Development of a zero water discharge (ZWD)—Recirculating aquaculture system (RAS) hybrid system for super intensive white shrimp (Litopenaeus vannamei) culture under low salinity conditions and its industrial trial in commercial shrimp urban farming in Gresik, East Java, Indonesia

Abstract

This study aims to develop a hybrid zero water discharge (ZWD) - recirculating aquaculture system (RAS) system to improve water quality, as well as the growth, survival, and productivity, of the super-intensive white shrimp culture under low salinity conditions at semi-mass and the industrial level. The study consisted of two parts: (1) a semi-mass trial for the optimization of shrimp production using a hybrid ZWD-RAS system with a total volume of 2.7 m3 at the different shrimp stocking densities of 500 PL/m3, 750 PL/m3, and 1,000 PL/m3 and (2) an industrial trial at a commercial shrimp urban farming facility in Gresik, East Java, with total volume of 110 m3 at the optimum shrimp stocking density from the semi-mass trial. Both the semi-mass and industrial trials were performed in five steps: (1) preparation and installation of the RAS and ZWD system components; (2) preparation of microbial components including nitrifying bacteria, the microalgae Chaetoceros muelleri, and the probiotic heterotrophic bacteria Bacillus megaterium; (3) acclimatization of white shrimp post larvae from the salinity level of 32 ppt to 5 ppt; (4) conditioning of the biofilter used in the RAS and shrimp tank (microbial loop manipulation in ZWD); and (5) shrimp grow-out rearing for 84 days and 60 days for the semi-mass trial and the industrial trial, respectively. The hybrid system combined a ZWD system and an RAS. Shrimp tanks were conditioned with the addition of microbial components for ZWD at the beginning of the culture period. The RAS was operated when NH4+ and NO2−-N levels in shrimp culture reached above 1 ppm until the levels decreased to 0–0.5 ppm. The culture performance in the semi-mass trial at 500 PL/m3, 750 PL/m3, and 1,000 PL/m3 stocking densities was not significantly different for final mean body weight (12.06 ± 5.72, 11.84 ± 3.58, 12.04 ± 3.71 g/ind, respectively) and productivity (4.205 ± 0.071, 4.691 ± 0.025, 4.816 ± 0.129 kg/m3, respectively). Significant differences in survival (70 ± 7%, 53 ± 3%, 40 ± 4%, respectively) and feed conversion ratios (1.54 ± 0.01, 1.82 ± 0.00, 2.16 ± 0.03, respectively) were observed between the three different stocking densities. Water quality parameters and microbial loads during the semi-mass trial were similar for all stocking densities and were within the tolerance levels for white shrimp grow-out production. The results of the semi-mass trial showed that the hybrid ZWD-RAS system can maintain water quality and a microbial load up to a 1,000 PL/m3 stocking density; however, the optimum performance based on survival, feed conversion ratio, and productivity was reached at the 500 PL/m3 stocking density. The industrial trial of the application of the hybrid ZWD-RAS system using the optimal stocking density of 500 PL/m3 resulted in a comparable shrimp survival of 78% with a total production of 298 kg shrimp biomass (equal to a productivity level of 2.7 kg/m3). The overall results of both the semi-mass and industrial trials showed that the application of a hybrid ZWD-RAS system allows optimal shrimp survival and growth at the stocking density of 500 PL/m3 and has high potential for application in commercial shrimp grow-out production at low salinity levels.