The Use of Probiotics in Aquaculture (Read!)

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May 9, 2007
Northwest Canada
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The use of probiotics in aquaculture has been around for decades but has gained some new popularity in the past few years due to a few fish food manufacturers incorporating some of these bacteria in their food.

While numerous publications & studies about the use of probiotics and/or prebiotics in aquaculture have emerged during the last decade, we still know very little about their use regarding the vast amount of ornamental species of fish found in this hobby.

Here's what we do know.

There are numerous strains of probiotic bacteria, each targeting different types of aquatic pathogens. In order for any of these probiotics to be fully effective, they must be in a live form, or able to be reactivated once in the GI tract of the host. One can also simply add these bacteria to the tank water on a regular basis.

Probiotics have been applied as dietary additives or water additives to improve growth performance and immune response, to improve water quality (by increased waste reduction), and to outcompete pathogenic bacteria.

Bacillus species such as B. subtilis and B. licheniformis are commonly used as probiotics in aquaculture, but there are numerous other bacteria species that are also being utilized within the aquatic industry. In order for probiotics to have any type of positive effect on the fish, they must survive in very large quantity.

Probiotics are usually defined as live microbial feed supplements which beneficially affect the host animal by improving its intestinal microbial balance (Fuller, 1989). Based on this definition, probiotics may include microbial adjuncts that prevent pathogens from proliferating in the intestinal tract (Gatesoupe, 1994). Most probiotics proposed as biological control agents in aquaculture belong to the lactic acid bacteria(LAB). But LAB has some limitations due to having a small antibacterial spectrum. These activities normally inhibit only closely related species of gram-positive microorganisms (Suma et al., 1998). However, almost all the pathogens involved in aquaculture are gram-negative bacteria. Bacillus subtilis, a gram-positive, aerobic, endospore-forming bacterium, would fall under this category, yet this is exactly what two of the fish food manufacturers using probiotics have listed in their ingredients as their only source of probiotic bacteria. The reason for that seems to be that spores of Bacillus strains are thermo-stabile which makes them much easier to use in heat processed pellets.

This is certainly not a new concept in aquaculture, these same type of heterotrophic bacteria have been manufactured for use in septic systems for decades, and there are a number of aquatic related companies that have been marketing these same types of enzymes & micro organisms for just as long.

A couple of fish food manufacturers have stated that their probiotic is based on Bacillus subtilis spores, a good commercial example of that being Calsporin, manufactured by the Calpis Co. Ltd out of Tokyo Japan.

Does it work? Well, according to the more positive studies, yes & no.

While it does improve the overall feed conversion ratio (FCR) the food used in that study mostly consisted of soybeans & wheat, and while it did have a positive affect on the intestinal microbiota at the initial stages of the feed trial, that apparently soon diminished over time. The longer it was fed, the lesser the positive affect. Also, while it was shown to elevate the expression of some immune related genes, it did not improve the disease resistance of koi challenged with Aeromonas hydrophila, which is one of the most problematic species of Aeromonas found in commercial aquaculture.

So what does that tell the average hobbyist that keeps ornamental species of fish?

Not a whole lot.

If you feed your fish a diet that is high in terrestrial based carbs such as gluten meal, corn, soybeans, wheat, potatoes, rice, etc - adding a probiotic such as Bacillus subtilis in large enough quantity could possibly increase the feed conversion ratio (depending on the species of fish), thereby causing an increase in growth, as well as a reduction in overall waste compared to feeding the same quality of feed, sans the probiotic. It could also help elevate the immune system of the fish, but so could numerous bioactive compounds found in natural raw ingredients such as, Antarctic Krill, Garlic, Spirulina, and micro algae such as Haematococcus pluvialis. Not to mention utilizing key vitamins & trace minerals at levels that far exceed the industry standards. As an example, instead of having a post extrusion level of 140 mg/kg of Vitamin C, having a level of 500+ mg/kg of Vitamin C. (with most of that coming from the raw ingredients themselves) Certainly some of these bacteria have been shown in some studies and using certain species of fish that they can improve the overall feed conversion ratio ....... but of foods that mostly consist of wheat & soybeans.

Of course that's a non issue for anyone that is NOT feeding large amounts of terrestrial based starch derived from corn, wheat, soybeans, potatos, etc to their fish.

