40 ... Villalon

Chapter 9

Juvenile Transfers

Scheduled TransfersThere is a great advantage to stocking productionponds by the method of juvenile transfer as comparedto directly stocking postlarvae. The inherent qualitiesof semi-intensive culture strategies make it difficultto estimate actual population numbers and biomassaccurately at any given moment during the culturecycle, but shrimp in the juvenile stages tend to havea better developed immunological response systemand are more resistant to stress; as a result, mortalityrates are significantly reduced. During the first fiveweeks after stocking postlarvae, mortality is gener-ally 25 percent to 35 percent of the originally stockedpopulation. The mortality of juveniles by the timethey reach a target harvest weight of 23 g, on the otherhand, is generally 20 percent to 35 percent over a 25-week culture cycle. Since the mortality curve is ob-viously not linear over the entire cycle from postlarvaeto harvest size, it is advantageous to run the shortereconomical risk of the five-week period in the nurs-ery pond rather than the 25-week period of a relativelylarge production growout pond. The economicalimplications are not only restricted to the investmentof time and production area risks, but also include theequally important management of feed rations dur-ing the entire culture cycle.

It is more economically efficient, in terms of pro-duction forecasting as well as implementation ofmore accurate feed and culture management strate-gies, to use production models such as ponds stockedwith a known number of relatively resistant juvenilesthat reflect a more linear mortality curve over a 25-week period.

Transfer of juveniles into a growout productionpond is the final step involved in "locking in" thegrowout pond into its production forecast for thefinal harvest. Although the farm maintains a currentannual production forecast divided into monthlyintervals, the juvenile status at transfer is the deter-mining factor in the re-evaluation of production es-timates. For this reason it is essential that correcttransfer techniques be implemented so that produc-tion projections may maintain their credibility. Oncethe juveniles are transferred into a growout pond,there is very little that the biologist can do in terms ofpopulation analysis and performance evaluationsuntil the pond is harvested. As a result, every effortshould be made to compile as much accurate data aspossible during the transfer operation in order to beable to make a more precise subjective evaluation oftransfer results to support the growout pond's har-vest forecast.

As described in Chapter 8 under Growth Moni-tori ng, the target weight for juveniles to be transferredis between 0.6 g to 0.8 g. Although in practice, thisweight may be reached within four to five weeks,with postlarvae stocking densities previously men-tioned, the governing criteria determining the transferdate is the average weight of juveniles. Since juvenileshave a tendency to molt at a higher frequency thanadults, it may be necessary to sample the juvenilesmore than once per week to ensure that they do notexceed the narrow weight range optimal for trans-ferring.

Prior to transferring, the degree of carapace hard-ness should be determined to guarantee the maximumprotection of juveniles from possible physical dam-age experienced during transfer.

During sampling, the percentage of juveniles withsoft carapaces should be calculated. If the percentageof juveniles with soft carapaces exceeds 5 percent, thetransfer date should be postponed until this per-centage is under 5 percent.

In summary, there are four major factors to beconsidered in establishing or programming theschedule for transferring juveniles from nursery togrowout pond. These are:1. Average juvenile weight �.6 g to 0.8 g!;2. Degree of carapace hardness <5 percent soft

shell!;3. Adequate preparation of growout pond; and4. Coincidence of transfer with the spring tide phases

of the moon. Although this is not critical, suchtransfers are generally completed more efficientlybecause of increased shrimp activity.If the farm's biological staff has meticulously

prepared and organized the transfer in advance, thejuveniles transferred into the growout pond shouldexperience the compensatory growth response phe-nomena. Although the physiological reason for thisphenomena is not completely understood it is thoughtto be directly related to the positive metabolic effectsof the change in environment experienced by thejuveniles from one of high densities and reducedavailable food, to one of relatively low densities withan increase in available food. This compensatory growthmay also be related to the elimination of growth in-hibiting hormones secreted by the juveniles in a highdensity situation when the maximum capacity of thenursery pond is approached. The compensatory growthphenomena may last from two to three weeks in thegrowout pond without the use of pelleted feeds.

Villalon ... 41

Pond

Harvest Basin�

Drainage CanalFigure14. Schematic diagramof nursery pond harvest basinon effluent weir gate.

Transfer Mechanisms

Juveniles are nocturnal animals and have a naturalmigratory instinct during the spring tides, when themoon phase is either full or new. It is more efficient totake advantage of these inherent qualities and com-mence the transferring of juveniles during the night,when swimming activity is increased. Night trans-fers are also more advantageous in terms of maintain-ing cooler temperatures during the operation.

