Farming freshwater prawns

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thoroughly disinfecting the whole hatchery installation, so it is not a decision to be takenlightly.Another disease which has mainly been noted to affect larvae is known sometimesas the ‘exuvia entrapment disease’ (EED) or as the ‘moult-death syndrome’ (MDS) or as the‘metamorphosis moult mortality syndrome’. The characteristic of this disease is that thelarvae get trapped in the old exoskeleton (exuvia) during moulting. It is mostly noticedtowards the end of the larval rearing cycle, especially at the moult which occurs when stageXI metamorphoses into the PL stage. The mortality rate at this point can be very high. Thecause of EED is not known; it may have multiple causes. It may imply that the diet isnutritionally inadequate and requires enrichment. Difficulties in shedding the oldexoskeleton during moulting have also been observed in juvenile and adult prawns. Themoulting process is stressful and may be difficult for weakened animals, and it is at thistime that hidden problems become noticeable.MONITORING PERFORMANCEMany hatchery operators judge when to make changes in the feeding regime, for example,by the number of days that have elapsed since the larvae were stocked. This is satisfactoryif a larval batch is performing well and you are basing your management on previousexperience. You can judge the progress of your larvae more accurately by stereoscopicmicroscopic examination. You should do this on a daily basis until the first PL appear inthe tank. A key to the various larval stages is provided in Annex 1.You will very quickly become able to gauge whether your larvae are feeding andgrowing well by crude visual examination, using a white sight board (Figure 33) andobserving the behaviour of the larvae. Healthy larvae swarm at the surface of the water(especially in the first 10 days) when the aeration is turned off, feed actively, have a redbrownishpigmentation, and are not observed to cannibalize. Unhealthy larvae accumulateat the bottom of the tank and are often bluish in colour. Food consumption drops and, if theproblem is already severe, you will see dead larvae. Healthy larvae swim tail first, headdown and ventral side up. Metamorphosis to PL is characterized by a radical change inbehaviour and appearance; for the first time the animals resemble miniature adult prawnsand, instead of swimming freely in the water, many crawl or cling to the tank surfaces.The performance of freshwater prawns during the grow-out phase depends on thehistory of the PL or juveniles stocked. It is therefore important, if your hatchery is to establishand maintain a good reputation for high-quality PL, to monitor the condition of youranimals. A new method to score the condition of M. rosenbergii larvae was developed byTayamen & Brown (1999). This is based upon microscopic examination, followed by scoringon a condition index using a numerical scale. Larvae scoring high on this system havebeen demonstrated to show better growth and survival in various Southeast Asian hatcheries.The scoring system is illustrated in Figure 36a and a larval quality record sheet inFigure 36b.Although survival rates of up to 80% between stage I and metamorphosis to PL havebeen claimed by some hatcheries, 40-60% is more normal in practice. The time taken for alarval batch to metamorphose varies according to feeding and environmental conditions,particularly temperature. In a healthy, well-fed batch, which is maintained within the optimumtemperature range, you should expect to see the first few PL between days 16-20after stocking. Most of the larvae should have metamorphosed into PL by days 25-32 at therecommended water temperature of 28-31°C. Some hatchery operators wait for the last fewlarvae to metamorphose before harvesting but it is not usually economic to maintain anybatch longer than 32-35 days (by which time 90-95% metamorphosis should haveFRESHWATER PRAWNS70
FIGURE36aA method of evaluating the quality of Macrobrachium rosenbergiilarvae is illustrated in this diagram** [CRITERIA Nos. 9 AND 10b ARE NOT ILLUSTRATED IN THIS TABLE; SEE FIGURE 36b]SOURCE: TAYAMEN AND BROWN (1999), REPRODUCED WITH PERMISSION FROM BLACKWELL SCIENCECHAPTER 471
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Farming freshwater prawnsA manual f
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The designations employed and the p
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abstractTHE ORIGINAL MANUAL on fres
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table of contentsABSTRACTPREFACEINT
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Feed type 114Measuring feed efficie
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17. Measuring soil pH 10618. Reason
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87. Keeping market-sized prawns ali
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major subject of cultivation becaus
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has little relevance, especially be
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(zoeae) are just under 2 mm long (f
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TABLE1Body segments (somites) in Ma
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Figure 5The major malemorphotypes o
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tions, where a breeding stock of bo
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most hatcheries operated on flow-th
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BOX 1Removal of iron and manganeseW
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TABLE 3Artificial brackishwater (12
Page 33 and 34: TABLE 4Diluting seawater and brine
Page 35 and 36: mentally cultured at up to 10 ppt;
Page 37 and 38: cal quality and its lack of predato
Page 39 and 40: CHOOSING YOUR SITE: SOIL CHARACTERI
Page 41 and 42: such as fertilizers and equipment.
