Thursday, March 5, 2015

05/03/2015: Using seaweed 
to prevent Vibrio

by Jean Peignon, aqua technical service, Olmix, Vietnam

First published in International Aquafeed, January-February 2015

With unique expertise in the use of clay and algae, Olmix has developed a new product aimed at the improvement of shrimp performance through increased digestive enzyme activity and better digestive balance vital in preventing Vibrio. The solution lies in improving gut health. 

Shrimp farming started to develop in the 1970s. In 2012, world shrimp production was over 4 million tonnes and more than 50 percent of the shrimp eaten in the world today comes from aquaculture. South East Asia and China represent the largest and the most productive shrimp production areas, accounting for 80 percent of world production.

Although shrimp production has boomed over the last few decades, farmers have to face a variety of issues to ensure their production. Shrimp are very sensitive animals and many disease outbreaks have occurred in the past, such as white spot viral disease in 1994-1995 in south East Asia, and some are still ongoing, such as Early Mortality in Shrimp syndrome, hitting stocks across South East Asia since 2010. 

One of the most important of these diseases is Vibriosis, which kills shrimp at all stages of the production cycle. More than ten Vibrio species have been reported pathogenic for shrimp. Though Vibrio bacteria are part of the natural flora and culture environment of shrimp, Vibriosis can occur in a context of imbalanced environment and may cause total mortality of the reared shrimp. 

During the last two decades, mass mortality incidents in growout ponds and hatcheries due to Vibrio were widely reported. Among the different Vibrio species, Vibrio harveyi is considered one of the most important shrimp pathogens.

With very good management practices, it is possible to limit the Vibrio problem. In order to have complete protection against the pathogen, it is important to find ways to prevent shrimp being contaminated by Vibrio. 

Antibiotics and chemotherapy are often used to manage disease outbreaks. However, these methods have limits, such as environmental hazards or the spread of antibiotic-resistant bacteria. Another way to prevent Vibrio disease is improved gut health. The gut is one of the most important conduits used by Vibrio to infect shrimp. It is possible to favour the natural defences of the gut by preserving its natural balance to avoid Vibrio development and toxicity.

While there is scientific evidence showing the benefits of clays in the prevention or treatment of digestive problems and in the protection of the gut mucosa, much less is known about their capacity to improve feed efficiency. Yet the improvement of the digestibility of feed is an integral property of clays. The mechanisms involved are thought to be multiple (Reichardt, 2008). The dominant hypothesis described in the literature is that clays slow down the transit of feed in the intestine, so the time for digestion is increased, hence a better digestibility of feed and increased nutrient uptake.
 Nevertheless, it seems that the action of clays to enhance feed digestion in the intestine also involves other mechanisms. Reichardt (2008) and Habold et al (2009) both report the ability of clays to favor the contact between enzymes and nutrients and therefore to improve the rate of digestion of the feed. Indeed, digestive enzymes need to be in contact with their substrate in order for hydrolysis to occur. 

The physico-chemical interactions of the enzymes with clay particles seem to enhance the contact between the digestive enzymes and the feed, making clays a good supporting matrix for enzymes and acting as a meeting point for them to be in contact with their substrate. Indeed, Cabezas et al (1991) demonstrated that clay-enzyme complexes are formed at enteric pH values. These active stable complexes are resistant to proteolysis and increase the amount of active digestive enzymes in the intestine, thus improving nutrient digestibility. 

In the same way, Habold et al (2009) observed higher pancreatic lipase activity in rats supplemented with Kaolinite; Xia et al (2004) showed an increase in small intestinal digestive enzyme activity in broilers supplemented with Montmorillonite; and Paolo et al (1999) observed an increase in protein and energy retention coefficients for growing pigs supplemented with clay. Some studies also suggest that the increased activity of enzymes in contact with clay comes not only from their stabilisation, but also from the presence of cofactors in the clay (Reichardt, 2008; Habold et al, 2009). 

Cofactors are defined as thermostable non-protein compounds that form the active portion of an enzyme system. In other words, cofactors are helper molecules required for enzymes to be active. They can be organic or inorganic, most commonly vitamins in the first case and metallic ions in the latter. 

Clays are layered mineral materials, composed of a succession of aluminum and silicium based sheets, the order of which varies depending on the type of clay. 

In Montmorillonite, several metallic ions replace some aluminum and silicium ions in the structure. Known as the substitution phenomenon, this event provides montmorillonite with part of its physico-chemical reactivity. Moreover, the presence of metallic ions may contribute to the activation of some enzymes, through their action of cofactors (Niederhoffer, 2000). In this way, copper is known to activate lipase and phospholipase A (Jondreville et al, 2002) and zinc is a required cofactor of carboxypetidase (Williams, 1960), to mention only a couple of examples. 

The combination of the matrix support provided by the clay and the cofactor effect coming from the metallic ions present in its structure can be referred to as biocatalysis: the improvement of performance of a biochemical reaction through the action of an external compound, a biocatalyst. Due to a large variety of clay minerals, one can imagine that all clays do not have the same potential for biocatalysis depending on their type, their purity, their source or their treatment. As such, clay structure can be modified and associated with other materials in order to unlock its biocatalytic properties. 

Such technology has been developed by Olmix group (France) in the course of its research conducted on seaweeds and clays. The micronized form allows a fine dispersion of the product in the intestine, providing many sites of enzymatic digestive reaction with more easily accessible metal ions. 

Moreover, it benefits from a synergy between clay and seaweeds in the process of biocatalysis, as seaweeds bring in many diverse metallic ions, sometimes absent in the feed, which are required cofactors for the activation of several enzymes. 

This unique combination of seaweeds and clay makes it a unique tool to boost enzyme activity through the action of biocatalysis. MFeed+, the only product benefiting from this new technology, has proven its efficacy in several studies. In one, MFeed+ was tested on shrimp by researchers at Kasetsart University (Thailand). The aim of the study was to evaluate the effect of MFeed+ feed supplementation on digestive and growth performance of Penaeus vannamei.

375 shrimp (6.3±0.2g weight) were distributed in fifteen 500 L glass tanks containing 25 shrimp each. After a 7-day period of acclimatization during which all shrimp were fed the basal diet, tanks were randomly allotted to one of three treatments (5 replicates per treatment): one control, fed the basal diet and two MFeed+ groups, for which the basal diet was supplemented with 0.1 percent or 0.2 percent MFeed+. Growth performance parameters and mortality were recorded during the 60 days of supplementation. 

Vibrio bacteria were counted in the hepatopancreas and the intestine at 60 days as a marker of digestive health. The shrimp were fed three times a day to satisfaction. The feed amount was adjusted daily based on the feeding ability of the shrimp. Uneaten feed was siphoned out of the tank 2 hours after feeding. Water used in the experiment was seawater, with salinity adjusted to 12-15 ppt. The water in the tanks was aerated with air stone and exchanged every 2-3 days at the rate of 10-30 percent volume depending on its visible quality.

Feed Conversion Ratio was greatly improved in groups receiving MFeed+. As a consequence, average final weight and specific growth rate of shrimp supplemented with MFeed+ tended to be higher. Moreover, better digestive performance helped to improve the digestive status of the shrimp, as demonstrated by a lower Vibrio count in the hepatopancreas and the intestine and the improved survival rate of the juveniles. This study highlighted the potential of MFeed+ to improve digestive and zootechnical performance of shrimp.

Read the magazine HERE.

The Aquaculturists
This blog is maintained by The Aquaculturists staff and is supported by the
magazine International Aquafeed which is published by
Perendale Publishers Ltd

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