The gravity harvest method is best, but this maynot always be possible in nursery ponds with inad-equate drainage capabilities. It then becomes neces-sary to seine juveniles or capture them by cast net ting.

The objective of the transfer mechanism is toharvest, quantify, transport and stock juveniles fromthe nursery pond to the designated growout pondwith the minimal amount of stress. The main areas ofpossible stress in normal gravity harvest transfersare:1. The elapsed time juveniles are concentrated in

high density.2. The water current pressure that may cause

physical damage to juveniles by pressing themagainst the harvest box mesh screen.

3. The collection method of juveniles from the har-vest box.

4. The elapsed time animals are out of water duringthe weighing and quantifying of juveniles ex-tracted from the harvest box.

5. The water quality and elapsed time in the trans-port tanks as well as transport time to the growou tpond, and

6. The method of draining water and juveniles fromthe transport tanks to the growout pond.

In those nursery ponds where the bottom topog-raphy does not allow adequate drainage, it is neces-

sary to use seine nets or cast nets. This method may bevery damaging to the juveniles as a result of pullinga net along the pond bottom. This method also requiresthat farm personnel walk in the pond, which resultsin a high degree of sediment suspension that mayfoul gills and cause undue stress to the juveniles. Inthe majority of nurseries where seining becomesnecessary it is recommended that the gravity harvesttechnique be utilized first and that the nursery pondbe refilled to repeat the same procedure several timesbefore terminating the transfer operation with theseine net. This method reduces the number of juve-niles exposed to the high stress and low efficiency ofseine type transfers, and should significantly improvesurvival rates of transferred juveniles.

In the majority of cases, nursery ponds are de-signed to be between 0.60 and 0.80 hectares in surfacearea in square or rectangular shapes. Typical di-mensions are 70 m by 120 m with an average depth of1.4 to 1.6 meters.

The nursery pond bottom topography shouldhave a cross-fall slope of 0.5 to 1 percent for completedrainage capabilities and a minimum water depth atthe inflow dike of 0.8 m. Using this type of nurserypond design, night transfers of more than 1,000,000juveniles can be done in six hours.

Gravity transfer techniqueFigure 14 and Plate 30 show a schematic diagram

of the pond harvest basin concentrating and captur-ing juveniles for transfer.

Transfers should be completed by 0600 hours �a.m.!. This scheduling criteria should be used for twoimportant reasons:1. The light at dawn facilitates visibility in order to

determine if juveniles are burrowing into the

42 ... Villalon

Plate 30. View of nursery pond han>est basin used forcapturing and concentrating j uz>e»iles.

Plate 31. Sixty percent reduction of nursery pond water lez>elprior to commencing juvenile tra»sfer operation.

Plate 32. Wooden framed, small mesh harvest box structurethat stands partially submerged in harvest basi».

mud and are not being efficiently captured, and2. At dawn, the temperature is still cool enough to

finish the transfer, or, if problems arise andcompletion is postponed, early daylight permitsadequate visibility to partially refill the nurseryin an effort to control water temperature.

In the majority of nursery transfers that can becompleted in six to eight hours, the operation shouldcommence between 2200 hours �0 p.m.! and mid-night. If it is estimated to take longer than eight hours,then the schedule should be moved forward earlier!.

Transfers should not be initiated before 1800 hours �

p.m.!, unless the weather is rainy or overcast.Once it has been established that the juveniles are

prepared for transfer and the date has been set, waterlevels in the nursery pond should be lowered by 60percent, the day before the operation. If the nurserypond's water depth at the effluent weir gate is 1.5 m,it should be reduced to 0.6 m before beginning thetransfer Plate 31!.

It is recommended that a screen cleaner be perma-nently placed on the effluent weir gate to ensure thatthe screen does not plug and rupture, as well asensuring that the water pressure against the effluentscreens is not so great as to cause physical damage tojuveniles in the vicinity of the weir. In the latter case,it will be necessary to drain the nursery at a slowerrate or a 6 mm mesh convex net can be temporarilyinstalled just in front of the effluent weir gate todiminish water pressure and crushing of juvenilesagainst exit screens.

The main objective in starting with a 60 percentreduction in nursery pond water depth is to enhancethe capture efficiency. With water levels at themaximum operative level, very few juveniles will becaptured during the first half of the transfer becausethey are dispersed throughout the entire water vol-ume, It becomes necessary to reduce the total volumeof the nursery and slightly concentrate the juvenilestowards the effluent side in order to ensure rapidharvests.

