Greenwater Tank Culture of Tilapia with the Effluent Used as a Source of Water and Nutrients for Terrestrial Crops

Greenwater Tank Culture of Tilapia with the Effluent Used as a Source of Water and Nutrients for Terrestrial Crops

Summary

The United States Virgin Islands imports more than 80% of the seafood and more than 90% of the fruits and vegetables consumed in the territory. Greenwater tank culture of tilapia is an aquaculture technology developed at the University of the Virgin Islands (UVI), which can economically produce fish in a way that is environmentally sustainable. The byproduct of greenwater culture is a concentrated slurry comprised of uneaten feed, feces, dead plankton and bacterial cells. This sludge has been found to be an excellent source of water and nutrients for a variety of crops. Currently, there are no commercial-scale aquaculture operations in the territory. The reason for this is the reluctance of the investors to try a new technology. The systems developed have lacked a technology transfer component. Commercial-scale demonstration systems, supported by government funding but operated by farmers, will serve as educational tools. If local farmers produce the fish themselves and use the resulting effluent as a nutrient and water source for their crops, confidence in the technology will increase and more people will involve themselves in this form of sustainable food production.

Objectives
The goal of this project is to raise the standard of living of Virgin Islanders by introducing them to an environmentally sound, sustainable and economically feasible method of agriculture which will offset a portion of the territory’s seafood and produce deficits. Three objectives must be met to enable this to occur:

1.) Discover if greenwater tank culture production characteristics revealed in experimental units will be duplicated on a commercial scale.
2.) Determine the quality, quantity and value of terrestrial crops produced with greenwater sludge as a water and nutrient source.
3.) Ascertain the economic viability and environmental sustainability of this integrated production technology.

Approach
Three 200-m3 greenwater tanks will be constructed. One tank each on St. John and St. Croix constructed on local farms and managed by local farmers. The third tank will be constructed on the grounds of the UVI Agricultural Experiment Station (AES) and managed by experiment station staff. Participating farmers will take the greenwater sludge derived from the culture tank and incorporate it into their normal irrigation regimes, without adding any additional fertilizers. We will help them design and construct irrigation systems that will meet their particular needs. Fish and vegetable production will be monitored and evaluated.

After the first production cycle, products will be sold, data will be compiled and whole-farm budgets will be developed for the farmers to determine financial viability of the systems. Two extension publications will be written, “Greenwater Tank Culture of Tilapia” and “Utilizing Greenwater Effluent as a Source of Water and Fertilization”. During the second and third years, on-site training sessions will be given to prospective and current farmers at both locations. The training sessions will include greenwater culture techniques, irrigation and fertilization strategies, marketing of the products, and financing and budgeting. Upon completion of the project, the Southern Regional Aquaculture Center (SRAC) will be approached to gauge their interest in supporting a series of publications detailing greenwater culture. From previous experimental greenwater trials at UVI-AES we expect this project to accomplish the aforementioned goals.