Sediment Oxygen Demand in Shrimp Ponds

A Discussion from The Shrimp List

Ajitsinha (panchamaqua@vsnl.com): Can pond probiotics reduce sediment oxygen demand?

Dallas Weaver (deweaver@scientifichatcheries.com), a PhD aquaculture consultant that specializes in water chemistry, feeds and closed systems, answers that question and many more:

In general, no.  Unless the probiotic decomposes the organic waste before incorporation into the sediment, it won’t impact the flux of carbon into the sediment.  If it does decompose the organics before it gets into the sediment, it uses oxygen from the water column.  You don’t win in terms of oxygen levels in the water.

Ajitsinha (panchamaqua@vsnl.com): Please explain the “flux of carbon into the sediment”.  Also, will the addition of molasses shift some nitrogen mineralization from the sediment into the water column?

Dallas Weaver (deweaver@scientifichatcheries.com): Organic material (referred to as carbon) tends to move into the soil by a normal mixing process called “bioturbation”.  It is this organic material input that provides the source of oxygen demand in the soils and when there is too much organic material relative to the rate that oxygen can diffuse into the soil, this organic material can provide the carbon for nitrate destruction.  When the nitrate/nitrite is gone, sulfate will be reduced resulting in hydrogen sulfide formation.

Adding molasses stimulates bacterial growth in the water column, and the bacteria support an ecology of organisms that convert the ammonia into protein.  The molasses provides the energy for this food chain just like sunlight provides the energy for the algae growth (which also converts ammonia, nitrate, nitrite into protein).  Hopefully some of this protein then flows through the feed chain to your shrimp.  If anything, adding molasses to the water will decrease the rate of bacterial mineralization of ammonia to nitrite and nitrate.

Part of the impact of molasses is the growth of nonpathogenic bacteria which support a whole food chain of bacteria eating organisms.  Many of these organisms that are feeding on nonpathogens will also eat the potential shrimp pathogens, which is a good outcome.

Patricio Bucheli (p_bucheli@hotmail.com): Dr. Weaver, your explanation on how molasses works as an “energy source” is very clear.  Regarding that fact, do you know how we can measure or define the amount of molasses to use?

Dallas Weaver (deweaver@scientifichatcheries.com): I have produced protozoans, rotifers and other small live food items using molasses and other carbohydrates as the energy sources.  I needed very high productivity per unit volume.  Photosynthesis is limited to about 10 grams of carbon fixation per square meter per day.  I needed about 100 to 300 grams.  I was producing 3 to 5 kilograms of live rotifers a day.  In these systems, I used a mix of dry yeast and fish meal as feed for the organisms and added carbohydrate (molasses, sugar, dextrose, lactose, acetate, fine cellulose or cornstarch as the energy source) to drive the microbial ecology, along with some trace nutrients (vitamins and minerals) and lipids.  These systems were heavy oxygen burners (some were equipped with pure oxygen) and required a lot of aeration per unit volume.  With the large amount of carbon being used in the system, the pH tended to be low (down around 7.0, I also had active pH controllers on the system, both high and low) and the carbon dioxide was fairly high.  With the low pH, I could let the ammonia run at about 1 to 2 parts per million and adjusted the carbon/nitrogen (C/N) ratio of the feed/carbohydrate mix to control the ammonia.  I use a computer program to do all the C/N calculations and then provide the operators of the systems with information on changes in the ammonia readings and their rate of the change.

In a pond situation where much of your energy is from sunlight and your microbial ecology doesn’t flow as directly into your target organism, the problem is a little more difficult.  I would be tempted to use a small amount of molasses for the probiotic impact and not add a lot more except when the ammonia or nitrite approach detrimental levels at your pH (> 20 µg/l as N, for unionized ammonia).  You want to help the growth of nitrifying bacteria and elevate the nitrate levels in the system (this will help oxidize the organics in the sediments and prevent hydrogen sulfide formation) by maintaining a total ammonia nitrogen (TAN) level greater than 0.3 ppm total ammonia nitrogen, but less than 3 ppm, depending on the pH.  I would also do molasses feeding in the morning to help minimize the diurnal pH swing in the pond.

I hope this helps a bit in understanding the dynamics of these systems.  You have to think through all the details to keep this complex microbial ecology from crashing.

