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Answers and Questions on Bioflocs
Ramon Macaraig (email@example.com): Shrimp Guys, we are learning more and more about biofloc technology in open ponds. The shrimp in two of our ponds, one 675 square meters and the other 1,500 square meters, have shrimp that are 18 grams and 20 grams, respectively. They were stocked at 200 and 160 postlarvae per square meter. Estimating from feed consumption calculators, the ponds still have 100 animals and 80 animals per square meter, respectively. About 500 and 600 kilograms were partially harvested from each pond when they were at 12 and 14 grams. Our survival rates are improving, but growth is still slow.
Since a lab reported that our type of toxic Vibrio proliferate at salinities of 0-20 PPT, we stock in full strength seawater to avoid Vibrio problems. The dreaded whitespot is not a factor, though we believe it still lurks in the background. The shrimp seem to be happy, but are still pale orange when cooked. Floc density is being maintained at 10-15 cc per liter, with the TAN (total ammonia nitrogen) at 0.003 levels and alkalinity at 150 PPM. Applications of molasses and beneficial bacteria neutralize TAN. With no ammonia spikes in the system, DO (dissolved oxygen) is maintained at 4.0-5.0 PPM around the clock. Transparency is at 10cm or less. pH is stable at 7.4-7.8.
With survivals getting better, we now want to improve our growth rates. At 120 days of growout, our animals have reached 20 grams with an estimated feed conversion ratio (FCR) at a modest 1.5-1.6.
We had our dried floc analyzed. Proximate analysis showed: protein,12.07%; fat, 2.22%; moisture, 3.06%; ash, 13.8%; fiber, 12.43%; and starch, 13.6%. So floc does not seem to be a good source of shrimp nutrition, but it does stabilize TAN levels. What formulated feed should we use to optimize growth? Would higher protein help?
We should make some money on these two trials because the target harvest weight of 30-grams seems to be achievable at 150 days of culture. By then, we hope to do more than 20 metric tons per hectare. Another question is: How do we optimize power consumption? We’re using around 50 horsepower per hectare on paddlewheels, blowers and submersible Venturi aerators, which keep the floc suspended. Please suggest some ideas that would help us lower our power costs.
We seeded three additional ponds in the last 28 days. The biggest of them is 6,000 square meters, stocked at 150 postlarvae per square meter.
We are feeding rotifers to our postlarvae for the first 30 days. We are also evaluating the feed formulations for each stage of the shrimp’s life cycle.
I thank The Listers for their comments, and I use some of them in the management of our biofloc ponds! I will report the results of the harvests.
By the way, since the floc density stabilizes and even thins out, we are now minimizing the application of molasses and bacteria in the new biofloc ponds, as suggested by Eric, when they reach a floc density of 15 cc.
Mauricio Emerenciano (firstname.lastname@example.org): Ramon, thanks for sharing your information. It’s very interesting.
What’s your nighttime temperature? Nighttime temperatures ranging between 25-27°C might reduce feed digestibility on the order of 20-30%, which would increase your FCR. Another important factor is the characteristics of the feed (composition, digestibility and formulation). As you know, there’s a world of differences among feed brands. Shrimp farmers should run feeding trials and nutritional analyses.
Regarding the floc’s nutritional characteristics, I don’t have much experience with open ponds, but we have seen big differences quickly develop in adjacent ponds. Many factors can contribute to these differences (such as carbon source, shrimp stocking density, light incidence and salinity). In indoor floc culture, we found crude protein content varying from 11 to 35% and lipid varying from 0.5 to 10%. But, independent of the nutritional content, we believe (at least at the moment) that floc should be considered as nutritional supplement rather than a main source of nutrients.
Ramon Macaraig (email@example.com): Mauricio, thanks for the reply. From your nutrition analysis of biofloc information, it looks like the floc is more nutritious than we thought. We may have sampled the floc after it had already been recycled through the shrimp. The fact that vannamei prefer to stay up in the water column, rather than on the bottom, puts them closer to the nutritious biofloc.
It appears that we have to increase the feed volume a bit to achieve better daily growth rates. Since we are still on a feed tray monitoring system, we are looking at a 10% increase in the ration compared to the present 5% increase that we have used since the monodon era when the stocking rates were at 15-25 PLs a square meter.
We consider the nutrition the shrimp get from the floc as a secondary benefit. The primary benefit from the floc is its ability to quickly remove nitrogen from the water. We do not see spikes in ammonia levels with the TAN steady at 0.01-PPM levels. The DO is stable at 4.0-5.0 PPM range, even in the early morning. It is the alkalinity that has to be maintained at 150 ppm, as Billy suggested, and the floc density at 10-15 ml/liter.
Now, we are looking at how to get faster growth. I will keep the list posted on new developments and knowledge derived from the data.
Billy Setio (firstname.lastname@example.org): Ramon, try thinning out your floc a little bit, to 7-10 ml. It will increase the shrimps’ appetite. If you want better growth—feed more! Here’s the concept: Let the floc absorb the nitrogen, and use feed to increase the growth rate. In my experience, you increase the growth rate with more fishmeal. It’s also important to keep a balance ecosystem with floc and algae. A balanced ecosystem encourages growth.
