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March | April 2012

Feature title: PRODUCT SHOWCASE 2012

The International magazine for the aquaculture feed industry

Thepropermanagementofpondwaterqualityplays a significant role for thesuccess of aquaculture operations.Each water quality parameter alone

candirectlyaffecttheanimals´health.Exposureof shrimp and fish to improper levels of dis-solved oxygen, ammonia, nitrite or hydrogensulfide leads to stress and disease. However,in the complex and dynamic environment ofaquaculture ponds, water quality parametersalsoinfluenceeachother.

Unbalanced levels of temperature andpH can increase the toxicity of ammoniaand hydrogen sulfide. Thus, maintaining bal-anced levels of water quality parameters isfundamental forboth thehealth andgrowthof culture organisms. It is recommended tomonitorandassesswaterqualityparametersonaroutinebasis.

In this article the most important water

qualityparameterssuchasoxygen,pH, tem-perature,salinity,turbidityandnitrogencom-pounds are described with insights on howtheseparametersinfluenceeachother.Table1 gives an overview of the water qualityparameterswiththeirstandardvalues.

Dissolved oxygen (DO) is one of themost important parameters in aquaculture.Maintaining good levels of DO in the wateris essential for successful production sinceoxygen (O2) has a direct influence on feedintake, disease resistance and metabolism. Asub-optimal level isverystressful for fishandshrimp.ItisthereforeimportanttokeepDOatoptimumlevelsofabove4.0ppm.

Thedynamicoxygencycleofpondsfluctu-atesthroughoutthedayduetophytoplanktonphotosynthesisandrespiration(Figure1).

As shown in Figure 1 maximum DOwill occur in the late afternoon due to thebuildupofO2duringthedaythroughphoto-

synthesis. As phytoplankton(microscopic algae) usuallyconsumes the most O2 andsince photosynthesis doesnot occur during the night,DO levels decline. Criticallylow DO occurs in pondsspecificallywhenalgalbloomscrash. The subsequent bac-terial decomposition of thedead algae cells demands alot of oxygen. Managing theequilibriumofphotosynthesisandrespirationaswellasthealgae growth - is an impor-tanttaskinthedailyworkofafarmer.

When feeding the fishand shrimp, oxygen demandis higher due to increased

energy expenditure (also known as specificdynamic action). To face this higher oxygendemand,severalmeasurescanbetaken:

Other sources of oxygen than photosyn-thesis are diffusion or transfer from air towater. Wave action or mechanical aerationis forcing this oxygen diffusion. Paddlewheelaerators accomplish this by breaking waterinto small droplets and increasing contactof water surface with air. Aspirator aeratorscompelair intothewater throughaventureandapropeller.Anotherreasonforaerationis the circulation of aerated water throughthepond.

Biochemicaloxygendemand(BOD)ofthepond can affect the oxygen cycle and thus,theoxygenequilibrium. Five-daybiochemicaloxygen demand (BOD5) is the amount ofDO needed by aerobic biological organismsinthewatertobreakdownorganicmaterialpresent at a constant temperature during a5-dayperiod.

BOD5 is an importantwaterquality vari-able that may be required to demonstratecompliancewithwaterqualitypermits issuedby the governments and to achieve farmcertification.

The BOD5 of pond aquaculture efflu-ents usually ranges from 5 to 20 mg/l. Thegreater the BOD, the more rapidly oxygenisdepleted.

Also,theO2cycleandthus,theDOlevelscan be affected by changes in the environ-ment; a cloudy day will diminish the photo-syntheticO2 input toDO.Correspondingly,uncommonlyhightemperatureswilldecreasethesolubilityofO2inwaterandhencelowerDO.Whenapondisin“equilibrium”DOwillnotchangedrastically.