Page 43 and 44: perate (usually originating from st
Page 45 and 46: 3.2 Holding your broodstock in temp
Page 47 and 48: ing system that consists of a 300 L
Page 49 and 50: 4CHAPTERHatchery phaseALL FRESHWATE
Page 51 and 52: SOURCE: HASSANAI KONGKEOand dust. T
Page 53 and 54: FIGURE17This shows the water flow t
Page 55 and 56: Figure 21The water inthese larvalta
Page 57 and 58: FIGURE24Turn-down drains are the be
Page 59 and 60: FIGURE26Installing a ring main air
Page 61 and 62: Figure 28Power supplies arenot alwa
Page 63 and 64: Water dischargeYou should take care
Page 65 and 66: is recommended. The volume of these
Page 67 and 68: then multiply to cope with the nitr
Page 69 and 70: Regular monitoringof larval waterqu
Page 71 and 72: initial stocking rates shown inBox
Page 73 and 74: Recommendations forgood larval wate
Page 75 and 76: FIGURE35Many of the larvae that go
Page 77 and 78: TABLE 8Hatchery feeding scheduleLAR
Page 79 and 80: ing to avoid BSN leaving the tank.
Page 81 and 82: TABLE10The major diseases known to
Page 83: Notes on potential disease problems
Page 87 and 88: occurred). You are therefore recomm
Page 89 and 90: 5CHAPTERPostlarval holdingand nurse
Page 91 and 92: Figure 39Substrates can beused in n
Page 93 and 94: FIGURE41Postlarvae in plastic bags
Page 95 and 96: pH and temperature of the rearing f
Page 97 and 98: It is difficult to recommend exact
Page 99 and 100: 6CHAPTERGrow-out phaseFRESHWATER PR
Page 101 and 102: FIGURE44ponds may become low enough
Page 103 and 104: FIGURE46Pond banks should have the
Page 105 and 106: FIGURE50The dissolved oxygen levels
Page 107 and 108: Figure 53Where thetopography of the
Page 109 and 110: Figure 56The outletstructure,someti
Page 111 and 112: Figure 58This freshwaterprawn pondh
Page 113 and 114: FIGURE59 cont.CROSS SECTIONSOURCE:
Page 115 and 116: Figure 64Long-shaftaeratorin action
Page 117 and 118: there is only a single stocking), t
Page 119 and 120: TABLE16Lime requirements for treati
Page 121 and 122: semi-intensive stocking rates vary
Page 123 and 124: Keeping rootedplants out ofyour pon
Page 125 and 126: advantages obtained in temperate cu
Page 127 and 128: Polyculture of freshwater prawnswit
Page 129 and 130: only increases the availability of
Page 131 and 132: Using water-stable feeds provides y
Page 133 and 134: MEASURING FEED EFFICIENCYYou should
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Example of feeding ratefor freshwat
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allowed to become too low and there
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found to be hosts for the bopyrid i
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Figure 81A large BCMacrobrachiumros
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7CHAPTERHarvesting andpost-harvest
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FIGURE83You can cull-harvest your p
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FIGURE85Larger ponds may also be cu
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Figure 91HarvestingMacrobrachiumros
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(Figure 95). To kill a batch of 50
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described earlier in this manual) a
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Once the prawns arrive at the point
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properly. They should also be displ
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ANNEX 1, Figures 1-12Macrobrachium
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4ANNEXSource, hatching andenrichmen
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The nutritional quality and physica
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decapsulation improves the energy c
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starved versus enriched BSN. Lavens
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1ANNEX 4TABLEDetermining hatching p
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4ANNEX 4TABLE Hydrating and decapsu
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7ANNEX 4TABLE1. Set up the hatching
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grades the particles and washes the
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2. Stock estimation when postlarvae
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animal, particularly within the gil
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ANNEX 7 FIGURE1The size of the mesh
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8ANNEXSize managementAS MENTIONED I
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2. BehaviourThe behavioural charact
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ANNEX 8 FIGURE3Changing the stockin
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ANNEX 8 FIGURE4Orange claw (OC) and
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9ANNEXFarm-made pond feedsTHIS ANNE
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ANNEX 9, Figure 3Farm-made feedsnee
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4ANNEX 9TABLEFarm-made grow-outfeed
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which the requirements are applied.
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Carapace:Caridean:Cephalon:Chela:Ch
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Genital pores:Gill chamber:Greenwat
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Puddling:Rostrum:Salinity:Sequester
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ConversionsTHIS SECTION OF THE ANNE
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Financial considerationsSOME COMMEN
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ReferencesAlston, D.E. & Sampaio, C
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Fujimura, T. & Okamoto, H. 1972. No
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New, M.B., Singholka, S. & Vorasaya
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This new manual, which replaces an
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