Final Report for FS00-120
The production of Tilapia in tanks, within environmentally controlled buildings, has become a well-established, aquaculture enterprise in the Southern Region. There are currently twenty Tilapia producers in Virginia. They all raise the fish indoors in tanks. It is illegal to raise Tilapia outside in ponds or raceways because there is concern about them escaping into the wild. Unlike many cold-water species, Tilapia can live in water that has heavy concentration of nutrients and bacteria. Their ability to withstand poor quality water makes them an ideal food fish for tank culture.
Even though Tilapia can live in poor quality water, the tank water does have to be cleaned constantly. Body wastes from the fish and leftover feed contaminate the water with bacteria, ammonia, phosphorus and other nutrients. Almost all of the producers use a re-circulating system with bio-filters to reduce the bacteria. It is difficult to remove the nutrients from these systems. Many Tilapia growers remove nutrients and enhance the profitability of these operations by adding production of hydroponic vegetables to the Tilapia tank system to remove nitrogen and phosphorus from the water. This kind of production is generally profitable during the off season but is generally not profitable during the summer months. When nutrients build up in Tilapia tank water, during the summer months, the waste water is often just applied to land.
Fresh cut flowers generally have higher value than vegetables during the summer growing season and the producer reasoned that they would be a good way to utilize the effluent from the tanks. He grew fresh cut flowers in a gravel bed using the effluent from his existing Tilapia tanks from May through September. He also grew cut flowers using a commercial nutrient solution. Even though the concentration of nutrients was much higher in the commercial solution, he found no difference in growth or yield between the two systems.
After much experimentation with the timing and amount of effluent application he found he could produce cut flowers with no fungus or wilt problems. The only problems he has left to solve are those of insects. Because the system recirculates the water, he couldn’t spray for insects because the spray would be carried in the recirculating water back to the fish and kill them. Local florists were happy with the quality of his flowers and when he solves the insect control issue, he will have a ready market for his flowers.