Although juveniles are nocturnal animals, theyare photopositive. A strong, battery-powered, halo-gen lamp with high intensity should be located on topof the effluent weir gate and directed at a 30' angleinto the water surface approximately 3 to 4 metersfrom the entrance area of the effluent weir gate. Thislight serves to attract juveniles towards the effluentgate where the current will carry them out of thenursery and into the harvest box. The effectiveness ofthe light increases as the total volume in the nurseryis reduced.

Plate 32 shows the harvest box structure that is

placed within the harvest basin of the effluent gate.The wooden frame slides into the effluent tunnel

slide channels and is sealed. A fine mesh � mm!cylindrical tunnel connects the wooden frame to theharvest box, which is lined with 2mm mesh. The

Villalon ... 43

Plate 33. Harvest box structure in location within nurserypond harvest basin.

harvest box is submerged within the harvest basin;the walls of the box have sufficient freeboard to keepthe juveniles from jumping out Plate 33!.

The concept of this harvest system takes advan-tage of the benthic behavior of juveniles. Once thejuvenile is in the box, it will find a substrate on whichto attach, either horizontally or vertically. When thejuvenile is on the bottom of the box or attached to thewalls, it is out of the turbulent current of watercoming through the box.

When all equipment is in place, the restrictionboards in the effluent weir should all be removed.Since the harvest is conducted by surface drainage,the restriction boards hamper the easy movement ofwater and juveniles.

Enough down boards should be placed on theback end of the harvest basin to ensure adequatewater depth, both in the harvest basin and harvestbox Plate 34!. Once the nursery begins to drainharvest, the water will spill over the down boards butshould not overflow the harvest box.

Juvenile transfer begins by raising the doubleeffluent filter screens and removing sufficient downboards from the weir gate to allow surface drainage.It is of critical importance to manage the quantity ofwater draining over the effluent down boards prop-erly'since too much water will cause excessiveturbulance and water pressure, resulting in damagedjuveniles. The best results are obtained by limitingthe amount of water over the down boards to 20 cmmaximum Plate 35!. This should result in efficientdrainage and juvenile harvest as well as maintaininga minimal water depth in the effluent gate culvert tunnel! of 10 cm to 15 cm.

It is necessary to maintain 10 cm to 15 cm of waterover the cement floor of the culvert in order to cush-ion the fall of juveniles, otherwise the juveniles maybe physically damaged by the rough surface of theconcrete slab.

Plate 34. Down boards in place on effluent side of nurseryharvest basin to maintain adequate water levels in basin andbox.

Plate 35. Approximately 20 cm of water draining over efflu-ent down boards is alloroed during transfer operation. Thewooden pole and hand show water mark levels.

44 ... Vitlalo»

Plate 36. Dipnets are used to extract juveniles from harvestbox and deposit them in plastic box containers.

Plate37. Waterfrom plasticboxcontainersisallowed todrainwhile debris and predators are eliminated.

Plate 38. Juveniles in plastic box containers being accuratelyweighed.

The attraction exerted by the halogen lamp willcause increased activity of shrimp near the effluentgate, depending on the rate of capture. The harvestbox containing the juveniles should be harvestedevery 15 minutes, or when it contains approximately15 kg of juveniles, whichever comes first.

The juveniles are extracted from the harvest box,using a fine mesh � mm! scissor net or dipnet Plate36!. They are then deposited in the plastic box con-tainers and allowed to drain for approximately 15seconds Plate 37! before weighing Plate 38!. Theplastic box containers should not be filled with morethan 2.5 to 5 kg of juveniles Plate 39!. Care should betaken to avoid their jumping out of the box containers a cover net with elastic edges may be employed tocover the plastic box as it leaves the harvest box untilit is deposited in the hauling tank!.

During the 10 to 15 seconds allowed for adequatewater drainage from the plastic boxes, all trash andpotential predators such as fish and crabs should bemanually removed Plate 40!. This allows for accurateweighing of the quantity of juveniles as well as pro-tecting the future shrimp population in the growoutpond from predators.

At times, it may become necessary to install one ofthe two effluent filter screens, in the event that toomany juveniles are being harvested in relation to theamount that can be carefully and efficiently handledby farm personnel. It is better to install the filterscreen than the down boards, as the back pressurecaused by installing down boards may cause thejuveniles to retreat into the nursery pond.