Some of this is just plain old common sense, but some consumers can easily be sucked in by the hype.

Feed low cost crappy ingredients but add *special* bacteria to digest crappy ingredients, and charge twice the price of higher quality feeds that contain higher quality raw ingredients ....... simply because the former contain bacteria spores? Unfortunately many people buy into this type of hype or fad marketing.

The truth is you can have both, without breaking the bank on bacteria that comes from the dirt, and is dirt cheap if you know where to look (not at your LFS). More on that later.

Beyond just increasing the feed conversion ratio, and promoting growth, probiotics are also very effective at reducing waste. From an organic reduction standpoint, this isn't exactly cutting edge technology. These exact same heterotrophic bacteria have been used to digest & remove waste from septic systems for decades, the only difference being that in the past no one referred to them as probiotics. And as many of these septic system companies saw the potential for added revenue, they started marketing and selling these non-pathogenic *probiotic* bacteria for ponds, and aquariums. The truth is some are just as safe, and work just as well, as many of the aquatic based products that sell for 10-20 times the price. Some are the exact same bacteria being used, with a different label.

There's another plus side to dosing with these types of bacteria (non pathogenic) beyond just consuming organics, or increasing feed conversion ratios - it's called competitive exclusion.

Competitive exclusion is a term used in aquariums to keep pathogenic (bad) bacteria in low levels in an aquarium or pond.

By adding known harmless waste eating bacteria in large numbers the added bacteria out competes any existing bad bacteria for the nutrients in the tank and therefore is a safe and effective way to starve off infectious bacteria. In the medical industry this technique is called 'bacterial interference' and is used to displace pathogens by using harmless bacteria.

This is a successful way for beginners to keep your fish healthy. In a new tank there will be virtually no bacteria to out-compete bad bacteria that may be in the fish's gut. So with micro-particles of fish food floating down to the substrate, the bacteria from the fish, ornaments and of course the aquarists hands are all a huge food source for bacteria and are able to grow with no competition from anything else.

By adding harmless bacteria from a commercial bottle in large quantities, you starve off the bad bacteria by sheer volume.

This method also reduces maintenance on your filter and helps keep the gravel cleaner as the bacteria consumes all decaying material and breaks down dead plant matter that would otherwise take weeks to breakdown. This method is commonly used in human sewage treatment to break down human produced mulm. This method is why having a soil-based (Walstad) tank is so successful. The soil has tens of thousands of species, with billions upon billions of bacteria in it which keeps pathogenic bacteria levels very low.

Probiotics: The New Ecofriendly Alternative Measures of Disease Control for Sustainable Aquaculture

Now factor in what has taken place in the aquatic trade over the past 10-15 years, starting around the time that internet trade became very popular among hobbyists. Not only are we seeing a lot more fish from areas where super intensive farm practices are in use, but also where these same commercial farms are known for their use of antibiotics, steroids, hormones, and a plethora of other drugs that would never be allowed in fish destined for human consumption. (in America)

The problem is that some of these bacteria are known to evolve very quickly, and many strains have over time become resistant to traditional drugs. It is for this reason that commercial aquaculture circles are now seeking alternative routes to treating fish pathogens via more natural methods, but the reality is they are now only doing so due to their own large scale & long term abuse of medications such as antibiotics.

Today every man & his dog has become an importer of fish, and just like the person that just flew in from SE Asia carrying a new strain of influenza, some of these imported farm fish are carrying their own viral & bacterial mutations when they arrive here.

Still not concerned about antibiotic resistant pathogenic bacteria finding their way into your aquariums? Read this:

Imported ornamental fish are colonized with antibiotic-resistant bacteria.

Rose S, Hill R, Bermudez LE, Miller-Morgan T.
Source Department of Biomedical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, OR, USA; Department of Microbiology, College of Science, Oregon State University, Corvallis, OR, USA.


