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Molasses, Salinities, Bio-Flocs and Semi-Intensive Ponds
A Discussion from The Shrimp List
For background information on this discussion see:
Indo-Gulf Shrimps (firstname.lastname@example.org): Most probiotic bacteria prefer normal oceanic salinities of around 35 parts per thousand, or less. For example, in many parts of India, Vibrio outbreaks occur during the hotter months when the salinities and temperatures are above annual averages. Therefore, is it advisable to manipulate the carbon:nitrogen ratio in a shrimp pond by adding an organic carbon compound like molasses when salinities rise above 45 ppt?
Will higher salinities, higher temperatures and all that molasses (or other carbohydrate) encourage the growth of organisms that might be harmful to the shrimp, like Vibrios?
Eric De Muylder (email@example.com): I have no idea whether the increased carbon would favor "good" bacteria more than the "bad" Vibrios, or not, although I would assume so. But the problem is going to be that the increased carbon is going to increase the oxygen demand of the pond. Now you have to aerate more, increasing your evaporation rate, the last thing you want to do when you already have high salinity.
Laurence (firstname.lastname@example.org): I don’t see any reason why heterotrophic bacteria promoted by molasses addition should not be similarly effective in competing with Vibrio pathogens at higher salinities. The only high salinity document [Editor: This is a 2 MB file that’s slow to download and open!] that I could find is http://www.faculty.ait.ac.th/visu/Data/AIT-Thesis/Doctoral%20Thesis%20final/Dan%20Thesis%20%20pdf%202002.pdf. There does seem to be a gap in the research for papers on the application of probiotics at higher salinities. Total alkalinity is linearly related to salinity, so higher salinities should be just as stable or more stable.
Radhakrishnan Palasseri (email@example.com): Most commercial probiotics contain bacteria that work best in brackish waters, like estuaries, or in normal oceanic water. The hyper-saline waters of the Red Sea, for example, don’t support most probiotic bacteria.
If one applies molasses in hyper-saline conditions, will the most likely bacterial populations to develop be Vibrios?
Dallas Weaver (firstname.lastname@example.org): Remember, not all Vibrios are pathogens, some may be and probably are probiotic. [Editor: Check out this discussion on the Shrimp List. Dallas tells you how to grow your own probiotics, and why algal-based systems are better than bacteria-based systems in some situations.]
Jorge Cordova (email@example.com): Any ideas or comments on adding molasses to semi-intensive shrimp ponds? Can bio-floc systems be simulated in semi-intensive ponds by adding molasses and a low-protein diet—without aeration?
Dallas Weaver (firstname.lastname@example.org): Jorge, without aeration and mixing, carbon addition is a risky proposition. It’s easy to get anaerobic areas and hydrogen sulfide formation, which can crash the system. A few days of cloud cover and no wind, and you can get into big trouble. I prefer a lot more control when playing games with microbiology.
Brian Boudreau (email@example.com): Jorge, I agree with Dallas. If you want to take full advantage of what bio-floc systems can offer in semi-intensive shrimp ponds, you should consider supplemental aeration. Bio-floc technology almost goes hand-in-hand with intensive systems where the aeration cost is justified by greater production. Also if you don’t have pond liners, the supplemental carbon source is assimilated into the bottom sediment and not into the water column.
Patricio Buchell (firstname.lastname@example.org): Would it be possible to create bio-floc-like structures on the pond bottom? For instance with the use of organic matter such as compost (without manure) enriched with bacteria?
Brian Boudreau(email@example.com): That could work in a shallow, flow-through system where your organic matter was evenly distributed. It would require some oxygen in the water and would be especially nice if you could establish a population of marine worms, which make a great shrimp feed, under the organic matter.
Also, algal-based nursery ponds with short cycles and water exchange have been very productive using composts applied when the ponds were dry. After drying, the ponds are refilled, left alone for a week to develop a healthy food chain, and then stocked with postlarvae. The short cycle permits drying out on a regular basis.
Generally speaking, however, most ponds have some dissolved oxygen stratification occurring and keeping organics from building up on the bottom is considered important in keeping oxygen levels up. Even with aeration some high-fiber cellulose and organic carbon sources that do not degrade readily tend to drop out of the water column and accumulate in dead spots and deeper pockets on the bottom. This accumulation only has to be a couple of inches thick before it starts producing hydrogen sulfide. Shrimp tend to stay away from these zones, and the feed that accumulates in them further contributes to the build up.
Jorge Cordova (firstname.lastname@example.org): Brian, Dallas, thanks for your comments. Unfortunately aeration and liners are not a possibility for us. We tried molasses in small, easy-to-flush ponds that were one-meter deep and noticed a change in the algae that the shrimp were feeding on, but no dissolved oxygen problems. We had similar survival and growth rate in these ponds compared to regular ponds. We use the small ponds to test our ideas.
[In Ecuador], many farmers are adding molasses to their ponds, but there’s not a clear understanding of how it works, or if it works under extensive or semi-intensive conditions.
Indo-Gulf Shrimps (email@example.com): We agree with Jorge: The regular use of molasses in extensive and semi intensive ponds with or without aeration is common in many parts of the world. The use of molasses in these systems is to the tune of 10-20 kilograms once or twice a week while the feed given to the ponds varies from 300-600 kg per week. I don’t know if the addition of molasses has any effect on the overall pond environment.
Everyone agrees on the importance of C:N manipulation to get the most out of a pond, but the question is how, when and what quantities of molasses to use. Unsulfured molasses is recommended by some and some are using wheat flour or other grain flours as a source of carbohydrate. Some use fermented molasses with bakers yeast, others ferment the molasses with probiotics and urea.
David Griffith (firstname.lastname@example.org): Jorge, in the mid 1990s, LANEC was using composted fruit and vegetable wastes (mainly passion fruit) to stimulate organic productivity in semi-intensive ponds in Ecuador. A graduate student thesis on the use of organic fertilization demonstrated small but significant improvements in production through the application of the compost. Sadly the cost of producing the compost and transporting it to the farms outweighed the benefits, and I believe that the operation now uses more concentrated forms of carbon. It was a pretty nice way of managing the wastes though!
Dallas Weaver (email@example.com): Regarding the comments made by Indo-Gulf Shrimps: Correct, the percent of carbon being added is insignificant. It won’t change the C/N ratio enough to grow enough biomass to use significant amounts of nutrients.
Hernán Zambrano: (firstname.lastname@example.org): Hi Jorge, we use large quantities of probiotics in our pond water and feed. We haven’t had to use any antibiotics for four years, and our water and soil quality stay in perfect condition. On our farm we use molasses and micro minerals to grow our own probiotics. I think it is an efficient way to profit from molasses.
Sources: 1. The Shrimp List (a mailing list for shrimp farmers). Subjects: Organic Carbon Molasses, and Molasses. December 1, 2008, through January 29, 2009. 2. Bob Rosenberry, Shrimp News International. Update. March 22, 2017.
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