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To Lime or Not to Lime

Februay 6, 2012

 

This discussion took place on the Shrimp List, a free, email-based, bulletin board for the shrimp farming industry.  The discussion begins with a question about using nursery tanks to prevent whitespot during growout and then quickly evolves into a discussion about using lime in growout ponds.

 

Rodrigo Schveitzer (rschveitzer@yahoo.com.br): Does anyone have information on stocking specific-pathogen-free (SPF) postlarvae (PLs) in nursery tanks and then growing them until they reach a couple of grams before stocking them in growout ponds?  I want to produce bigger, healthier PLs that will withstand viruses during growout.

 

Anil Ghanekar (anilghanekar@yahoo.com): Dear Rodrigo, after a proper dry out and disinfection of your ponds, if you stock one-gram or larger SPF juveniles from a closed, bio-secure, recirculated nursery, you should be able to avoid whitespot mortalities, provided that you first disinfected the water in your growout ponds and protected the ponds from virus-carrying vectors, like birds and crabs.

 

Daniel Gruenberg (seagardenfoods@mac.com): Hi Rodrigo, in my humble opinion you are headed in the wrong direction.  It is known that whitespot cannot survive longer than a week without a host vector, so your management plan should account for this.  Why don’t you just let the ponds dry in the sun for ten days between cycles?  This requires no complicated nursery system, no investment and no management headaches.

 

In addition, I have my own theory about whitespot management, and I feel that SPF PLs and sterilization of pond benthos between cycles is not necessary.  If you concentrate on proper nutrition and reducing stress on your PLs, you will not see any significant problems—even if the virus is present.  Actually, I think whitespot is always present in the shrimp farming environment.

 

In my mind the single most important cause of whitespot is the use of lime to control pH.  We use no lime in our ponds, and we have been able to keep whitespot losses to less than 2% of production for five years.  Lime particles enter the shrimp’s gills resulting in osmotic stress that leads to a weak immune system.

 

Also, using PCR (polymerase chain reaction) testing on giant tiger shrimp (Penaeus monodon), I have found ponds with whitespot positive carriers that show no clinical symptoms of the disease.

 

I realize my opinion is controversial, but our production record speaks for itself.  We have often seen neighboring ponds that use a different management strategy succumb to whitespot while our ponds thrive and remain healthy.

 

Matthew B. (koygung101@yahoo.co.uk): Daniel, your theory on lime is quite interesting.  What is the pH in your ponds?  Perhaps it is high enough without lime.  In the presence of acid soils, it might be difficult to pull off your no-liming strategy.

 

Rodrigo, here in Thailand, it has been shown that if you use a nursery system and if you increase the water temperature to 32oC for at least seven days that you can permanently deactivate whitespot in the PLs, so non-specific-pathogen-resistant shrimp become whitespot free.  Therefore, you may want to consider integrating some form of heating into your nursery system.  Of course, you still have to keep the whitespot carriers out of the ponds, which is a different matter altogether.

 

Dallas Weaver (deweaver@mac.com): Daniel, Interesting hypothesis.  Lime is a nasty material when it comes in contact with a shrimp’s skin or gills.  With my recirculating systems, I always added lime in an area of the system without animals.

 

Daniel Gruenberg (seagardenfoods@mac.com): Hi Matt, we are able to keep the pH high enough even in acid soils through the management of the micro/macro nutrient balance.  Plankton creates the necessary alkalinity.  Not only that, but we have shown that the pH and other water quality parameters are more stable without lime.

 

Hi Dallas, Many years of careful observation has shown that in farms where the workers are throwing lime around the rim of the pond (just as they do the feed) seem to have a higher rate of whitespot mortalities.  I have been able to eliminate liming completely.  Of the thousands of pond/crop/cycles we have done without lime, I have had maybe two incidents of whitespot.

 

Ramon Macaraig (monmac52@yahoo.com): Daniel, algae in the ponds stabilizes the alkalinity.  When the algae soaks up the carbonates and bicarbs from the feed residues, the pH will definitely go up, and there may be no need for liming.  If you keep the algae population under control, the system will be more stable as long as you can keep out cyanobacteria.

 

Any verdict on pond salinity?  There are reports from Taiwan that polyculture of Penaeus vannamei with milkfish at a salinity of 5-8 parts per thousand and an algae transparency of 20-30 centimeters prevents whitespot flare-ups.

 

Rodrigo Schveitzer (rschveitzer@yahoo.com.br): Dear Anil, Daniel and Matt, thanks for the answers.  Daniel, what is your shrimp density and water temperature?  Do you treat your water with chlorine or other chemicals before stocking the animals?

 

Matt, what do you mean by “deactivating the virus”?  Do you eliminate the virus in the shrimp?