There has been growing concern about the overuse of antibiotics in the ornamental fish industry and its possible effect on the increasing drug resistance in both commensal and pathogenic organisms in these fish. The aim of this study was to carry out an assessment of the diversity of bacteria, including pathogens, in ornamental fish species imported into North America and to assess their antibiotic resistance. Kidney samples were collected from 32 freshwater ornamental fish of various species, which arrived to an importing facility in Portland, Oregon from Colombia, Singapore and Florida. Sixty-four unique bacterial colonies were isolated and identified by PCR using bacterial 16S primers and DNA sequencing. Multiple isolates were identified as bacteria with potential to cause disease in both fish and humans. The antibiotic resistance profile of each isolate was performed for nine different antibiotics. Among them, cefotaxime (16% resistance among isolates) was the antibiotic associated with more activity, while the least active was tetracycline (77% resistant). Knowing information about the diversity of bacteria in imported ornamental fish, as well as the resistance profiles for the bacteria will be useful in more effectively treating clinical infected fish, and also potential zoonoses in the future.

© 2013 Blackwell Publishing Ltd.

and this ..........

Fancy fish could harbor dangerous bacteria
by Rose Eveleth February 6, 2013 03:00am PST

Around the world, private collectors and businesses maintain beautiful fish tanks stocked with colorful corals, speedy little cichlids and stately angelfish. But a hidden danger lurks: many fish that wind up in aquariums carry antibiotic-resistant bacteria that could pose a threat not just to a billion-dollar industry but to human health.

A recent study published in the Journal of Fish Diseases measured 32 different ornamental fish that entered the port in Portland, Ore., from places such as Colombia, Singapore and Florida. The specimens were found to carry 64 different bacterial colonies, and many were resistant to antibiotics to varying degrees. The bottom line: not only were the fish more susceptible to infection, but their bacteria harbored genes that could make them immune to drugs - genes they can pass along.

Resistance to antibiotics can develop in a number of ways, but the most common culprit is overtreatment, a practice commonly used when fish are transported.

The chain of events is pretty easy to follow. The majority of ornamental fish start their lives in Asia and other exotic locations and are shipped all across the globe. Those trips aren’t a walk in the park for the animals, says Luiz Bermudez, a microbiologist at Oregon State University, and one of the researchers on the study.

“It’s stressful even if we humans get in an airplane and fly for 14 hours,” he says, “so when a fish gets to a destination, many times the fish presents with a kind of stress-related disease.”

To prevent stocks from going belly-up before they reach their destination, many importers often proactively treat their catch with antibiotics. That, says Bermudez, is a big driver of the antibiotic resistance his team found in the study.

How antibiotic resistance spreads

It’s not just fish who might be in trouble, either. That’s because a resistant bacterial strain can pass its resistance to another species, Bermudez says.

So, in theory, an antibiotic-resistant fish bacteria could transfer the set of genes that confer that resistance to a bacteria that infects humans, Bermudez says. That means a human bacteria that was formerly felled by certain antibiotics would suddenly become immune to them.

Complicating matters is the fact that many antibiotics used to fight fish bacteria are the same ones widely used on humans. Among the antibiotics that the fish bacteria were best at warding off is Tetracycline, a drug used to treat everything from acne to rosacea to cholera in humans. Up to 77 percent of the studied specimens were resistant to this drug.

While it is unlikely that these bacteria will be transmitted from fish to humans, both fish owners and importers should be extra careful. “If you’re going to clean a fish tank, you should be aware that there is a possibility that you’re going to get some infection,” he says.

Aside from the health implications, antibiotic resistance could be a drain on the bottom line for aquarium suppliers. The global market for ornamental fish is worth an estimated $15 billion each year. The world spends $900 million a year alone on just the live fish - a figure that has grown an average of 14 percent each year for the past 25 years. Should certain fish become entirely resistant to the antibiotics that help them survive, the industry could suffer a huge economic blow totaling millions of dollars.

Bermudez says the ornamental fish industry isn’t deaf to the dangers of antibiotic resistance. It has already made some changes based on his team’s research - such as treating fish less frequently with antibiotics unless necessary and figuring out how to ship them more safely.

But the industry deals with 6,000-plus species of fish, shipping from more than 100 countries, and most countries have no specific regulations regarding antibiotic use. So while individual suppliers might do their part to cut back on antibiotics, many are likely to continue preemptively treating their stocks to avoid disease.

