The Evolution of the Bio-floc Technology

Interview with Harvey Persyn: At the Sixth Central American Symposium on Aquaculture (Honduras, August 2001), I chatted with Harvey Persyn, a shrimp farming consultant and major player in the development of shrimp farming in Colombia, Brazil and Venezuela, about some of his youthful experiences with super-intensive, low-exchange shrimp culture systems.  In 1975, while working at Ralston Purina’s shrimp research facility in Crystal River, Florida (on the grounds of the Florida Power Company), Persyn grew shrimp in bacteria-based bioreactors.  He worked out the protein levels in the microbial flocs (35%), fed the bacteria with sugar, used low protein feeds, kept everything in suspension with lots of air, analyzed the cycling of the nutrients from shrimp to bacteria and back again, monitored all the important water quality variables, and produced of 2.7 kg/m² of 18-gram animals.  He said one experimental unit had fifteen layers of substrate spaced 2.5 inches apart that produced around 30 kg/m³.  Dr. Addison Lawrence, currently a Regents Professor at Texas A&M University, consulted on the project, which continued until October 1981, when Purina closed the facility.

Shrimp News: If you knew about the amazing productivity of these systems, why did you build so many big semi-intensive farms in Latin America?

Harvey Persyn: Basically because the world and investors were not ready for shrimp bioreactors.  Investors want a track record.  Farmers want their neighbor to try it first.  At the time, big semi-intensive farms were the way to go, and they remain the state-of-the-art in the Western Hemisphere today.  Belize Aquaculture, the big new super-intensive farm, might change all of that.  It and other projects around the world have inspired lots of confidence in bio-floc shrimp farming.  The world is ready now.

Interview with Steven Serfling: At the World Aquaculture Society (WAS) Meeting in San Diego, California, USA (January 2002), I interviewed Steven Serfling, president of Sunwater Technologies, a consulting company that specializes in recirculating aquaculture systems.  In the late 1970s and early 1980s, Serfling, then running Solar Aquafarms in Encinitas, California, USA, developed a unique bio-floc system for intensive culture of shrimp.

Shrimp News: Hi Steve.  Tell me a little bit about the pioneering work you did with shrimp in closed systems in the late 1970s.

Steven Serfling: During the early years at Solar Aquafarms, from 1974 to 1984, the goal was to develop closed-cycle, controlled-environment, ecology-based systems for culturing fish and shrimp.  Various types of low-cost, solar greenhouse-covered raceways and circular tanks were developed to allow year-round production in cold-winter climates, like the USA.  Many types of aeration and biofiltration were tested to allow the higher production rates required to justify the higher capital investment in the culture system.  We first experimented with the freshwater prawns,Macrobrachium rosenbergii, and tilapia during the mid-1970s.

Shrimp News: What got you started with marine shrimp?

Steven Serfling: At that time no one had been able to raise marine shrimp to normal market sizes or to breed them in recirculating tanks.  Macrobrachium had immediate potential if we could overcome the density/cannibalism problem.  We developed several types of horizontal and vertical habitats and producedMacrobrachium yields equaling 10,000 pounds/acre/year, but that still represented a marginal return on investment.  So we switched to marine shrimp, Penaeus vannamei.  We calculated that if we could achieve yields of 20,000 pounds/acre/year (say three crops at 6,000-7,000 pounds each) and sold the shrimp head-on, the technology would pay for itself.

Shrimp News: What led you to develop your unusual “microbial soup” water treatment method?

Steven Serfling: We started out testing a variety of conventional water treatment methods and equipment, like trickling filters, submerged biofilms, slow-sand and pressure-sand filters, clarifiers, UV and ozone—all designed to remove solids from the water and keep it clear and sterile.  During a visit to several highly productive shrimp estuaries and ponds in Ecuador and Costa Rica, however, it was obvious that shrimp, at least P. vannamei, grew very well in water with high levels of suspended algae and detritus.  So we threw out the filters, clarifiers and sterilizers and duplicated the rich estuary ecosystem in our tanks.  The nickname that stuck for the treatment process was “ODAS,” for “Organic Detrital Algae Soup,” a mixture of hundreds of different species of microalgae, beneficial bacteria, detrital flocs, protozoans and zooplankton that thrive on shrimp wastes.

Shrimp News: Did you plan to have the shrimp feed on the microbial flocs?

Steven Serfling: No, that was an accidental discovery.  I’d heard that vannameigrew well in low-density ponds without commercial feeds, making their living on the natural foods in the pond.  I was curious about how vannamei compared to other species, so we ran feeding trials with monodon, stylirostris and vannamei in aquaria.  We discovered that vannamei would eat all kinds of stuff that the other species would not touch.

Shrimp News: How did you discover that vannamei could filter algae directly from the water?