During the last phases of the transfer harvest,when the water level in the nursery pond is low, thewater current velocity may not be sufficient to drainthe juveniles from the nursery. In this case, it becomesnecessary to implement a more effective means ofattraction strategy. Fresh, clean pond water shouldbe allowed into the draining nursery pond, this freshwater acts as a strong attractant to the remainingjuveniles. In order to implement this strategy effec-tively, it is necessary to insert down boards at the endof the effluent gate culvert and allow water to drainin great quantities from the adjacent nursery pondthrough the "Y"-shaped dual effluent gates. Since theadjacent nursery pond should have significantlyhigher water levels, the water will easily drain fromthe adjacent nursery into the partially harvested one Plate 41!. This fresh water should flush the area nearthe mouth of the effluent weir and allow sufficient

water to cover approximately a 20 m radius with 30cm water depth. The incoming fresh water shouldimprove the water quality in which the juveniles areconcentrated, as well as decrease the density andattract all juveniles in the vicinity to swim toward theeffluent gate.

Once the required amount of water has beenallowed to enter the nursery, the system should be

Vill>zlo» ... 45

Plate 39. 2.5 to 5.0 kgof jzzuer tiles per l>lastic box z or ztairzer.Notice the abser zcz of nrzzt ercess ztz l»is or»rertator s.

Plate 41. Flzzshi ngfresh u ater i» rez>erse throzzgh tlze efflzzentzveir gate to i»rl>zzrve u>nter qu»litzt corzzlitiorzs as u>ell asi> zcrease zvater z>olzzrrre zlzz ri�»g fi r znl trnr zsfz r lrroce>hz>res.

reversed. This is done by damming the effluent floin the adjacent nursery and raising the filter screen inthe effluent of the nursery being transferred. With theincrease in volume of water, effluent water currentvelocity should be significantly increased, which re-sults in a mor» efficient capture/drainage rate tor thcjuveniles. This operation should be repeated a» manytimes as necessary to ensure that no juveniles are leftbehind in the drained nursery because of burrowingaction or stagnated puddle».

If a filled nursery pond doesn't exist next to thenursery being transferred, it may be necessary to usea 15 cm to 20 cm auxiliary pump to transfer waterfrom the effluent canal into the nursery being tran»-ferred Plate 42!. The main objective is to increase thewater volume sufficiently to allow effluent current toincrease and effectively drain juveniles.

Throughout the entire transfer operation, it isnecessary to monitor D.O. and water temperatures

Plate 40. Prrterztini lrrectator» that haz>e bee» remzn>ezt fromplzrstic I>zrn's czrr ztni r >i > zg tire j zzz>z >ziles.

Plnte 42. Flzzslzi»g zvz'th fresh zvntz r u>ith a 20-cm azzrilarz/l»>rr>P tz>ntttzzct juz>elliles a>M i>zcreaseu>ates nolzzrrzedzzrirzg>firznl trzzrzsfi'r lrroce>f»res.

Plnte43. Morzitorirzg>D O. nrzzt zvater te>nperat»reat ngzzlari»terz>nls <t»rirzg tire tra>zsfer olreratiorz.

every two hours Plat« 43!. If D.O. levels drop below3 ppm or watvr temperatures»u rpass 32*C it is nece»-sary to t<ikc vnlergency mca»ure» hv reversing thvdrainage process and e ithvr letting or pumping frv»hclean water into the effluent are<i. Thc opening ofentrance weir gatvs or inflow tube» may bc necessaryto supplement thc entry of fresh water into thc nursvrv.

Seine net transfer techniqueComplete drainage by gravity through thc cfflu-

cnt weir g<itc is not possible for ill nursery ponils. Inthose nurseries where drainage is a problem, it i»necessary to finish thv transfer with a seine net. Mostof the transfer can be performed by gravity <is dc-scrihcd in thc previous svction, thereby causingminimal stress to the m<ijoritv of the juveniles. Thclast phase of the transfer will have to be carried outwith thc svinc net and undvr highvr stress conditions.The unit can he refilled to <i dvpth of30 cm andharve»t by gravity drainagv! can bc attempted oversever<al consecutivv evening» prior to initiation ofseining. Feed can also bc oftcrvd vach morning infront of the effluent gatv toattr<ict animals towardsthe w»ir gate during the two or three day» of repeatedgra vi ty tran» I er.

