Authors: Dennis P. DeLong (North Carolina State University), Thomas M. Losordo (North Carolina State University) and James E. Rakocy (Unversity of the Virgin Islands)
The popularity of live tilapia in the marketplace has driven much of the development of the tank-based industry in the United States. In the southern region, indoor tank culture of tilapia allows year-round production and can be a good alternative to pond or cage culture.
Intensive tank culture offers several advantages over the use of ponds. The high density of fish in tanks disrupts breeding behavior and allows male and female tilapia to be grown together. If cultured together, females will be half the size of the males (0.75 lbs vs. 1.5 lbs; 340 grams vs. 680 grams). Females will not reach marketable size at the same time as the males unless there is a market for the smaller fish. In ponds, mixed-sex populations breed so prolifically that parents and offspring compete for food, individual fish growth is reduced, and the population becomes stunted.
Using tanks allows the fish culturist to manage stocks and have a good deal of control over environmental parameters (e.g., water temperature, dissolved oxygen concentration, pH, waste) that can be adjusted to promote maximum production. In addition, feeding and harvesting operations require less time and labor than in ponds. In small tanks it is practical and economical to treat diseases with therapeutants applied to the culture water. Intensive tank culture can produce high yields, year-round, on small parcels of land.
Tank culture also has disadvantages. Because fish have little natural food in tanks, they must be fed a complete diet containing the protein, vitamins and minerals necessary for good growth. Finishing (often referred to as on-growing) feed for tank culture operations generally has more protein than that used for pond culture, usually 32 to 40 percent protein. Pond culture operations, and those tank operations that are heterotrophic or “biofloc” systems, usually can achieve satisfactory growth rates using feed with lower protein content because fish receive a portion of their nutrition from the pond biota or from the ingestion of bacteria. Biofloc systems maintain an active suspension of bacteria and algae in the culture tanks. These bacteria and algae control the ammonia-nitrogen concentration, while the cells are kept in a constant state of rapid growth and regeneration.
In tank culture, the cost of pumping water and aeration or oxygenation increases unit production costs. The filtration technology of recirculating systems can be complex and capital intensive, and these systems require close attention. The high densities required for profitability also create a vulnerability to disaster if power outages or equipment failure occur. Any tank culture system that relies on continuous water pumping, aeration or oxygenation is at risk of mechanical or electrical failure and major fish mortality without the proper backup systems. Automated alarms, oxygen storage, backup generators and quick response can be critical in saving a crop of fish. Confining fish in tanks at high densities can create stressful conditions and increase the risk of disease outbreaks, especially when water quality deteriorates.
Suitability of tilapia for tank culture
Tilapia have a number of characteristics that make them attractive for tank culture. They can tolerate the crowding and handling that is required in a tank-based facility. Their heavy slime coat protects them from abrasion and bacterial infections that would adversely affect many other fish. Tilapia grow well at high densities in the confinement of tanks when good water quality is maintained, but they are also amazingly tolerant of poor or variable water quality. Tilapia can be grown on diets that are high in vegetable matter, such as soy protein, which is a more renewable and sustainable ingredient than fish meal derived from wild fish catches.
The simplicity of breeding tilapia means that fingerlings can be readily available year-round. This characteristic is important to indoor facilities that produce fish steadily for the live market and its customers, which can then rely upon a constant, predictable supply. Fillet yield of most tilapias is 30 to 35 percent of the whole body weight, so 65 to 70 percent of the processed fish is discarded if it is not sold as a live or whole product. Therefore, the more profitable product is the whole/live form.
A number of tilapia species have been cultured in the U.S. With the growth of the tilapia industry and stocks moving from state to state, there has been considerable mixing of strains. Among the reasons for selective breeding, genetic selection, and examination of hybrids has been the improvement of growth rate, cold tolerance and fillet yield, and more desirable color variations for the marketplace. The most popular species currently cultured are the Nile tilapia (Oreochromis aureus). However, other species such as the Mozambique tilapia (Oreochromis mossambicus) and several hybrids are also cultured. While O. niloticus can survive temperatures as low as about 10 ºC (50 ºF), O. aureus can survive to about 7 ºC (45 ºF) but has a slower growth rate. Although these temperatures may be the lethal limits, water temperature in the 10 to 16 ºC (50 to 60 ºF) range can stress tilapia, reduce their feeding behavior, and make them more vulnerable to disease.
Tilapias’ tolerance of lower temperature may make it possible to overwinter stock in some areas of the U.S., but cold tolerance can be viewed as a negative characteristic by state agencies worried about the survival of escaped fish. As with any aquaculture specie, it is prudent for the prospective aquaculturist to consult regulatory agencies early in the planning process.
Continue to Tank Culture of Tilapia (part 2)