###### Abstract  
Designing good recirculating aquaculture systems (RASs) is challenging in shrimp aquaculture. In this study, two sets of RASs were constructed using sea cucumber nursery tanks for rearing _Litopenaeus nunnani_. Recirculating aquaculture was supported by key technologies such as sewage collection and aeration systems adapted to the rectangular tanks and technologies for the removal of sewage, shrimp shells, and dead individuals. Six-hundred and eighty-five thousand juveniles were selected for rearing in the newly constructed RASs, where the average stocking density was 1013 shrimp/m\({}^{3}\). During the recirculating aquaculture period of 53 days, the water temperature of the tanks was 24-31 \({}^{\circ}\)C, the salinity was 25-32%, the pH was 6.4-8.2, the DO was \(\geq\) 4.9 mg/L, the concentration of total ammonia nitrogen (TAN) was maintained between 0.17 and 4.9 mg/L, the concentration of nitrite nitrogen (NO\({}_{2}\)-N) was between 0.12 and 4.7 mg/L, and the total number of _Vibrio_ bacteria remained between 330 and 9700 cfu/mL. At the end of the experiment, the final average weight of individual shrimp was 13.43 g, and the average yield reached 12.92 kg/m\({}^{3}\). The great improvement in growth performance marks a breakthrough in RAS technology of shrimp, and it supports the use of an innovative methodology for the retrofitting and utilization of idle sea cucumber nursery tanks. Litopenaeus vammanei; recirculating aquaculture system; intensive shrimp culture; industrial aquaculture; retrofit +
Footnote †: journal: selected  
Accepted: 8 October 2021  
Footnote †: journal: selected
been proposed. However, using rectangular sea cucumber nursery tanks in the traditional factory-based water flow shrimp culture mode could not meet the requirements under the pressure of national environmental protection policies. Recirculating aquaculture system (RAS) technology represents the most advanced development in aquaculture, and it will define the future of this sector [3]. As such, it was proposed as a solution to the problem of successfully repurposing the sea cucumber tanks: these nursery tanks were retrofitted to RASs for _Litopenaeus nannanei_ farming, ultimately re-establishing a rational use of resources and bringing significant economic benefits. In the 1990s, several experiments were carried out in the United States using recirculating raceway systems to rear _Litopenaeus vannanei_[4]. In the past 30 years, scientists have continuously explored the recirculating aquaculture modes for rearing _Litopenaeus vannanei_. These recirculating aquaculture technologies include raceway RAS [5], high place pond RAS [6], fully enclosed land-based RAS [7; 8; 9], constructed wetland RAS [10], and small RAS experimental facilities [11; 12; 13; 14]. However, few reports on farms containing a water volume exceeding 100 m\({}^{3}\) and an average biomass yield above 6 kg/m\({}^{3}\) have been published so far for this species. Recirculating aquaculture has the advantage of allowing high stocking densities and has been recognized as the way forward in terms of future development of aquaculture technology. However, RAS technology is not yet sufficiently applicable to the large-scale, high-density, and high-yield farming of _Litopenaeus vannanei_. Therefore, for this particular species, RAS aquaculture needs further experimentation and upgrading. The traditional shrimp farming industry in China is restricted by factors such as climate change, shrimp larval quality, and disease outbreaks. Shrimp production largely depends on weather conditions. There is no planning or stability in this type of farming, and it is not possible to achieve stable improvements in shrimp production [1; 2]. At the same time, the discharge of aquaculture wastewater, which does not meet the industrial development requirements in China, causes tremendous pressure on the environment. Therefore, the shrimp farming industry in China has come to a crossroads, and a reform is urgently needed.