D. Ramraj (padlab@yahoo.com): The low and medium density shrimp ponds in the tropics are typically photoautotrophic systems with high diurnal fluctuations in pH, alkalinity and dissolved oxygen.  How effective will the addition of a carbon source be in stimulating the heterotrophic bacteria in lower density ponds?  How will it affect the use of probiotics?

While the water column tends to be photoautotrophic, pond sediments become anaerobic a short time after stocking.  Given the size of the ponds and the aeration methods it may not be possible to reverse this condition until harvest.  Even if the column shows acceptable dissolved oxygen (DO) levels, the shrimp (which are benthic) would probably be stressed due to high sediment DO demand.

Is there a way to reduce the sediment oxygen demand?  Will older ponds (after several crops) tend to have more oxygen demand in their sediments?  Will probiotics be effective in reducing the organic load and sediment DO demand if they are used in pond sediment prior to stocking?

We have noticed improved production, growth rates and carrying capacities in ponds that were cultured after lying fallow for long periods.  Can this be due to lowering of sediment organic load and the sediment DO demand?

Dallas Weaver (deweaver@scientifichatcheries.com): One of the more harmful impacts of an anaerobic bottom is the potential for generating hydrogen sulfide.  If you can keep the nitrates higher, this will help suppress the sulfide forming bacteria and have some impact on the oxygen consumption rate of the pond bottom.  The nitrate oxidizes some of the organic carbon in the bottom.

To get higher nitrates in the water column you need to either add nitrate as NaNO₃, a calcium form, and/or get more nitrification in the water column.  To achieve the latter, you have to decrease the water exchange to almost zero, if you want some of the nitrification to occur in the water column.  Nitrifying bacteria are slow growing and water exchanges of greater than 7-10% a day can eliminate water column nitrification activity.

When the nitrate concentration is higher than the oxygen concentration, the nitrate will diffuse into the sediments and bacteria will use it as an electron acceptor to oxidize the organic material in the sediments.

Organic material tends to build up in the pond bottoms at high feed rates.  Fallowing, draining and then plowing the pond can really oxidize a lot of material fairly fast.  You have to get the pond bottom dry enough to plow—so that the soil has air spaces between the particles—but not so dry that the soil is lifeless.  To get oxygen into the pond bottom, it’s all about moisture and texture control.

Given that decomposing bacteria are everywhere, the chances of your ponds being free of decomposing bacteria are very small.  Probiotics probably won’t have any significant impact on sediment oxygen in used ponds.

I have often speculated about, but have never tested, the concept of creating a small, deep, shaded, aerated pond to grow a good culture of nitrifying bacteria by feeding the pond ammonia or urea and maintaining a concentration of 1 to 3 ppm TAN.  Towards the start of a new crop, you could add some of this water to the pond along with some ammonia to feed the bacteria.  This would give nitrification a head start.  One of the problems with a pond is that for the first six weeks, or so, you may have very little ammonia in the water as the algae growth keeps up with the production from the feed and shrimp (assuming the pond is starting with new water).  Towards the end of the cycle, the ecology is starting to recycle the ammonia as the algae reaches its maximum density and you may start seeing ammonia and the nitrifying bacteria, but a little too late.  With a doubling time measured in several days to a week, without a large number initially, the nitrifying bacteria numbers won’t increase fast enough to keep up with the production of ammonia.

D. Ramraj (padlab@yahoo.com): Nitrate levels tend to be lower than DO levels in ponds with phytoplankton blooms and frequent water exchanges.  Most nitrate compounds will dissolve in the water column and may not be available to the sediment.  The challenge is to deliver the nitrate into the anaerobic sediments.  Is there a nitrate compound that can settle to the bottom and release nitrate slowly?

Dallas Weaver (deweaver@scientifichatcheries.com): There is no way to build up nitrate with a lot of water exchange.  With slow growing bacteria, the exchange rate is often the controlling factor.

Having the nitrate in the water column is fine, it will diffuse into the sediments.  If the concentrations are higher than the DO, the mass flow into the sediments can be faster than the oxygen.  In a way, the nitrification of ammonia stores oxygen from the water column in the form of nitrate, which then transports the oxygen into the sediments and oxidizes the organic carbon in the sediments.  This allows you to have a higher carbon flux into the sediments without hydrogen sulfide formation.

