At the World Aquaculture Society Meeting in Las Vegas, Nevada, USA (February 15, 2006), a special, all-day session brought people from around the world together to discuss bio-floc shrimp farming. They formed a working group within WAS to facilitate communications among interested parties, gave the technology its name—“bio-floc” aquaculture—and established a home for the group at the Agricultural Engineering Society’s website (http://www.aesweb.org/starter.htm, click on Bio-Floc Workgroup in the left hand column).
Dr. Greg Boardman, professor of civil and environmental engineering at Virginia Tech University in Blacksburg, Virginia, USA, and Dr. Yoram Avnimelech (below) chaired the session.
The fourteen presentations varied in length from 20 to 40 minutes. The papers will be published by the Agricultural Engineering Society. Dr. George Chamberlain, a former president of WAS and current president of the Global Aquaculture Alliance, moderated the discussions after the morning and afternoon sessions.
Dr. Yoram Avnimelech: Dr. Avnimelech has taken the lead in the bio-floc aquaculture movement. He is head of the Sea of Galilee Water Shed Research Unit, Chief Scientist of the Israeli Ministry of the Environment, and Dean of the Department of Agricultural Engineering at Technion (the Israel Institute of Technology), where he holds the Samuel Gorney Chair. He has done consulting work in Israel, the United States, South America, Australia and Thailand and has been a visiting professor in various countries, including Belgium, the United States, Australia and the Netherlands. He has published more than a hundred papers in refereed journals, edited four books and trained many graduate students.
Morning Session
Lytha Conquest (Aquatic Feeds and Nutrition Department at the Oceanic Institute in Hawaii, USA).
What’s in floc? Another world: phytoplankton, fungi, silicates, amoeba and nematodes (which disappear quickly because the shrimp selectively pick them out and because they are much larger and easier to grab). Also flocs trap a lot of debris, like fecal material, dead plankton and feed particles. In fact, much of the feed that goes into the pond is not eaten by the shrimp. Instead, it becomes a fertilizer that stimulates a natural food chain that culminates in the flocs. Within the world of the floc, there are a lot of dissolved organics, like simple sugars.
One of the studies that we’re doing right now at the Oceanic Institute is harvesting the floc and extracting various aqueous solid components and incorporating them into shrimp feeds. In April 2006, we plan to start trials with those feeds in clear water systems to see if we get enhanced growth from the floc.
Dr. David Brune (Carter Newman Endowed Chair of Natural Resources Engineering and professor of agriculture and biological engineering at Clemson University, South Carolina, USA).
At Clemson University we have been working with suspended culture microbial systems for twenty years. Currently, we use a partitioned aquaculture system, which has modules for water treatment, tilapia and shrimp. In 2005, we gave tilapia 33% of the system. Algae in these systems assimilate the ammonium, the tilapia harvest the algae, and the water goes back to the shrimp.
In 2005, we added a small, activated sludge reactor to concentrate the sludge as much as possible. We can aerate the sludge at one milligram a liter of oxygen, and then aerate the shrimp at three or four milligrams a liter of oxygen. There is no point in wasting all that energy to aerate the sludge at three or four milligrams per liter, when it only requires one. The idea is to get the respiratory demand of the sludge out of the shrimp module. The sludge reactor was amazingly successful. We were able to concentrate 1,000 milligrams per liter of bacterial solids into a small cylinder.
In 2005 and 2006, we have not removed a single thing from the system. We’re producing 35,000 pounds of shrimp per acre—and we have not removed a thing from the system. No water, no sludge, nothing. There was no nitrate accumulation in the water column. There was no nitrogen in the system. Basically, the nitrogen just degassed.
Dr. Craig Browdy (Senior Marine Scientist at the Waddell Mariculture Center in South Carolina, USA):
The goal of our research is to develop shrimp farming systems that can be applied commercially in the United States. We’re doing a lot of research on replacing sea salts with artificial salts. We use a nursery phase. We feed with trays and use high-protein Zeigler feeds.
As we increased stocking densities, we started using oxygen injection instead of traditional aeration. Now we only use oxygen injectors, and we use heat exchangers in the winter. We capture all our sludge, dewater it, and we’re working on treating it to reduce its volume. We reuse all our water. The water we’re using now is producing its third crop. We’ve kicked production up to 6.7 to 6.8 kilos per square meter. In one trial, we stocked four-gram juveniles and in 59 days produced 16.5-gram shrimp, with a growth rate of about 1.47 grams per week and survival rate of 84%.
Once you have a stable microbial community in the system, it’s very important to reuse the water because you don’t have to go through an algal crash to get the system started again.
The shrimp love the floc; they turn upside down and eat it off the surface.
In our current trials, we’re doing some filtration to reduce the density of the flocs. Trials by others have indicated that when you crop the floc, growth and survival of the animals increases. We crop the floc to avoid shading out the algae, which produce all those nice sugars that vannamei like. In fact, I think those sugars might be the elusive pond water growth factor.
