The effects of filtration and horizontal substrate on Pacific White Shrimp (Litopenaeus vannamei) production and water quality in RAS

Abstract

To produce high-quality, fresh shrimp near consumer markets in a sustainable fashion, recirculating aquaculture systems (RAS) can be employed. This project assessed the effects of two types of RAS: clear water (CW) and hybrid (HY), along with horizontal substrate, on intensive Pacific White Shrimp production and water quality. In CW RAS a very clean environment is created using a series of filters, but the technique may have relatively high equipment costs. More simplistic HY systems have external biofilters to cycle nutrients, but solids filtration is relatively minimal. Horizontal substrate may help to enhance shrimp production by increasing the surface area for shrimp to graze and escape competition. In this study, two levels of each experimental factor were used: system type (CW vs HY) and systems with substrate (WS) versus those with no substrate (NS). There were four treatments: HY-WS, HY-NS, CW-WS, and CW-NS, each of them with four replicates randomly assigned to 1-m³ circular tanks. Shrimp with an average weight of 1.3 g were stocked at a density of 450 m⁻³ and reared for 53 days. The HY-WS treatment resulted in significantly higher individual shrimp weight, total biomass harvested (7 kg m⁻³), survival, and growth rate compared to the HY-NS and CW-NS treatments. The CW-WS treatment was not significantly different than HY-WS or HY-NS treatments with regard to these parameters. TAN and nitrite-N were significantly lower in HY systems and those systems that contained substrate. The CW-NS treatment had a very high nitrite-N concentration. This resulted in low survival and may have been due to excess ozone entering the biofilters in the CW treatments and killing the nitrifying bacteria. Findings from this study suggest that inclusion of horizontal substrate in hybrid-style systems can significantly enhance production and help in biofiltration, but care should be taken with regard to disinfection measures.