Th» critical problem in transferring a nursvrypond with nets i» that a r«latively 1<irgc number offarm pvrsonncl i» required to pull thc nvt through thvnursery <it i«<a»t »ix men, d«pending on thv size of thvseine!. This number of people walking through thvpond significantlv affects water quality in <a nvgativvway as a result of th» incre as» in rvsuspendcd bottomsediments.

Sclnlng Is g 'ncr<illy po»tponcil until luvcnllcs arvlarger in average wvight �.0 grams!. This is bcc<au»vsmaller juvenile» of 0.60 gram» v ill «scape throughthe mesh of tile seine nct. Sm,aller mesh size seincs arv

impractical because thvy plug c'a»ily with the bottommud, resulting in a nlud /ju vvnile»lurry that is detri-mental to captured juvenile». In order to rvducc thvamount of mud inside thc seine drag, the mesh sizvshould he no smaller than 0.5 to 1.0 cm square.Juvenile» of 2 g average weight vill be easily capturedand rvlativelv trvv of bottom mud.

Thv seine drags should b» circular in shape andshould bc dragged for relatively short distances lpp.50 m!. Longer drags are detrimental for the juvcnil»»and result in poor performance of ju venilcs in growou Iponds.

During any seine transfer, it is necessary to flushfresh water through thc stagn<ate'd ar«as. This shouldbc done by allowing fresh water to enter through theinflow gates or tubes and letting thv lower qualitvwater in the puddle exit through the effluent gitewithout significantly increasing the water depth inthc area bclng sclnc-harv»»tcd.

After every individual drag of the seine, juvenilesshould he concentrated at the shore. They should hc

washed with watvr from the puddle to elimin<ite anymud debri» and predators such a» fish and crabsbefore tran»ter into plastic boxes used in the quanti-fication operation.

During thc I'inal phase of any transfer, either bygravity harv«st or by seine net, th» critical f<ictorgovvrning the success of the operation, stresswise, isthe quality of w,lt»r in which the juveniles find them-selves in the. nursery. A» mentioned before, D.O. andwater temperatures should be monitored frequently,especially during the list phase. Also of critical im-portance during low witcr depth in the nurse ry is therisk of prcd ation hy <iqu<itic birds. It is vital that therebe personnel armed with shotguns present at dawnon the nursery banks to discourage bird predation.Predatory birds include the cormorant, heron, egretand common seagull. A cormorant may consumehalf it» body we ight pcr day. If thc bird weighs 1.5 kgit could concievahly consume almost O.fl kg of juve-nilv shrimp. It the juvcnilvs weigh 0.6 g each �,700juveniles/kg!, one bird could con»umc almost 1,360juvenile». A» many as 20 birds feasting in onc nurseryh<i» drastic vconomic repercusions. This necessitatesthe implvmcntation of an aggresive predator controlstr<ategy during the final stages of <inv transfer op-eration.

Juvenile transf'er qIIantificationsWhen <a pproximately 5 kg of juveniles h<avv been

«xtract»d from th» harvest box or the seine net, they,lrc deposit»d in a plastic box, and as mentionedbefore, the water i» allowed to drain for 15 seconds.During this short timv, the technical staff shouldobserve tile juveniles in thv box and extract all debrisand pr«dator». Since qu<antification of juveniles isperformed hy weight, the vxccss weight of debris andpredators will distort the real w»ight of juvenilesbeing transferred. In order to man<age a growoutpond economically and,accurately predict productionc»timatc», it i» essential th,lt the Illo»t accurate juve-nilv tran»fcr v, eight measurement b» obtained.

When the majoritv of the water has been allowedto dr<ain out and all debris and prcd<itors have beenrcmovvd, thc pl,l»tic hox containing juveniles shouldbc weigh <d on a dial balance scale Plate 38!. Theweight ot thv plastic box is subtracted and the netweight of thv juveniles is recorded before introduc-ing thc juvenile» into the transportation containers described prvl iously!.

From cvvry >0 kg of juveniles weighed, the tech-nical stat'f should take a relatively small sample inorder to be able to calculate the number of juvenilesper kg I'late 44!.

An exampl«of »ample frequency during an aver-age transfer tollow»:

i.e, � A O.H ha. nursery that contains 1,120,000juveniles wvighing an average of 0.80 gms each, willcontain a biom,l»» ot 896 kg. If weight samples are

Vitlnlo» ... 47

Plate 44. Weiglzi>zg~ si»all, ra>zzlo»z, rq>re»e>itntiz>z sample ofj «z>e>iilis ti»leter>iiiiie»iir»l>er of jiiz>i »iles l>i > kilog~rrzi».Sai>i pl>' size al>proxi»>at> lit 0.25 kilos>»>i»,

extracted and calculated for every 90 kg of transferredjuveniles then a total of 10 weight samples should bctaken during the course of the entire transfer.