Temperature is another important waterqualityparameter.Itcanaffectfishandshrimp

table 1: Water quality parameters and their standard values

Parameter Standard values

(Dissolved) oxygen >4.0 mg/l

temperature Species dependent

pH 7.5 – 8.5

Salinity Freshwater: < 0.5 pptBrackishwater: 0.5 – 30 pptSaltwater: 30 – 40 pptoptimum: 15 – 25 ppt

Carbon dioxide (Co2) < 10 ppm

ammonia (nH4+/nH4-n) 0 – 0.5 ppm

nitrite (no2-) < 1 ppm

Hardness 40 – 400 ppm

alkalinity 50 – 300 ppm

H2S 0 ppm

BoD < 50 mg/l

Monitoring pond water quality to improve shrimp and fish productionby Elisabeth Mayer MSc, BIOMIN Holding GmbH, Austria

38 | InternatIonal AquAFeed | March-april 2012

FEATURE

March-april 2012 | InternatIonal AquAFeed | 39

metabolism, feeding rates and thedegreeofammonia toxicity. Temperature also has adirect impact on biota respiration (O2 con-sumption) rates and influences the solubilityof O2 (warmer water holds less O2 thancoolerwater).

Temperature cannot obviously be con-trolled in a pond. Aquatic animals modifytheir body temperature to the environ-mentandaresensitivetorapidtemperaturevariations.Foreachspecies,thereisarangeof temperature conditions (Table 2). It isthereforeimportanttoadaptfishandshrimpprogressively when transferring them fromtanktopond.

Carbon dioxide (CO2) in ponds is pri-marily produced through respiration by fish/shrimpandthemicroscopicplantsandanimalsthatconstitutethepondbiota.

Carbondioxide levels (and toxicity)arehighestwhenDOlevelsare lowest(Figure2).Thus,dawnisacriticaltimeformonitor-ing DO and CO2. High CO2 concentra-tions inhibit the ability of fish and shrimptoextractO2fromthewater,reducingthe

tolerancetolowO2conditionsand inducing stress comparabletosuffocation.

AnincreaseinCO2mayalsodecreasethepH,whichcanleadto toxicity of nitrite. If plants inthewaterabsorbtoomuchCO2forphotosynthesisduringtheday,the pH will increase, and thefish and shrimpare subjected tohigherun-ionizedtoxicammonia(NH3)concentrations.

Carbon dioxide concentra-tions above 60 ppm may belethal. In an emergency,CO2canberemovedbyadding limingagentssuchas quicklime, hydratedlimeorsodiumcarbonatetothepondwater.

pH is a measure ofacidity(hydrogenions)oralkalinity of the water. Itis important to maintaina stable pH at a saferange because it affectsthemetabolismandotherphysiological processes of culture organisms.Itcancreatestress,enhancethesusceptibilityto disease, lower the production levels andcause poor growth and even death. Signsof sub-optimalpH are besidesothers increasedmucusonthegillsurfaces of fish,unusual swim-ming behavior,fin fray, harmto the eye lensas well as poorphytoplanktonandzooplanktongrowth.OptimalpH levels in thepond should bein the range of7.5–8.5.

The CO2concentrationin the wateralso influencesthe pH, e. g. anincrease inCO2decreases thepH, as alreadymentionedabove (Diagram1). As phyto-plankton in thewater utilizesCO2 forphoto-synthesis,thepHwill vary natu-rally throughout

daylight hours. pH is generally lowest atsunrise (due to respiration and release ofCO2 during the night) and highest in theafternoonwhenalgaeutilizationofCO2isat

table 2: temperature (°C) conditions for aquatic species

Species lower lethal temperature

Preferred temperature

Upper lethal temperature

rainbow trout 0 13 - 17 24 - 27

nile tilapia 8 - 12 31 - 36 42

tra catfish 9 23 – 27 33

Crucian carp 0 25 - 32 38

Channel catfish 9 22 – 29 37

Cobia 1 21 - 27 33

tiger prawn 14 25 - 30 36

White shrimp 14 > 20 40

table 3: toxicity of H2S to various aquatic organisms

Common name Species name lC50 (ppb)

Channel catfish Ictalurus punctatus 846.7

Indian prawn Penaeus indicus 179.3

oriental river shrimp Macrobrachium nipponense 51.0

Crab Portunus trituberculatus 31.5

Black tiger shrimp Penaeus monodon 62.6

Pacific white shrimp litopenaeus vannamei 60.2

Figure 2: The daily cycle of oxygen and carbon dioxide in a pond

Figure 1: The daily cycle of oxygen in a pond

Diagram 1: CO2 and pH correlation, influencing the toxicity of NH3

38 | InternatIonal AquAFeed | March-april 2012 March-april 2012 | InternatIonal AquAFeed | 39

FEATURE

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The UK’s major Aquaculture exhibition and conference

featuring the latest aquaculture products and innovations.

