require frequent larger than 100 3–1.5 feeding. Fry should be fed as many

2 feedings is 4–5 hours, depending on the energy and composition of the diet.

Increased feeding frequen- cies decrease aggressive Figure 1. Stomach and intestine of behavior in some fish tilapia. White arrows show species. This results in faster path of feed when fish are growth and less size varia- fed before the stomach tion. However, there is a as 8-10 empties. Grey arrows show limit to the frequency that times a day. path of feed when fish are will result in benefits. There Because fed at proper intervals. are many fish species that frequent are less efficient when fed at feedings can short intervals. Evidence suggests be labor In some fish species, the first food tilapia fed too frequently utilize intensive, an entering the stomach is the first food feed less efficiently. alternative is to feed fry continu- to leave. However, food eaten by ously throughout the day with tilapia can move past the stomach Water quality concerns automatic feeders. Automatic and enter directly into the intestine Fish are sensitive to water quality. feeders should be checked fre- (Figure 1). Fish fed at 2–3 hour Feeding should be reduced or quently and adjusted if necessary to intervals eat more feed than their stopped if water quality falls below avoid over feeding which can foul stomachs can hold (Figure 2). The certain levels. Shortly after feeding, water quality. extra feed eaten passes over the dissolved oxygen levels decline stomach and is considered wasted. rapidly. Dissolved oxygen levels Fingerlings also grow fast and The result is an increased cost of should be maintained above 5.0 should be fed at least four times a production and lower profits. Fish ppm for best growth. At dissolved day. Fish should be fed less when fed at 4–5 hour intervals eat nearly oxygen levels between 3.0–5.0 ppm water temperature decreases. the same amount of feed needed to feeding should be reduced, and refill their stomachs. This suggests feeding should be stopped at Feeding Frequency the optimal interval between dissolved oxygen levels below 3.0 The interval between feedings may ppm. be more important than the total number of feedings. Feeding strate- gies for tilapia have traditionally been to feed a little bit of feed at frequent intervals. This strategy comes from early work on wild tilapia that eat algae. However, the higher quality and consistency of pelleted diets eliminate the need for many frequent feedings.

The optimal interval between feedings will depend on the return of appetite. Fish eat available food depending on stomach fullness, and at intervals determined by the time it takes to empty the stomach. The Figure 2. Amount of food eaten at different time intervals between speed the stomach empties depends meals. The stomach capacity is the amount of room in the on temperature, fish weight, meal stomach before eating again. The shaded area is the amount size, feed composition, and feeding of food eaten that by-passes the stomach because of lack of frequency. room. 3 Ammonia and nitrite are a concern sion, therefore culturists often refer Conclusion + in intensive recirculating systems to (NH3 + NH4 ) as the total ammonia and should be monitored regularly. nitrogen (given as mg/L-TAN). Tilapia are well suited for aquacul- Ammonia production is directly When measuring or discussing ture. Tilapia grow rapidly and are related to feeding and depends on ammonia concentrations it is impor- fairly resistant to stress and disease. the quality of feed, feeding rate, fish tant to be clear which term is being However, due to climatic conditions, size, and temperature. Following used. the culture of tilapia in most of the feeding activity ammonia levels United States requires the use of begin to rise. In most species of fish, The lethal ammonia concentration intensive recirculating systems and ammonia production peaks 4–6 for most warmwater fish is between formulated diets. Recirculating

hours following feedings. 0.6–2.0 mg/L NH3-N (1 mg/L = 1 systems can be expensive to build ppm). Tilapia begin to die when and operate therefore it is important In water, ammonia exists in two unionized ammonia concentrations to maximize production efficiency.

forms, ammonia (NH3, or unionized are higher than 2.0 mg/L NH3-N. + ammonia) and ammonium (NH4 , or However, unionized ammonia To maximize production efficiency ionized ammonia). The form that is concentrations as low as 1.0 mg/L and minimize costs, tilapia should

most toxic to fish is NH3. Both forms NH3-N will decrease growth and be fed: are present at all times in the water, performance in tilapia. but the percentage of each depends • Nutritionally complete diets on temperature and pH of the Generally smaller fish are more formulated to meet their dietary system. Warmer water and higher sensitive to the toxic effects of requirements; pH in the system favors the more ammonia. Low dissolved oxygen • Optimum crumble or pellet size; • Optimum feeding rate (% of fish toxic NH3. also increases the toxicity of ammo- nia and lowers the concentration that body weight); Unfortunately the term ammonia is affects fish. When ammonia concen- • Optimum time intervals (4 – 5 hours depending on the energy often used to refer to both the toxic trations remain elevated, or fish and composition of the diet); NH (given as mg/L NH -N) and the show signs of stress, feeding should 3 3 based on the size of the fish and two forms(NH +NH +) added be reduced or stopped. 3 4 the culture conditions. together. This often leads to confu-

Additional Reading Many extension articles on tilapia and their culture can be downloaded from the AquaNIC web site: http:// aquanic.org—Check out Tilapia and Recycle under the Beginner drop down menus for Species and Systems, respectively.

1 United States Department of Agriculture, Agricultural Research Service, Harbor Branch Oceanographic Institution, Fort Pierce, FL 2 Department of Fisheries and Wildlife, Michigan State University, East Lansing, MI

Series Editor: Joseph E. Morris, Associate Director, North Central Regional Aquaculture Center. Originally published by Iowa State University, Ames, Iowa Any opinions, findings, conclusions, or recommendations ex- pressed in this publication are those of the author(s), and do not necessarily reflect the views of the United States Department of Agriculture. 4