Transfer in a properly constructed 0.� ha nurserypond should take bctv een six to 10 hours.

Juvenile transfers are quantified �! by speciesclassification and �! by size classification. I3oth tac-tors are monitored and calculated from the»arnerandom sample.

Culture species segregationPeiiaeii» <>a>»iai>iei is the predominant commer-

cially cultured specie» on the Pacific coast of theAmericas. Peiineiis stillirostri» is of secondary impor-tance as certain viral pathogens preclude their im-portance in the. commercial sector. I'. ocei>le»tali» andP. califor>zie»sis do not adapt well to large scale com-mercial operations and, a» a result, do not make up asignificant part of commercial production.

Although all four species are found in the naturalenvironment and actively compete for space andavailablc feed, P. i>ceiileiitnlis and V. ezzlifor»ie»»isgenerally disappear from the population ~ hcn theyweigh between 11 and 15 g. This natural selectionprocess is not completely understood, although it isstrongly suspected that thc competitive environmentfound in a commercial production pond is morccongenial for I'. oaiiiin»iei and P. »titlin>»tris and,therefore, these are the predominant species harvestedin the classification of 26-30 through 36-40 count size.Using culture strategies of lower stocking densitiesand smaller harvest target sizes, V. occik'»tali» and P.calif>>r»ie>isis have performed rather well and showcommercial feasibility. However, since the majorityof commercial operations are designed for higherstocking densitic» and smaller harvest target size orlower stocking denisites with larger harvest size,these two species are not considered as attractive lorcommercial production.

Veinieii» stitli rostris ad apts well to commercial ponddesign and criteria but is hampered by its vulnerabil-ity to the IHHN virus. This viral pathogen can com-pletely wipe out the population at the juvenile as ~ ellas the postlarval stages in production hatcheries.

Unless P. »tztlirostris utilized in commercial op-eration» can be guaranteed to be virus-free, survivalin nursery and growout ponds will be, at best, in-consistent and unpredictable.

There has been limited success in many com-mercial operations with mixed stocking stratcgie» ofN! percent P. z>niiiia»iei and 20 percent P. »titlirostris.Thi» strategy is generally employed where there is arelativclv short supply of P. <>aiiiin»iei and an abun-dant supply of V. »titlirost>i». In this particular case,the operator assumes the probable risk of losing 20percent of the P. »t«lirostris forecasted, but is rela-tively sure of maintaining thc majority of the P.z aiiiia»iei population for harvest.

As mentioned above, the majority of commercialfacilitie» choose to produce P. i>a»»a»zzi for its com-mercial adaptability and survival performance. Al-though V. <>aii>ia»iei is specifically vulnerable to theHzzez iili>z i riis l>i iiaei B.P. virus!, it can be screened forthis virus with wet squash mounts under light mi-croscopy. This results in relatively viral-free P.zniiiia»i<i postlarvae if this screening technique. isutilized in commercial hatcheries. IHHN, on the otherhand, i» somewhat morc difficult to screen for.

During the juvenile transfer process, the numberof P, z>n>i»ii»iei juveniles transferred must bc calcu-lated. Thc other secondary species transferred intothe growout pond are not considered in the exercise~>f production torecasting or harvest estimates, butmust bc considered for overall pond management»trategics in terms of culture densities, feed rates andsvater management.

It is important to understand that P. z>a>i>ia»i>i i»the predominant species and the number of V.z>aiiiiniiii'i juvenile» transferred will be used as thebasis for the production harvest estimates, however,management strategies implemented during thcculture cycle may be influenced by the total biomassof all four species of shrimp.

For every 90 kg of juveniles transferred, it iszzeccs»ary to extract a random sample of approxi-rnatcly 0.25 kg to be classified by species and inde-pendently by weight. In theory, for transferral of <znynursery that contains juveniles with an average weightof 0.� grams, a 0.25 kg random sample will containapproximately '310 juveniles that must be segregatedby»pccies. Once the juvenile» are segregated andcounted by individual species, the respective per-centage of each species can be calculated.

There are a variety of methods utilized for idcnti-tying the different species. Aside from body andantenn<ze coloration, the most practical method is bythe rostrum shape and configuration.