Visit www.aquacultureUK.com for further information or

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Fish_Farming Int_1/8_107X146.indd 1 17/10/2011 12:45

feeding started in the country in late 1990swhensemi-intensiveshrimpfarmingofbrack-ishwater started in thesoutheasternpartofthe coastal area and in the beginning of lastdecadeinfreshwater,whenThaicatfishfarm-ingstartedgettingpopular.

Beforethatafewfarmsusedricebranandoilcakesmashfrominaquaculture.

Supplementalfeedsinpelletformforsemi-intensive Peneaus monodon farming weremostlyimportedandajointventurecompanystarted producing several thousand tonnesannuallyinthecountry.

However, semi-intensive Peneaus mono-donfarmingstartedandvanishedlikebubbles,aquaculturefeedimportsceasedtoexistandthe joint venture company switched overto producing low-cost aquaculture feeds forfishes.

Since than pellets became familiar andseveral companies and private farm ownersarenowproducingpelletsforfishandshrimpin the way they like. Most of the pelletsproduced as feed contains more junks thannutritionallyrequiredproportionalingredients.Improper feedsprovided toa terrestrial ani-malmaycauseharm to itor theanimal candeny consuming andprovider has anoptiontochangeormodify tomake itpalatable. Incaseofaquacultureoncefeed(sinking)ispro-vided,itisdifficulttoknowthatpercentageoffeedbeingconsumedbytargetanimal.

The impact of poorer quality feeds

To make things worse uneaten feed/particlespartlyusedasfertiliserinaquaticeco-system and pollute the water body rapidly,if water exchange is not practiced (Tacon,1996).InBangladeshaquaculturemostpondsarerainfedandhardlyhasanyscopeofwaterexchange.

Therefore, cost effective quality feed is amustforaquaculture.

Bad quality feed translated into poorerproductionperformance,polluteswaterbod-ies,degradeeco-systemandenvironmentandmay leadtooutbreakofdisease inaquacul-turefarms(Baruaetal,2011).

It is very much difficult to find out thetimewhenformulatedfeedwasintroducedinaquafarmsofBangladesh,butitiswellknownthatduringtheintroductionofsemiintensivemethodsupplementaryfeedwasintroduced.

EspeciallyinshrimpfarmslocatedinCox’sBazaar used fishmeal, rice bran anddifferenttypes of oil cakes as supplementary feed.Local farmer started to use this mixturein 1987-1988. The Meghna Farm of Cox’sbazar first used the pelleted feed in 1989.SaudiBangla FishfeedLtd, firstmanufacturedpelleted feed in 1990. In 2001, BangladeshIntegrated Fishery and Poultry Limited” firstintroducedfloatingfeedwhichisverycostly.

According to research reportandvarioussurveysitwasfoundthatthereare100feed-mills inBangladesh thatproduceaquaculturefeedandpoultryfeedtogether.

It is clear that there is no specific studyemphasising sustainability/ feasibility of feed-basedaquaculture,especiallyinBangladesh.

In fact, the production of aqua-feeds hasbeen widely recognised as one of the fast-est expand-ing agriculturalindustries inthe world, withannual growthrates in excessof 30 percentperyear(Tacon,1996). On thebasis of differ-ent categoriesof species, 25percent of totalaqua-feed pro-duction wasfor shrimp andprawn.

The effortshave beenplaced on theuse of by-prod-ucts from themuch larger andfaster-growingterrestrial agri-cultural pro-duction sector,including: 1)terrestrial ani-mal by-productmeals result-ing from theprocessing (i.e.rendering) of

non-food grade livestock by-products; 2)plantoilseedandgrainlegumemeals;3)cerealby-productmeals; and4)miscellaneouspro-tein sources such as single-cell proteins, leafproteinconcentrates,invertebratemeals,etc.

However, the eventual success of thesepotential feed resources as fishmeal replace-ment in aquafeeds will depend upon thefurther development and use of improved

30 | InternatIonal AquAFeed | March-april 2012 March-april 2012 | InternatIonal AquAFeed | 31

FEATURE

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Volume 15 I s sue 2 2 012

the international magazine for the aquaculture feed industry

Filtration in recirculation particle control

Fish Protein Hydrolysates– FPH enhance resistance of aquaculture species to

different types of stress

The quest to keep Salmon in the pink naturally

Aquaculture development in Sub-Saharan Africa

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