Aquaculture industries, and in particular the farming of fish and crustaceans, are major contributors to the economy of many countries and an increasingly important component in global food supply. However, the severe impact of aquatic microbial diseases on production performance remains a challenge to these industries. This article considers the potential applications of microalgal technology in the control of such diseases. At the simplest level, microalgae offer health-promoting benefits as a nutritional supplement in feed meal because of their digestibility and high content of proteins, lipids and essential nutrients. Furthermore, some microalgal species possess natural anti-microbial compounds or contain biomolecules that can serve as immunostimulants. In addition, emerging genetic engineering technologies in microalgae offer the possibility of producing ‘functional feed additives’ in which novel and specific bioactives, such as fish growth hormones, anti-bacterials, subunit vaccines, and virus-targeted interfering RNAs, are components of the algal supplement. The evaluation of such technologies for farm applications is an important step in the future development of sustainable aquaculture.

RNA interference (RNAi) is a powerful tool that can be used to specifically knock-down gene expression using double-stranded RNA (dsRNA) effector molecules. This approach can be used in aquaculture as an investigation instrument and to improve the immune responses against viral pathogens, among other applications. Although this method was first described in shrimp in the mid-2000s, at present, no practical approach has been developed for the use of dsRNA in shrimp farms, as the limiting factor for farm-scale usage in the aquaculture sector is the lack of cost-effective and simple dsRNA synthesis and administration procedures. Despite these limitations, different RNAi-based approaches have been successfully tested at the laboratory level, with a particular focus on shrimp. The use of RNAi technology is particularly attractive for the shrimp industry because crustaceans do not have an adaptive immune system, making traditional vaccination methods unfeasible. This review summarizes recent studies and the state-of-the-art on the mechanism of action, design, use, and administration methods of dsRNA, as applied to shrimp. In addition, potential constraints that may hinder the deployment of RNAi-based methods in the crustacean aquaculture sector are considered.

The review encapsulates the comprehensive exploration of RNA interference technology's application in shrimp aquaculture, covering molecular intricacies, production methods, and practical applications. The emphasis is on exploring the stability and delivery of gene‐specific double‐stranded RNA, particularly through nanoencapsulation. This is because the susceptibility of dsRNA to degradation and limited cellular penetration, emphasising the need for effective delivery mechanisms. The review presents an in‐depth exploration of nanoparticles for the encapsulation and delivery of dsRNA, including virus‐like particles (VLPs), and non‐viral based nanoparticles such as liposomes, chitosan, and beta‐glucan. VLPs, derived from non‐infectious shrimp virus structures, exhibit biocompatibility and natural functionality, making them suitable carriers for dsRNA. The application of chitosan and its derivatives are explored for their efficacy in reducing viral infections in shrimp. Beta‐glucan particles are examined for their immunostimulant properties in shrimp aquaculture. The text emphasises the use of yeast‐based glucan particles for encapsulating dsRNA, showcasing their potential in preventing viral diseases in shrimp. The review introduces cautionary considerations for nanoparticle formulation, highlighting factors such as pH, organic solvents, metal ions, and environmental ribonuclease that can impact dsRNA stability during synthesis. In conclusion, the text discusses the potential economic worthiness and environmental risk assessment of dsRNA technology in shrimp aquaculture. While acknowledging successful applications in other environments, it underscores the need for regulatory approval and risk assessment for dsRNA‐based products in the aquaculture industry. The evaluation of dsRNA in real‐world shrimp farms is deemed necessary for commercial utilisation, taking into account income, expenses, safety, and environmental considerations.

Viral infection of farmed fish and shellfish represents a major issue within the aquaculture industry. One potential control strategy involves RNA interference of viral gene expression through the oral delivery of specific double-stranded RNA (dsRNA). In previous work, we have shown that recombinant dsRNA can be produced in the chloroplast of the edible microalga Chlamydomonas reinhardtii and used to control disease in shrimp. Here, we report a significant improvement in antiviral dsRNA production and its use to protect shrimp against white spot syndrome virus (WSSV). A new strategy for dsRNA synthesis was developed that uses two convergent copies of the endogenous rrnS promoter to drive high-level transcription of both strands of the WSSV gene element in the chloroplast. Quantitative RT-PCR indicated that ~119 ng dsRNA was produced per liter of culture of the transgenic microalga. This represents an ~10-fold increase in dsRNA relative to our previous report. The engineered alga was assessed for its ability to prevent WSSV infection when fed to shrimp larvae prior to a challenge with the virus. The survival of shrimp given feed supplemented with dried alga containing the dsRNA was significantly enhanced (~69% survival) relative to a negative control (<10% survival). The findings suggest that this new dsRNA production platform could be employed as a low-cost, low-tech control method for aquaculture.