Ajitsinha (panchamaqua@vsnl.com): Assuming that we are able to manage the nitrate level in water column, what is its desirable level?

Dallas Weaver (deweaver@scientifichatcheries.com): It depends on what you are growing.  With shrimp, the nitrate toxicity is very low—on the data that I have seen.  In recycle systems operating at 50+ ppm, I had no nitrate problem with Penaeus vannamei.  That range would give a lot more oxidizing power to the sediments.

Ajitsinha (panchamaqua@vsnl.com): In our shrimp ponds the nitrate levels are normally less than 0.1 ppm.  The secchi disc readings are less than 20 cm.  Algae is abundant and appears to be consuming the nitrate.  Under these conditions what can I do to raise the level of nitrate?

Dallas Weaver (deweaver@scientifichatcheries.com): You are in a difficult position.

What’s your ammonia reading?  Do you have hydrogen sulfide in the sediments?  What is your morning and afternoon pH?  Also what is your equilibrium pH (take a small sample and aerate it for at least two hours, until the pH stabilizes)?  What is your measured alkalinity?

Ajitsinha (panchamaqua@vsnl.com): We do not monitor hydrogen sulfide.  One pond water sample had a pH of 8.8.  It stabilized at 8.5 after aeration.  Below you will find summarized values (minimum/maximum/average) for some of the parameters in our 11 ponds over a period of over 150 days.

Alkalinity = 70 to 110 ppm (as CaCO₃)

Ammonia = 0.35 to 0.05 ppm

Nitrite = 0.18 to 0.05 ppm

Nitrate = 0.08 to 0.015 ppm

Total Phosphorus = 0.48 to 0.35 ppm

pH = 7.5 (at 7 a.m.) to 9.2 (average 8.00)

Diurnal pH Variation = 1.0 to 0.30

Secchi Disc Reading = 10 to 40 cm (average 20)

Source: The Shrimp List (a mailing list for shrimp farmers, “shrimp-subscribe@yahoogroups.com”).  Subject: [shrimp] Sediment Oxygen Demand.  January 2–13, 2008.

Country Reports

Australia

$35 Million Shrimp Farm

Pacific Reef Fisheries has received conditional permission to build a new shrimp farm with 259, one-hectare ponds in northeast Queensland at a cost of $35 million.  The farm would add nearly $19 million and more than 200 jobs to the economy during construction.

At peak production of 1,600 tons, the farm would increase Queensland’s farmed shrimp production by 50 percent.  To limit the impact of effluents, the farm will be required to meet strict environmental and operating guidelines, including $2 million worth of sand filtration technology to treat wastewater from 47 hectares of settlement and water treatment ponds.  In addition, to mitigating sediment and nutrient runoff, the farm must offset the project’s impact on nearby Abbot Bay by rehabilitating a 240-hectare area of degraded and weed-infested land near the farm’s site on the Elliot River.

With this farm and its other farm in Ayr, Queensland, Pacific Reef Fisheries will become one of the biggest shrimp farms in Australia.  It plans to grow banana (Penaeus merguiensis), black tiger (P. monodon), brown tiger (P. esculentus) and kuruma (P. japonicus) shrimp.

The proposed farm includes high-tech processing facilities and on-site accommodations for employees.  It will take four years to build and hopes to produce 550 tons in its first year.

The farm needs a final environmental permit before it can begin construction.

The North Queensland Conservation Council says the proposed shrimp farm could be an environmental disaster.  The council’s James McLellan says the world’s best practice in shrimp farming is zero discharge and lined ponds, which this farm will not have.

Sources: 1. BYM Marine Environment News.  Australia/Guthalungra prawn farm passes muster (http://bymnews.com/news/newsDetails.php?id=21021).  January 11, 2008.  2. ABC News.  Green group questions giant prawn farm plans (http://www.abc.net.au/news/stories/2008/01/15/2138757.htm).  January 15, 2008.

Australia

Shrimp Prices Could Double

Shrimp prices could double and supplies run short as strict new quarantine rules stop the import of inexpensive farmed shrimp from Asia.

Source: Geelong Advertiser.  Prawn costs set to soar (http://www.geelongadvertiser.com.au/article/2008/01/09/10345_news.html).  Martin Watters.  January 9, 2008.

