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PROBIOTICS 

FOR AQUACULTURE

Science-based aquaculture has driven the growth of the industry globally.

 

What are Probiotics?

The term probiotic is defined as below by FAO/WHO.   There have been attempts to expand the definition largely by companies that find it easier to market probiotics than bioremediation and the result has been that most users believe that the products work as below.   The accepted definition is:
1. a living microbial formulation: 
Bacteria (or fungi) must be alive when administered.  Dead organisms are not probiotics.
Probiotics work inside the animal.   They do not work on the surface of the animal, in the air, in the water or anywhere in the environment outside of the gut of the animal. 
2. given orally: 
3. colonize the gut: 
They must be able to live in the gut and establish themselves as components of the microbiome.  This can be short or long term.
4. impact the microbiome: 
By colonizing the gut they change the vast assemblages of microbes in the gut in a favorable manner.
5. improve health: 
The final outcome of this is a positive impact on the health of the host.   This could manifest itself in a number of ways, although ultimately the mechanism must be by altering the microbiome.

This is a straightforward definition.  Yet the vast majority of products being sold for use as probiotics fail to meet the definition.

 

Are they really probiotics?    

 

The terms bioremediation and bioaugmentation more accurately describe mechanisms of actions than the term probiotic does.  If they were truly probiotics they would be regulated as claims about impact on animal health typically are.   Unfortunately, the use of the term probiotic has become so convoluted that even vaccines can be called probiotics.   In fact, at this time any organism whether living or dead applied in many manner can be (and often is) termed a probiotic.   This is misleading and confusing as well as a proliferation of pseudoscience at the expense of naïve shrimp and fish farmers.   Very few if any of the bacterial and fungal products sold act in manner that would classify them as true probiotics. 

 

The point here is that without some qualification as to how the word probiotic is being used many users will have expectations that cannot possibly be met.  While I would prefer to avoid the use of the term as it relates to our products, the truth is that I have no control over this.  The term can be used interchangeably for our products although the end user is advised that the mechanism of action of these products (as well as all similar products) is not that of a probiotic as defined above.   

 

Interactions between the shrimp, the environment and pathogens determine the outcome of any disease process.  Many variables come into play and control is often elusive.    Control of as many of these variables as is possible can dramatically increase the potential effectiveness of the use of our products.   Curious about what I mean?  Please ask.

 

A true probiotic functions internally altering the bacterial composition in the digestive tract of the shrimp making it more difficult for pathogens to enter the animal through the gut.  With shrimp, intestinal retention times are too short for the spores to germinate.  Some fish are similar although most are not.   The spores pass through the animals in the feces where they are re-ingested, metabolically active, by the foraging shrimp or fish. 

 

Theoretical additional potential benefits include better digestions of feeds, better growth rates, less disease and less use of antibiotics.  External use of our products in the immediate environment can alter the bacterial flora in the pond short term.  Potential benefits from this are moderation of environmental parameters, including reduction in suspended solid levels, ammonia degradation, and an overall reduction of stress on the animals with the concomitant reduction of specific types of bacterial pathogens in the environment, lessening the impact of bacterial and water quality related health problems. 

 

The evidence that products of this nature function as probiotics (as defined above) in aquaculture is largely anecdotal.  Difficulty in generating scientifically valid data is due to several reasons. One is that the purported composition of many products is for the farmer not for his animals.  Inclusion of certain kinds of microbes, such as Nitrosomonas and Nitrobacter are for sale purposes only.  These are extremely difficult to grow and die off very quickly in products.    The second has to do with the numbers of microbes in these types of products.  Numbers range from some liquid products with less than 10,000 per ml to dry products with more than 4 billion per gram.  Simple mathematical calculations show that with many products it is not possible to add high enough levels of bacteria to affect changes in environments that already have high levels of stable bacterial populations.  A third reason is that the aquatic environment is dynamic and constantly changing naturally and there are many mechanisms in play that act to stabilize the microbiome. 

 

There are many different types of products in the market place.  The products that have the strongest argument (and data) in favor of their effectiveness are those that contain the gram positive bacteria, Bacillus subtilis and its relatives.   These bacteria are ubiquitous, colonize both internal and external surfaces of shrimp and fish and possess a wide range of biochemical abilities that make them ideally suited as candidates to alter the bacterial composition of aquatic environments.  They produce heat stable forms, spores, that allow for long shelf lives and are tolerant of environmental extremes. 

 

Given the addition of the right types of microbes under the right conditions the addition of certain mixtures of microbes to feed and to the environment does have merit and can produce beneficial results.   As a marine microbiologist, my perspective on the current state of the science has evolved over 40 years of experience in the field and the lab. One of my conclusions,  reflected in our approach to this market is:
 

Each pond is different and effective programs need to take this into account