Steven Serfling: During that period we were also raising Spirulina algae on a research and pilot commercial scale.  We put some live Spirulina in an aquarium with juvenile vannamei and to our surprise the shrimp immediately rose up in the water column and started eating the Spirulina.  Within five minutes they had filtered all the Spirulina out of the water, their stomachs turned green and you could watch the Spirulina pass though their systems.  But Spirulina is too expensive to grow as shrimp feed, so we looked at other alga species.  We learned that regardless of how small the microalgae were, as long as they were attached or trapped in detrital flocs, either suspended or settled, or on biofilms on the sides or bottoms of the tanks, the shrimp would consume the algae, either by picking or filtering.  When feeding, they would either swim after the flocs or simply stand on the bottom and sweep them into their mouths.

Shrimp News: I visited your facility during that period and remember you saying, “the water column is the filter.”  I thought you were crazy.

Steven Serfling: You weren’t the only one who thought we were crazy!  Even though we showed people the “biofilter,” they were convinced we had some elaborate system hidden behind the greenhouses.  We tested vertical and horizontal substrates that were originally designed for a Macrobrachium system, including one that was almost identical to the current “AquaMats” product.  In fact, we even obtained a patent for a water treatment process that uses vertically suspended biofilms as a key component.  But at the densities we targeted at that time with vannamei (7,000 pounds/acre/crop with three crops a year), substrates provided no significant benefit.  They may be helpful at higher densities.

Shrimp News: How did you aerate?

Steven Serfling: With diffused air lifts and sometimes paddlewheels.  One thing we learned early on was that you had to have continuous mixing and aeration to keep solids in suspension.  Otherwise, anaerobic pockets and the resultant hydrogen sulfide would kill the shrimp.  In those days, critics said aeration was too expensive for raising shrimp, but our analysis indicated that aeration only added about $0.06 to a pound of shrimp.

Shrimp News: What salinities were you working with?

Steven Serfling: We tested salinities from 3 to 10 parts per thousand (ppt), and the shrimp appeared to do as well at 3-5 ppt as at 10 ppt.  We knew that vannameicould tolerate low salinities, but at that time we thought it too risky to raise them in freshwater.  It was a closed system, so the cost of salt for 3-5 ppt was very minor.

Interview with John Ogle: At Aquaculture 2004 (Hawaii, USA, March 1–5, 2004), I chatted with John Ogle about the history of super-intensive, bacteria-based shrimp farming.  John is a research associate in fisheries and shrimp aquaculture at the University of Southern Mississippi’s Gulf Coast Research Lab, which has embarked on a program to make inland, indoor shrimp farming profitable in the United States.  John built and will soon begin running trials at the Lab’s new shrimp research facility in Ocean Springs, Mississippi, which got flooded by Hurricane Katrina (August 2005), but most of the facilities survived.

Shrimp News: What was your first experience with microbial flocs in shrimp farming?

John Ogle: In 1989, we were running experiments on all kinds of filtration systems and weren’t particularly happy with any of them.  Out of frustration, in November 1989, we stocked a raceway with Penaeus vannamei that had no filters, just to see what would happen.  We ran an air line down the middle of the raceway, and in about 30 days we had this bacterial floc.  We knew what it was because it’s the same type of floc that appears in sewage treatment lagoons.  What we really discovered was that P. vannamei will live and grow in an aerated, marine sewage lagoon, down to about five parts per thousand salt.  Our raceways actually produced a light floc that we called fluff.

It takes about 30 days for the flocs to develop.  You go through an algae bloom, some foam, and then almost magically, the thing flips to floc.  The shrimp begin feeding on it immediately and you can cut back on the amount of traditional feed that you use.

That was our first experience with floc filters and we have been using them almost continuously ever since.  We designed and built a new building just to take advantage of them.  In fact, we don’t use any other kind of filter.  We even use them in shrimp nurseries.

Shrimp News: In your first trials, how much aeration did you use?

John Ogle: We used a one-inch pipe with holes drilled in it and ran it on a little Sweetwater L-20 Blower.  Oxygen levels stayed high, from 4 to 12 parts per million, averaging around 6 ppm.  At production densities, these systems remain stable for about 12 weeks, but as the shrimp grow larger, oxygen levels drop and growth slows.  We lost a tank that was in production for 22 weeks and contained 25-gram shrimp.  The load was so high that the oxygen dropped and we lost them.

We have some zero-exchange, floc-filter systems that have been running for a year, and the shrimp are still perking along.  The floc is so thick you can almost take it out with a fish net.  What we’re trying to find out now is what levels of floc are ideal for shrimp farming, and then we plan to build a system that takes advantage of those levels.

