In the last years, disease has consistently ranked as a top priority for shrimp producers across the world and has been a bottleneck for future growth. Shrimp pathogens come in many shapes and sizes and can be bacterial in nature (e.g. Vibrio spp.), viral (e.g. IMNV), or parasitic (e.g. EHP). Each pathogen is unique and therefore a different approach is needed to combat each one. This said, Vibrio spp. is a continuous problem and is capable of causing large mortalities directly (e.g. AHPND/ EMS), whilst also being implicated in other pathologies (e.g. WFD).
It is extremely difficult to estimate the true cost of disease, nevertheless, some researchers have tried to do so in major shrimp-producing countries (Figure 1). The actual figure is almost certainly higher, as there are many hidden costs, for example:
In an ideal world, one would like to grow shrimp in the absence of Vibrio and ensure a clean environment. However, this is almost impossible as they have many survival advantages which allow it to proliferate in the shrimp and pond environment.
Figure 1: Estimated economic losses due to shrimp disease in key producing countries. SOURCE: Shinn et al. 2018
Figure 2: Microbiome of healthy and diseased shrimp intestine, hepatopancreas and pond sediment from Mexican shrimp farms. Vibrio abundance in each environment is shown as a percentage. Green boxes represent ‘healthy’ animals whilst red boxes represent ‘diseased’. Microbiome of wild shrimp is indicated by ‘wt’. SOURCE: Cornejo-Granadas et al. 20217
Vibrio is ubiquitous in nature, meaning it forms part of the commensal microbiota in seawater and shrimp environments. In some cases, they can even be the most dominant bacterial species even in healthy ponds and animals (Figure 2). This means, eliminating is almost impossible, so the shrimp must be able to maintain health status and performance, in the presence of Vibrio.
Vibrio spp. are r-strategists which means they have very fast growth rates, especially in non-competitive environments and they typically dominate in unstable water conditions. This is in comparison to most probiotics which are K-strategists, which grow slower but are able to maintain populations close to the carrying capacity and dominate in stable conditions. Interestingly, aquaculture practices (e.g. disinfection, antibiotic usage, feeding management) favors r-strategists. For example, certain Vibrio species have a doubling time of <10 minutes compared to lactic acid bacteria which may take approx. 40 minutes, and Bacillus >50 (Table 1).
| Species | Temperature (°C) | Generation time (mins) | Reference |
| Vibrio parahaemolyticus | 37 | 11-13 | Ulitzur 1974 |
| Vibrio alginolyticus | 37 | 20-25 | Ulitzur 1974 |
| Vibrio natriegens | 37 | < 10 | Eagon 1961 |
| Bacillus | 37 | 53+ | BIOMIN® |
| Pediococcus | 37 | 40 | BIOMIN® |
| Lactobacillus | 37 | 50 | BIOMIN® |
| Enterococcus | 37 | 58 | BIOMIN® |
In a recent paper, researchers took 56 samples from aquaculture ponds in which Vibrio was isolated in each. For each strain, antimicrobial resistance was characterized against 20 commercial antibiotics. Shockingly, nearly 100% of isolates were resistant to commonly used antibiotics in aquaculture, and 68% had multi-drug resistance.
Amongst many other microorganisms, Vibrio can form biofilms - a syntrophic group of cells that stick to each other and often also to a surface. In shrimp ponds, there is ample space and substrate to grow, for example, on pond liners, automatic feeders, aerators, and floating flora and fauna. Biofilms start to form when a small number of bacterial cells communicate (through quorum sensing), recruiting more cells and forming an external matrix (Figure 3). Vibrio can then be shed from the biofilm where they become flagellated and highly virulent. This gives Vibrio a strong advantage since the biofilm offers greater protection against antimicrobial products (e.g. disinfectants and antibiotics).
Figure 3: Biofilm formation of microorganisms, including Vibrio. SOURCE Verderosa et al. 2019
In 2012, the Thai shrimp industry was decimated by an unknown disease, which subsequently spread to other countries. After extensive exploration, the agent was identified as a V. parahaemolyticus that contained a plasmid with genes encoding for insect-related (Pir) toxins, PirA and PirB. These toxins cause extensive damage to the hepatopancreas and can result in rapid mortality, especially in the first 30 days of culture hence its original name ‘early mortality syndrome’, now correctly termed AHPND. It has subsequently been demonstrated that these genes can be horizontally transferred to other Vibrio species, for example V. campbelli, V. harveyi, V. owensii and V. pumensis (Figure 4).
Figure 4: AHPND causing V. parahaemolyticus possessing PirAB plasmid along with non-causing V. parahaemolyticus, devoid of the plasmid. Schematic diagram on the right, demonstrating horizontal gene transfer of plasmid between Vibrio cells.
For the reasons above, a preventative management approach to Vibrio control is far more advantageous than a reactive one. dsm-firmenich has developed a range of feed and water solutions that can target Vibrio and keep their abundance under control, allowing the shrimp not just to survive, but to thrive. These products have synergistic modes of action for greater pathogen control and ultimately bring about greater survival during disease challenges.
For example, modes of action in dsm-firmenich solutions include but are not limited to:
Supported by extensive in vitro, in vivo, and commercial trials, Biotronic® and AquaStar® are complementary in that they can be used together, or individually, at the feed mill, shrimp hatchery and farm.
The Biotronic® line of state-of-the-art enhanced acidifiers support modern farm animals against Gram-negative bacteria.
AquaStar® comprises the most complete range of aquaculture probiotics for hatchery, feed mill and farms to improve growth and enhance pond and water quality.
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