 

Anil, Daniel and Matt, do you believe it is possible to stock SPF shrimp that are negative for whitespot in a pond with no chemical disinfection and get good results?  Lined ponds would be a good strategy against whitespot, but not all farmers can afford them.  That was the reason I asked the original question about a nursery system.  It would cheaper to build a nursery than line the ponds.

 

Daniel Gruenberg (seagardenfoods@mac.com): Rodrigo, to answer your question about density and water temperatures: We harvest about 14 tons of 20-gram P. vannamei per hectare and about seven tons of 30 to 35-gram P. monodon per hectare.  Our water temperature is about 32°C in the summer, and it gets down to 23°C to 25°C in the winter.  We operate our farm organically and do not treat with chlorine or lime at all.  We want to keep the benthos “alive” in our production system.

 

Matt, if you empty the pond of all shrimps and let it dry in the sun for one week, the whitespot virus will be deactivated; you cannot eliminate it in carriers.

 

Jun Dajay (btd_sea@hotmail.com): When we receive PLs at our farm, we stock them in nursery ponds.  The idea is to give them two to three weeks of “rest”, while we observe them prior to stocking.

 

During the first month of growout, algae tends to dominate our ponds, but we don’t encourage it.  In fact, we discourage it by continuously supplementing the ponds with bacteria that make algae less dominant in the system.

 

We apply lime (agricultural and dolomite) on a regular basis every three days during growout.

 

Here in Vietnam, we were among the first few farms that stocked early in 2012, and while there are already farms that have had mortalities this week (January 23, 2012), we’re still doing fine after a month of growout.  Last year, diseases hit many ponds after about 20 days of growout.

 

Matthew B. (koygung101@yahoo.co.uk): Hi Rodrigo, holding P. vannamei PLs at 32°C for seven days does indeed appear to deactivate whitespot (you could say “kill” if you wanted), so yes, it does appear to actually work to clean up shrimp infected with whitespot.  I know the prevailing wisdom is that you cannot do this, but here in Thailand, our experience suggests otherwise.

 

Whitespot is very sensitive to high temperatures.  If you keep them high for a week or more, the virus appears to be disabled and does not cause mortalities when temperatures drop.  If high temperatures are maintained for too short a time, however, the virus is not disabled, and mortalities will occur when temperatures drop.

 

I agree with Daniel; you can stock whitespot-negative shrimp in in a whitespot infected area and get good harvest if you eliminate all (or at least most) the sources of stress.  The shrimp are perfectly capable of withstanding whitespot if they are not stressed by low oxygen levels, large fluctuations in pH and high levels of Vibrios in the system.  If these stressors can be controlled within optimal levels, then the shrimp can fight off whitespot quite easily.

 

Patrick Wood (patrickjwood@yahoo.com): Daniel, I don´t think your opinion is controversial at all—happy PLs, proper nutrition and reduced stress for successful cultivation is just common sense.  With ever-present viruses, I experienced that since before P. vannamei was domesticated.  We are up against vested interests that promote and sell preventative products.  The scientists have forgotten about the “art” of shrimp farming.  They use shock and fear to peddle their products.  It’s a shame there are so many gullible people out there.

 

D.V.S.N. Raju (dandu_raju169@yahoo.co.in): Hi Matthew, in northern Andhra Pradesh, India, I have seen conditions where only one of five or six ponds, which otherwise were managed identically, were hit by whitespot.  I don’t know why that happens.  In one case, the farmer was unable to drain his pond because he was in a disease-free area, so he gave the pond a big dose of chlorine, waited a month until the chlorine dissipated, restocked and got a good crop.  He also maintains a stress-free environment.

 

Zaid (ecotao@yahoo.com): Hi Dan, I find your experience with lime interesting.  In Saudi Arabia, we apply lime on our farm to maintain alkalinity above 100 parts per million.  In 2011, we were the only farm not to get whitespot and used more lime than any other farm.  I actually think lime may have been one of the factors that helped prevent whitespot.  A few publications support this view, but I have not seen any research showing a correlation between whitespot prevention and lime use.

 

Do you control alkalinity?  If yes, how do you do it without lime?

 

Also, we get “brown gill” in some ponds, and the only way to effectively treat it has been with hydrated lime.  Without lime, the gill problem persists once it gets a foothold, or I guess I should say a “gill-hold”.

 

Daniel Gruenberg (seagardenfoods@mac.com): Hi Zaid, pH/alkalinity control is critical to preventing whitespot.  I have a Chinese partner who taught me everything I know about shrimp farming.  He explained it this way: “Algae/photosynthesis produce alkalinity and bacterial action consumes alkalinity.”  If you attempt to stabilize alkalinity with lime, you run into two problems.  The first is potential damage to the gill structure (followed by osmotic stress), and the second is an unstable system that requires management inputs to maintain pH/alkalinity.  I have data from an experiment comparing lime-based pH control in our natural system.  Please contact me privately and I will send you the data.  It shows that with the lime system the pH ranged from 7.5 to 9.0, along with rapid changes after rains.  Since we achieve a balance between the production and consumption of alkalinity, the pH stays within a much narrower range (7.8 to 8.5) with no abrupt changes.

