A new solution to handle vibrio challenges in shrimps
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by Mathieu Calmont, Area Business Manager EMEA (Europe – Middle East – Africa), France, and Kristin Sandersen Gretland, Technical Sales Manager, Borregaard, Scandinavia, Norway
n many countries, shrimp aquaculture production is depressed by disease, particularly caused by vibrio bacteria. Antibiotics, which have been used in large quantities, are in many cases ineffective, or result in increased virulence of pathogens. Formaldehyde products have been widely used, and resistance behavior has started to appear in shrimp farming. Vibrio parahaemolyticus and Vibrio harveyi have been described as the main pathogens in shrimp species. These pathogens cause serious infections and decreased productivity both in hatcheries and ponds. In addition, this leads to reduced feed conversion and reduced growth rate in surviving individuals. Most bacterial aquatic diseases are related to vibrio bacteria. These bacteria usually dominate the normal microflora of farmed and wild penaeoidean shrimp. Bacteria will colonise in the digestive tract, release toxins, and eventually destroy the digestive organ known as hepatopancreas. This is leading to high mortality - up to 90 percent. A new product, SoftAcid Aqua Deca, has been developed and optimised to be used in all phases of shrimp production (from algae to growing phase). The product inhibits growth and biofilm formation of vibrio, not allowing vibrio species to colonise the digestive tracts of the shrimp. Shrimp feeding studies have shown positive results – with higher survival rate, increase in biomass and reduction in feed conversion cost.
Figure 1: Pyrogallol unit
Introduction to the work done
The goals for this project were to develop a unique product that can be used in several stages of the shrimp production, in addition to having a positive impact on reduction of biofilm- and bacteria formation. The work started with laboratory trials where the bactericidal effect towards different vibrio strains was studied. As a second step, the bacteriostatic effect was studied with respect to quorum sensing and biofilm formation. Quorum sensing (QS) is a mechanism by which bacteria coordinate the expression of certain genes in response to the presence or absence of small signal molecules. It appears that several of the virulence factors of Vibrio harveyi are regulated by QS and extracellular toxin production is known to be one of the biggest causes of vibrio toxicity. Cultivated shrimp can be protected from vibriosis by disruption of quorum sensing. Earlier findings have stated that pyrogallol units disrupts QS in Vibrio [1-2]. The lignosulphonic acid present in SoftAcid Aqua Deca has a polyphenolic structure, similar to the pyrogallol unit seen in other polyphenols. (See Figures 1 and 2). Earlier experiences have shown positive effects towards biofilm removal when using SoftAcid. In the shrimp industry, it is believed that vibrio bacteria stick to the digestive tract of the shrimp by creating a biofilm. Laboratory trials with biofilm adhesion were performed in order to see the effect of SoftAcid
Figure 2: Molecular structure of Lignosulphonic acid
28 | April 2020 - International Aquafeed