Indonesia

Shrimp Exports Drop Slightly in 2007

In 2007, Indonesia’s shrimp exports dropped two percent, to 88,000 tons valued at $545.9 million.

Maritime and Fisheries Minister Freddy Numberi said Indonesia’s fishery products had a difficult time competing in international markets after the imposition of new quality standards by a number of the importing countries.  Numberi noted that demand in the domestic market rose significantly and offset the decline in the export market.

Fish Breeding Director General Made L. Nurdjana said the country’s shrimp production in 2008 would be higher than the 320,000 tons produced in 2007.

Source: Seafood.com (an online, subscription-based, fisheries news service).  Shrimp led decline in Indonesia’s 2007 seafood exports.  Ken Coons (phone 781-861-1441, email kencoons@seafood.com).  Editor and Publisher, John Sackton (phone 781-861-1441, email jsackton@seafood.com).  January 9, 2008.

Mozambique

$1 Million for Sustainable Mollusk and Shrimp Farming

With a $1 million grant from the Canadian International Development Agency (CIDA), a Southern Oceans Education and Development (SOED) project at Canada’s University of Victoria will establish sustainable shrimp and mollusk aquaculture programs in Mozambique that are designed to preserve the coastal ecosystems.

SOED will build on expertise developed during previous CIDA-funded projects in Brazil.  Since Mozambique and Brazil share a common language (Portuguese) expertise can easily be shared between institutions in Brazil and the School of Marine and Coastal Sciences at the satellite campus of Eduardo Mondlane University (UEM) in the coastal city of Quelimane, Mozambique.

Under the co-direction of the University of Victoria, SOED will help develop instructional programs in marine sciences, oceanography and aquaculture at UEM.  Graduate students from UEM and the Ministry of Fisheries will study marine sciences at the University of Victoria and at Brazil’s Federal University of Santa Catarina (UFSC), where the University of Victoria has a long-standing partnership.  Graduating students will go back to Mozambique to create courses at UEM and develop effective policies for the management of coastal resources.

Along with UFSC, the University of Victoria will provide expertise to develop aquaculture extension programs for citizens interested in operating their own aquaculture businesses.  Aquaculture provides many business opportunities for women since cultural activities take place close to home and draw on their traditional skills.  Even children, who often assist in family occupations, will be able to participate in the aquaculture business without having to forfeit attendance at school.

Source: The Ring.  Developing sustainable aquaculture in Mozambique (http://ring.uvic.ca/08jan10/aquaculture.html).  Patty Pitts.  January 2008.

The Netherlands

Happy Shrimp Farm

Happy Shrimp Farm, the brainchild of entrepreneurs Gilbert Curtessi and Sebastian “Bas” Greiner, uses thermal effluent, a big greenhouse and recirculating raceways to raise western white shrimp (Penaeus vannamei) in Rotterdam.

Curtessi and Greiner plan to build three new farms in Germany (Berlin, Munchen and Hamburg), all located near power plants.  “All we need are big cities where you can find both residual industrial heat and a consumer market for fresh shrimp,” explains Curtessi.  Their goal is to have 25 Happy Shrimp Farms up and running across Europe within five to ten years—and they are already looking beyond Europe to expand their concept.

In July 2007, Happy Shrimp harvested the first crop from its farm in Rotterdam and auctioned some of it off during a festive ceremony called “Night of the Prawns”, generating more than $36,000, which will be donated to the World Wildlife Fund (WWF).

In a cooperative venture Happy Shrimp has an agreement with Taste of Nature BV and Koppert Cress to grow sea lavender and glasswort, salt-tolerant vegetables, in racks above the fish tanks.  Curtessi says, “This approach shows that certain types of fish and shrimps can be grown in combination with agricultural vegetables....  This makes an existing production facility more efficient because water and heat can be reused.”  The steady climate conditions in the greenhouse make it possible to produce vegetables year-round.

Source: Feed Mix.  Sustainable tropical shrimps from Rotterdam.  Volume 15, Number 6.  2007.

Taiwan

Save Money on Your PCRs

PCR (polymerase chain reaction) has long been a popular method for diagnosing shrimp viruses.  A new technique, however, called “isothermal amplification”, provides nested PCR sensitivity at a much lower cost.  It has been tested on several shrimp viruses, including WSSV, TSV and IHHNV.  It is sensitive down to 10 viral copies, provides results in two to three hours and costs only $500, compared to $20,000 for PCR equipment.