 

The lime/whitespot relationship was not something we evaluated scientifically; it evolved after many years of observation and trial and error.  We have developed our own natural alkalinity control system that uses micronutrients to maintain the proper balances between bacterial and algae species in the pond.  We have helped farms stabilize production with this system through thousands of pond cycles, and our whitespot rate is less than 2% over the long-term.

 

Zaid (ecotao@yahoo.com): Hi Daniel, from the biofloc studies that have been published, the effect of photosynthesis on alkalinity appears to depend on the type of fertilizer used.  A study in the journal Aquaculture (Volume 257, Pages 346–358, Year 2006) says: “The biosynthesis of saltwater algae can be described in general by the following stoichiometric* relationships...for ammonia as the nitrogen source.  ...Note that 3.13 grams of alkalinity (as CaCO3) is consumed for every gram of ammonia–nitrogen consumed in the first relationship and 4.02 grams of alkalinity (as CaCO3) is produced for every gram of nitrate–nitrogen consumed in the second.”

 

Urea is converted to ammonia, so unless you use sodium nitrate as a fertilizer, it appears the bulk of the remaining fertilizers will lead to reduced alkalinities.

 

* Wikipedia: “Stoichiometry is a branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions.  In a balanced chemical reaction, the relations among quantities of reactants and products typically form a ratio of whole numbers.  For example, in a reaction that forms ammonia (NH3), exactly one molecule of nitrogen (N2) reacts with three molecules of hydrogen (H2) to produce two molecules of NH3: N2 + 3 H2 → 2 NH3.”

 

Daniel Gruenberg (seagardenfoods@mac.com): Zaid, That is an oversimplified view of what is going on in a pond.  You have interactions among the nitrifying bacteria, denitrifying bacteria, blue-green algae, chlorella, diatoms and the higher zooplankton species like rotifers and copepods.  Some of this takes place in the pond water and some takes place in the benthos.  In such a complicated system, you can’t use stoichiometric relationships established in single species systems.

 

Empirically, there is continuous nitrogen input into the system via the feed, and pH shoots up to over nine when the overall feeding rate is low early in the cycle.  Then it stabilize between 7.8 and 8.5 late in the cycle.  If your simple stoichiometric relationship held in a complex pond ecosystem, then yes, you would see alkalinity and pH drop over time.

 

The fact that we don’t see the drop in alkalinity or pH is proof that the claimed stoichiometry from your cited paper does not hold in pond conditions.  Actually, the ammonia, nitrite and nitrate and algae species in pond water can use any of these forms of nitrogen.

 

Zaid (ecotao@yahoo.com): Hi Daniel, I am not convinced that whitespot has a negative correlation to lime use in shrimp ponds or that liming is a detrimental aquaculture practice.  Your empirical conclusions are different from mine.  Most of the information that I have collected seems to indicate a decline in alkalinity in shrimp ponds.  For example, in 2012, a study in Aquaculture, “Farming Aquatic Animals and Plants, 2nd Edition”, discusses the “calcium carbonate equivalence of feed” and concludes “nitrification can cause pH and alkalinity to rapidly decline.”  Admittedly, this is in intensive water re-use systems.

 

Probably, many stable water quality management systems can be developed and each will be successful.  You have developed a system that does not need lime.  It would great if some solid research publications looked at the beneficial versus detrimental use of lime.  Even though we have a high-exchange, high-alkalinity, flow-through system using full-strength seawater, when measuring alkalinity, we find a difference and a decline in some ponds.  We have not identified the exact biological process resulting in this decline, but as natural seawater has an alkalinity of well over 100, whenever the alkalinity in a pond falls below 100, we apply lime.  Application of lime is not supposed to have an effect on alkalinity at these levels, but after CaCO3 lime application the alkalinity does increase.

 

Our system is very “traditional” and unsophisticated, utilizing lime and molasses during the growout cycle, with organic and inorganic fertilizers at the beginning of the crop and water exchange.  Farms on the Red Sea in Saudi Arabia have to exchange water to manage salinity.  During a period when whitespot was highly prevalent, we did not get whitespot and did use lime.

 

Shrimp News: Hi guys, great discussion.  I don’t pretend to understand any of this; I just straighten out the writing a little bit so that everything hangs together.  If I made mistakes, let me know, and I’ll fix them.  One of the great things about online publications is that your can go back and correct your mistakes and typographical errors.

 

Sources: 1. The Shrimp List (a mailing list for shrimp farmers).  Subject: Nursery Tanks in WSV Affected Farms?.  January 22 to 31, 2012. 2. Bob Rosenberry, Shrimp News International, February 5, 2012.

 

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