Marine shrimp aquaculture has become a worldwide industry with farms mostly located in Asia and Latin America, ranging from Mexico to Peru, and China to Australia. Despite different environments, ecosystems, farming systems and technology, expansion of shrimp farming came with its diseases, which also are today widespread around the globe. Among pathogens involved, bacteria from the Vibrio genus are very common in seawater and different strains from different species are known for causing pathologies like Early Mortality Disease (EMS), currently known as Acute Hepatopancreatic Necrosis Disease (AHPND). As shrimp are fragile animals with no acquired immunity system, alternatives to antibiotic treatments are sought for by the industry, to stimulate natural defences. Among sustainable candidates, plant extracts have shown promising results to limit Vibrio infection in aquaculture. In this context, several experiments were conducted in to evaluate the potential of a plant extract blend (PEB) against Vibrio bacteria.
Firstly, in vitro assays were done using a liquid formulation based on the plant extract blend to evaluate the inhibition effect against several Vibrio strains from different locations worldwide. Secondly, an in vivo trial was performed by infecting shrimp with Vibrio parahaemolyticus. The challenge dose of 1.5 x 105 CFU/mL was selected as the official challenge dose for the main trial after doing a calibration test and calculating with probit analysis. Then, 500 Specific pathogen free (SPF) whiteleg shrimp (Litopeneaus vannamei) with an average initial weight of ~1 g/shrimp were divided into 20 tanks. The set-up was 4 different treatments and 5 replicates for each treatment. The 4 treatments included negative control (no infection), positive control (infection without any product), and two PEB treatments (infection, with PEB in powder included as a preventive product at 0,1% and 0,2% in extruded feeds). Trial duration was 27 days (2 days of acclimation + 14 days of pre-challenge + 1 day of main challenge + 10 days of post-challenge). During the trial, survival rate as well as immunological parameters were measured.
The use of the PEB led to a global inhibition of Vibrio bacteria growth in vitro. At the end of the in vivo trial, improvement of survival rate after infection with Vibrio parahaemolyticus was observed (Fig.1). Other results including immunological parameters like phenoloxidase activity suggest that the PEB was able to stimulate shrimp defences and therefore limit disease consequences after V. parahaemolyticus infection, underlining PEB as a promising solution to vibriosis in shrimp farming.