Shrimp is the most consumed seafood item in the United States, but its production is still inadequate to meet consumer demand and high-quality domestic supplies are lacking. To facilitate intensive farming of brackish water species, recirculating aquaculture systems (RAS) can be adopted. This allows farmers to control inputs and outputs, helps save water and salt costs, and prevents adverse environmental impact. This project focuses on assessing the effects of two different types of RAS (clear water and hybrid), along with horizontal substrate on intensive Pacific white Shrimp production and water quality. Clearwater (CW) RAS is an effective strategy for shrimp production but may have relatively high equipment and operational costs. Simple hybrid systems (HY) have some advantages as external biofilters maintain water quality, but solids filtration is relatively minimal. Artificial horizontal substrate in RAS may help to enhance shrimp production by increasing the surface area for shrimp to graze and facilitating higher shrimp density, thereby justifying more intensive filtration.
In this study two levels of each experimental factor will be used, and they are system type (CW vs HY) and presence of an artificial substrate (WS) versus absence of substrate (NS). There will be a total of 4 treatments: HY-WS, HY-NS, CW-WS, and CW-NS each of them having four replicates randomly assigned to 1 m3 circular tanks. Ozone, a strong oxidizing agent, will be used in CW tanks. CW will have a foam fractionator, a settling chamber, and a biofilter. HY will have a settling chamber and a biofilter, and suspended solids will be allowed to accumulate in the tank. Four layers of horizontal cloth net, each layer covering 0.5 m2 area, 20 cm apart from each other, and square in shape will be installed as substrate in the eight circular tanks with substrate. Shrimp will be stocked at 400 m-3 in the experimental tanks and reared for 12 weeks.
Results from this experiment are expected to show significant differences in the average weight, total harvest, FCR, and growth rate of shrimp between system types and level of horizontal substrate. We expect shrimp performance to be enhanced by the extra filtration of CW systems and by the added surface area and grazing opportunity provided in the WS treatments. Turbidity, TAN, nitrite, nitrate, TSS, and VSS concentrations are expected to be significantly higher in HY systems compared to CW, which may create disparities in shrimp production as well. Isotope levels (δ 13C and δ 15N) in the tissues of shrimp grown with substrate are expected to indicate that shrimp had access to an additional food source besides commercial feed. Overall, we expect to find a dynamic series of independent and interactive effects of system type and substrate availability. These differences in RAS management may have important implications for intensive shrimp production, especially in locations where low water use, and high product output are critical considerations.