There are still some open questions for researchers studying this antibiotic resistance. For example, Bermudez wants to understand whether or not the bacterial community of imported fish changes after a few weeks at a facility in the United States. Perhaps, he says, importers could eliminate fish with these resistant strains before they are transported to fish tanks across the country, preventing the resistance from spreading

For fish and humans alike, the vicious cycle of antibiotic resistance should be a serious concern. That’s because the fewer antibiotics that work to fight a particular disease, the more likely it is to have a negative impact on the population. The more resistant genes that exist, the more likely other bacteria are to become resistant. The longer suppliers rely on antibiotics to broadly safeguard stocks, the more likely they are to develop resistance.

“So now we’re facing a kind of a crisis situation in the case of humans and animals, that many times we don’t have antibiotics or we only have one antibiotic that can be used to kill the microorganisms that’s causing the infection, and that’s a serious problem,” Bermudez says.

Scary stuff ...........

I first used a commercial septic tank bacteria approx 10 yrs ago (to kick start some new set ups) and was impressed with the results. After some recent changes in my personal life I found myself looking for ways to reduce water changes, and filter cleaning, beyond just keeping less fish in each tank, or simply adding pothos to reduce nitrates. I wanted to reduce as much time as possible performing regular maintenance, and I believe that I've found the solution.

While this is all very non scientific, here are my results thus far:

1. Water clarity improved immediately. My water has always been clear, but this bacteria took it to a whole new level. It became crystal clear.

2. It has removed all odours from the water. Not that my water stunk prior to this, but one of my tanks that has 3 plecos, and a lot of driftwood, would start to smell within a week of a water change. I could also always smell a hint of garlic in all of my tanks, but not since introducing this bacteria. Overall both the look & smell of my tanks has improved at least somewhat.

3. The overall organics in my filters has been reduced by at least 50%, probably closer to 60% but let's say 50% to be on the safe side. API states 62% reduction in their tests with their Stress Zyme product, and that's probably a very close number to what mine played out to be in my tanks. My 90 gallon is always munged up with debris/waste from my driftwood eating plecos, and after 3-4 weeks the sludge in those filters is as thick as mud. (and stinky!) After 3+ weeks since my last filter cleaning on this tank the one filter barely required cleaning, the other was easily 50% less dirty than normal - and what was left did not smell nearly as bad as it usually does after 3-4 weeks. Filters that previously could only go 3-4 weeks max, can now easily go 6 weeks or more between cleanings.

4. A tank that I have been fighting a cyanobacteria outbreak for a number of months now no longer has any signs of cyanobacteria slime/algae. A different species of algae (in a very small quantity) has managed to now displace it.

With the septic tank bacteria that I use (SeptoBac) I mix 4 teaspoons (1/2 oz) of the dry powder into a liter or so of tank water, stir occasionally for a couple of hours, then pour the solution divided between 3 tanks: two 125 gallons, and one 90 gallon. Most of the solids are left at the bottom of the main container, and not added to my tanks. What does make it in clears off over night. Some of my fish (especially my clown loaches) will eat some of the solids with no ill effect. For Canadian members this product can be found at your local Walmart.

So far total cost is $4.50 that covers a total of 340 gallons x 16 treatments, which works out to a little over $1 a month.

So far this has been a complete success, and that's not even factoring in the competitive exclusion angle with the non pathogenic probiotic bacteria, out-competing any potential pathogenic bacteria. Increasing feed conversion never factored into this experiment as I don't feed foods that are high in low quality raw ingredients, such as excessive amounts of terrestrial based plant matter. (corn, soybeans, potatos, wheat, etc)

Ultimately the goal is to reduce my water changes from 50% weekly, to 50% by-weekly, while at the same time reducing my filter maintenance to half of what it was prior to the start of this experiment.

Species involved in this experiment; Clown Loaches, Snakeheads, Midas, Severum, German Rams, various Corydora, several BN plecos, and an L14 pleco.

I discussed my initial results with some fellow MFK'ers, Miguel, Tom (Aquanero) and Jeff (aclockworkorange) and a few local fishkeepers, and they also began trials in their tanks, with their fish, using their own mix of septic tank bacteria. I look forward to each of these gents adding their own personal results in their systems with their various species of fish to this discussion.

Please Note - If anyone tries this in their tanks, please make certain that the products are 100% organic, biodegradable, and non-toxic, and do NOT contain any types of surfactants, perfumes, etc.

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