Taiwan and Thailand: In the late 1980s, hundreds of small-scale shrimp farmers in Taiwan learned that they could produce 10 tons of shrimp per hectare per crop—if they aerated heavily, pumped a lot of water and fed high-quality feeds.  Suddenly Taiwan was producing 100,000 metric tons of farmed shrimp a year.  Then diseases hit, and it took the industry a decade to recover.  In the early 1990s, Thailand appeared to be headed in the same direction, but when the whitespot virus hit, the Thais added some new wrinkles to the Taiwanese technology—reservoirs, settling ponds, filtration, water treatment, waste disposal and zero water exchange—and continued to increase production throughout the 1990s and early 2000s.

Stephen Hopkins: Give Stephen Hopkins (then manager of the Waddell Mariculture Center in Beaufort, SC, USA, now raising tropical fish in Hawaii) credit for publishing the first research on bio-floc shrimp ponds.  In the early 1990s, after a tour of intensive shrimp farms in Taiwan in the 1980s, Hopkins and his colleagues—Paul Sandifer, Al Stokes and Craig Browdy—began conducting research on super-intensive production in bio-floc ponds.  Their results are well documented in the annals of the World Aquaculture Society.

The United States and Latin America: Researchers and consultants in the United States and shrimp hatcheries and farms in Latin America contributed the following:

• Disease-free, genetically improved seedstock, like Penaeus vannamei, which
feed on microbial flocs

• A scientific understanding of zero-exchange ponds

• New feeding strategies that take advantage of the pond ecology

• Pilot and industrial-scale tests of bio-floc shrimp farming

Ken Leber and Gary Pruder and Shaun Moss: In 1988, Leber and Pruder, researchers at the Oceanic Institute in Hawaii, showed that under intensive culture conditions, juvenile shrimp reared in organically rich pond water and fed either a medium or high-quality diet grew significantly faster than juveniles fed identical diets but reared in clear well water.  Growth enhancement likely resulted from the assimilation of suspended organic matter produced in the pond.  Shaun Moss, current shrimp program director at the Oceanic Institute, continues to look at the benefits of the nutrients in pond water.

Russ Allen: In 1994, Russ Allen, a shrimp farming consultant, built a small pilot-scale, bio-floc system in his shop, followed, in 1998, by a $500,000, prototype system in a barn behind his house.  Allen says: Using bio-flocs is a completely different, nontraditional method of managing shrimp ponds.  Instead of managing algal density and oxygen through water exchange, water is never pumped in or out of the pond during a production cycle.  Water quality is managed through fertilization, feeding rates and, in intensive culture, aeration.  Increased production per unit area brings the farmer much higher profits, although at a higher capital investment (aeration equipment, electric installations, fuel costs and seedstock).

Allen also designed and built the first phase of Belize Aquaculture, Ltd.

The Global Aquaculture Advocate (www.gaalliance.org): The Advocate, the bimonthly publication of the Global Aquaculture Alliance, covered the development of bio-floc shrimp farming better than any other aquaculture publication.  Give George Chamberlain, president of GAA, and Robins McIntosh, former general manager at Belize Aquaculture, credit for spreading the word on the scientific aspects of the new technology.

Robins McIntosh: In the August/October 1999 issue of The Advocate McIntosh wrote: The basis of the culture system in ponds is the promotion of a bacteria-dominated, stable ecological system, instead of the phytoplankton-dominated system, which can be highly unstable.  The ponds are fed a combination organic mix and shrimp feed from the start of the cycle, at a rate that is much greater than would be consumed by the shrimp.  The idea is to promote the growth of bacteria and establish a large outdoor bioreactor, or a system similar to a sewage oxidation pond.  The ponds start out with a phytoplankton bloom, but by week 8-10 of culture, these blooms are replaced by microbial flocs.  Ponds can be easily differentiated as to their stage of development.  Young ponds will be green and create large amounts of foam on the surface.  Older ponds will turn brownish/blackish in color and be free of foam on the water surface.  Water from the older ponds is dominated by large organic/microbial flocs that rapidly settle out if water circulation is stopped.  Once the ponds reach this older stage they are highly stable and can assimilate large amounts of organic inputs.  Ammonia levels are generally under 2 ppm, pH generally ranges from 7.0 to 7.5, and dissolved oxygen levels range from 4.0 to 6.0 mg/l.  Feeding levels as high as 450 kg/ha/day have been used.

More McIntosh: In the February 2000 edition of The Advocate, McIntosh said: In a zero-exchange, intensive, culture system, it is important to keep solids in suspension as much as is possible.  At times, the organic loading in our system can reach 500 kg of feeds/hectare/day.  Belize Aquaculture uses paddlewheel aerators to set up a circular flow pattern in square ponds.  Around the outer areas of the pond where water flow rates are greatest, the detritus and other organics are kept in suspension.  As the water flow rates diminish towards the center area of the ponds, larger, heavier particles settle out.  In our ponds, water flow rates of 6.0-12.0 meters per minute are used to keep organic material in suspension.  Towards the middle of the pond the flow rates decrease to less than 6.0 meters per minute and solids begin to fall out of suspension.