Discussion After the Morning Session
Dr. Rod McNeil: We need to look at more species. I’ve done some work with P. esculentus in Australia and it’s a real vacuum cleaner when it comes to flocs. Its relative nitrogen assimilation efficiency compared to P. vannamei is about 15% higher, so why are we stuck on vannamei?
Steven Serfling: We found that the algae add a key nutritional supplement to the system. People didn’t know this twenty or thirty years ago, but now it’s pretty well known that plant pigments, not just beta-carotene but a whole bunch of carotenoids, and other phytochemicals have incredible nutrition qualities, not just for tilapia and shrimp, but for the zooplankton in the system. They are filter feeding that algae all the time. The shrimp consume them in the flocs and get their “greens” that way.
I would like to say something about the disease prevention benefits of using these systems. In 28 years of using these systems with fish, we’ve never had a disease problem with any species of fish. A massive jungle of microorganisms surrounds and protects the fish. We never restricted anyone from putting their hands in the tanks. You can add sugar or other sources of carbon to these systems and in a few hours your ammonia will drop. To get a drop like that in an algae-based system can take thirty to sixty days, or longer, depending on water temperatures.
Afternoon Session
Dr. Nyan Taw (formerly with PT Central Pertiwi Bahari, a huge shrimp farm in Sumatra, Indonesia, that has commercialized bio-floc technology on part of its farm):
Robins McIntosh (who now works for the Charoen Pokphand Foods, which owns PT Central Pertiwi Bahari) came to our farm three years ago, and with his advice, we started our super-intensive project.
We aerate with Taiwanese paddlewheels at 20 to 28 horsepower per hectare, depending on stocking density. The higher the stocking rate, the lower the survival.
If the sludge and floc get too high we siphon some sludge out or add or drain water.
The 26 ponds in our first commercial trials averaged 22 metric tons of shrimp per hectare per crop of 16 to 18 gram shrimp, with feed conversion ratios of 1.1 to 1.2. In our regular ponds, the FCR was 1.5 to 1.6. Production costs are 15% to 20% lower with floc systems because the of low FCR.
Dr. Shaun Moss (program director for the United States Marine Shrimp Farming Program, the Oceanic Institute, Hawaii, USA):
Our best production so far, 8.9 kilos per square meter!
Christine Beardsley, from the Scripps Institution of Oceanography in San Diego visited us at the Oceanic Institute and identified the protein content of shrimp feces. When a shrimp defecates, the protein content in its fecal strand is only about 15% that of a high-protein feed pellet. After twelve hours, however, it rises to 40% and after a day it goes up to 80%. So there’s protein enrichment of the fecal strand over time. Where’s the protein coming from? If we look at the increase in the bacterial abundance in the feces over time, we see an incredibly high incubation rate. These fecal strands are very important substrates for bacterial colonization, which subsequently can be consumed by the shrimp. We talk about using nitrogen over and over again; well here’s a mechanism for doing that because the bacteria are soaking up the organic and inorganic nitrogen from the water and converting it into protein. The bacterial species that develop on the fecal strand are different from the species associated with the flocs in the water column.
Michael Mogollon (former vice president of production at OceanBoy Farms, an inland, low-salinity, organic, bio-floc shrimp farm in Florida, USA):
What I’m going to talk about today is the system of bacteria/algae management we use at our farm.
We draw water from the Florida aquifer, 1,000 feet down. It has just enough salinity for shrimp and it’s fairly adequate in all the necessary iconic content. High hardness, good alkalinity, a good balance of ions. And very importantly, for our organic certification, it’s free of pesticides and contaminants.
We do a lot of sophisticated plumbing and water movement and have a full lab where we do our own water quality testing. We use bio-flocs in maturation and in the hatchery; we don’t discharge any of that water. In the hatchery, we don’t change any water from day one until day seventeen, from zoea to a PL-10.
The growth of our broodstock is excellent. They usually put on 2.1 grams per week.
In the larval rearing tanks, we use filters to remove some of the solids from the water.
In our nursery ponds, where the animals spend thirty days before being stocked in the growout ponds, we have a feed conversion of 1:1. We stock between 5,000 and 8,000 animals per cubic meter. Survival rates are very good, 90% plus.
In our growout ponds, we use about 25-HP of paddlewheel aeration per hectare. Average stocking density is 110 per square meter. Growout lasts 115 days. Survivals are 65% and improving. We go for a 41/50 count whole shrimp. The growth rate is typically a little over 0.9 grams per week. We get about ten tons per hectare with a feed conversion of 2.0. Our feed conversion is not that good. We remove a lot of solids so that we don’t have to face nitrite spikes. Nitrite is very lethal at our low salinities. We do molasses additions. The system is very stable. Major catastrophes are very, very rare, now.
Dr. Rod McNeil (a shrimp farming consultant who has implemented several bio-floc shrimp farms around the world):
I’ve been working with OceanBoy and a number of other bio-floc shrimp farms. I also visit shrimp farms all over the world and do a lot of data collection, looking at the difference in microbial performance from one farm to the next.
If we look at the nutritional value of flocs produced in the dark and the light, the fatty acid content is much lower in flocs produced in the dark, but the protein content is much higher. Calcium, magnesium and silica are heavily concentrated in the flocs.
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