The first commercialized isothermal diagnostic system, “I-Screen”, was launched at the end of 2007.  I-screen kits are currently available for WSSV and TSV; others will be available soon.  Combining simplified extraction and post-amplification detection methods, the diagnostic procedures for I-screen require no formal training and can be done at pond side.

Information: If you are interested in distributing this product in Latin America (except for Mexico, Panama and Brazil), contact: Su Chen, Chief Operating Officer, GeneReach Biotechnology Corp., No. 2-1, 7th Road, Taichung Industrial Park, Taichung, 407, Taiwan (phone 886-4-23580768, fax 886-4-23580769, email iq2000@ms36.hinet.net, webpage http://www.i-screen.com.tw).

Source: Email to Shrimp News International from Chen Su on January 10, 2008.

United Kingdom

Prawnfresh, a Metabisulphite Substitute

On January 9, 2008, the UK seafood industry was warned by The Sea Fish Industry Authority (Seafish, supported by the UK government to promote good quality, sustainable seafood) not to use XyRex products, including Prawnfresh, a metabisulphite substitute, until further notice.

Following a decision by the Food Standards Agency (FSA), the use of XyRex products for decontaminating fish and fishery products must be considered illegal, Seafish said.

XyRex’s Prawnfresh is widely used throughout the UK for treating blackspot in shrimp and was included in Seafish trials in November 2005 as an alternative to the use of sodium metabisulphite.  Alternatives to sodium metabisulphite were investigated because sulphites can have adverse effects on workers handling the chemical and because foods with added sulphite require allergen labeling.

“It was understood for these trials that the FSA had classified Prawnfresh as a food processing aid...a chemical with a technological function during processing, but which leaves no harmful residue in the end product,” a statement issued by Seafish said.

On December 21, 2007, FSA issued a statement informing industry that XyRex brand products are being marketed and used for decontaminating fish and fishery products in the UK.  It said that since the products are not approved by the European Commission, their use is in breach of Article 3 of EU Regulation No. 853/2004.

XyRex is said to be urgently contesting the issue.

Source: FishUpdate.com.  Warning issued over fish decontamination products (http://www.fishupdate.com/news/fullstory.php/aid/9648/Warning_issued_over_prawn_blackspot_product.html).  January 9, 2008.

United States

Florida—Shrimp Farming Sessions at the WAS Meeting in Orlando

Scheduled for February 10-12, 2008, “Aquaculture 2008” in Orlando will have three days of shrimp farming sessions.  For the complete shrimp program and registration information, click the above link.

Source: Bob Rosenberry, Shrimp News International, January 15, 2008.

Vietnam

Green-Pincered Shrimp

Almost 5,000 hectares of ponds are being used to raise green-pincered shrimp [most likely Penaeus semisulcatus, the green tiger shrimp] in the Mekong Delta, a ten-fold increase over the past five years.

Most of the ponds are located in provinces along the Tien and Hau rivers.  Ben Tre Province has 2,400 hectares of green-pincered shrimp farms, Dong Thap Province has 1,500, An Giang Province has 600, and Can Tho Province has 400.  The local farmers usually raise green-pincered shrimp in combination with rice or in rotation with giant tiger shrimp.

The expansion of green-pincered shrimp farming is attributed to the stable supplies of broodstock, improved husbandry and increasing consumer demand.

Source: The FishSite.  Mekong Delta On Target to Be Top Shrimp Producer (http://www.thefishsite.com/fishnews/6079/mekong-delta-on-target-to-be-top-shrimp-producer).  January 11, 2008.

Vietnam

Seaprodex Minh Hai

The Minh Hai Joint Stock Seafood Processing Company (Seaprodex Minh Hai) has inked a long-term contract with a USA partner for the delivery of 10 to 15 containers of processed shrimp a month, according to the Vietnam Association of Seafood Exporters and Producers.  Seaprodex Minh Hai exported $58 million worth of seafood in 2007, said director Tran Thien Hai.

Source: VietnamNetBridge.  More tiger prawns exported to US (http://english.vietnamnet.vn/biz/2008/01/763326/).  January 9, 2008.

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