Ramon Macaraig (email@example.com): Billy, thank you for the comments. We have come to the same conclusion: The nutrition from the floc is secondary to the stable environment that it provides, especially with regard to nitrogen levels.
Speaking of the floc, it recently got out of control every week for five weeks, going from 10 ml to 20, 30, 40 and 50 ml, as we continued to apply the same 150kg/ha of molasses. With 20-20 hindsight, we did not catch it immediately, but since our feeding rate was rather low, the floc formation may have come from ammonia seeping up from the pond bottom. We drained off some of the floc into new ponds. The floc density is at 5 ml this week. We will be more vigilant in monitoring the floc density and the alkalinity.
Yet, even after two partial harvests totaling of 8.9 metric tons per hectare from the 1,560 square meter pond, the feed rate data still seem to point to a total survival rate of 83%.
In the 670 square meter pond, we still estimate 115 animals per square meter are in the pond after an 8.2 metric ton partial harvest, from a stocking rate of 200 PLs/sqm. Their color was pale. We will soon pull another partial harvest because the biomass is almost 20 metric tons per hectare now.
We intend to do two more harvests, hopefully at 25 and 30 grams. Prices are moving up!
Billy, thanks for the insights. We are doing three more biofloc ponds. The biggest is 6,000 square meters. About 30 days into the growout cycle, they received biofloc thinned out of the two older ponds.
If the total Ammonia-N is 0.2 PPM, we add 100 kilograms of molasses per hectare. With more data available from our new ponds, we are using less molasses. TAN readings are below 0.1 PPM now. Less molasses should cause less floc and encourage the animals to focus their hunger on formula feeds. It also may require less aeration power.
We have had done some work on algae. Now we allow the algae to gobble up as much of the free ammonia from the feed residues early in the morning and apply the molasses for floc formation around noontime when the DO is above 10 PPM as a result of the morning algae bloom. At this stage, we are having difficulty maintaining a diatom bloom and employ the stable Nannochloropsis green algae to scrub the early morning ammonia ahead of the floc development from whatever TAN is available at noon. It is the blue-green-algae that we are guarding against. They pounce upon ponds with high transparencies and cause digestive problems in juvenile shrimp. Blue-green-algae blooms can, however, easily be corrected by applying urea.
We have to use full strength seawater, like almost every shrimp farm in the General Santos area of Mindanao Island, because the lab analysis of our noxious Vibrio species showed that it likes lower salinities.
In our new cultures, by using less carbon supplements, we hope for moderate floc levels and more feed consumption before 70 days of growout.
With the survival issue stable (fingers crossed), we can focus on feed management; then we’re going to look at our power costs.
Nelson Gerundo (firstname.lastname@example.org): Hi Mauricio and Billy, another important aspect of why Ramon is getting good results is the ideal geographical location of his farm along the unspoiled, beautiful coast of Sarangani Bay in Mindanao, Philippines, far south of the country’s typhoon belt. It’s a perfect site for shrimp farming at the most southern edge of the Philippines that has been supplying not only high-quality seedstock, but also the best fish and shrimp to the country’s seafood markets for a long time.
Ramon Macaraig (email@example.com): Billy, the TAN readings in the intensive non-biofloc ponds were at 0.5ppm as they reached higher biomasses. At 0.2 PPM, we would only need to apply 40 kg of molasses, instead of a 100 kg. Now that they are below 0.1ppm at day-135 in the early morning, even with 15 mt/ha of biomass, we may not need molasses.
When the floc reaches 10ml/cc at day-70, our pond transparency also drops to 10 cm and below. The contribution of the algae is debatable at this point. The algae seem to be very important in keeping the transparency and in scrubbing the TAN early in the culture.
Linda Thornton (firstname.lastname@example.org): Ramon, in your post on March 17, 2017, you said since a lab reported that your type of toxic Vibrio proliferates at salinities of 0-20 PPT, we stock in full strength seawater to avoid Vibrio mortalities.
Can you share more details regarding this statement?
Are you speaking of the toxic form of Vibrio parahaemolyticus?
How many colony-forming units (CFUs) did you find?
Ramon Macaraig (email@example.com): Linda, that was the data we got from the laboratory last November (2016) on Vibrio species collected in the pond water and grown on TCBS agar. It is Vibrio parahaemolyticus. We don’t know if it’s the EMS Vp. We fear whitespot and blame our mortalities on it, but whenever we test dead shrimp for whitespot, they are negative.
Luiz Faria (firstname.lastname@example.org): Hi everyone. I used to work for Farallon Aquaculture. Once you stop using carbohydrates and probiotics to feed the flocs, Vibrio counts drop drastically. At the hatchery level, we learned that keeping the counts below 100,000 CFUs is a must. But after 50,000 CFUs, it’s time to take some action, like increasing algae and water exchange (to reduce nutrients) or treating with antibiotics.
Sources: 1. The Shrimp List (a mailing list for shrimp farmers). Subjects: Biofloc Questions and Question for Ramon Macaraig. March 17 to 30, 2017. 2. Bob Rosenberry, Shrimp News International, April 6, 2017.
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