PAUL V. ZIMBA. Abstract

Transcription

1 JOURNAL OF THE WORLD AQUACULTURE SOCIETY Vol. 38, No. 3 Septemer, 2007 Effects of Two Densities of Cged Monosex Nile Tilpi, Oreochromis niloticus, on Wter Qulity, Phytoplnkton Popultions, nd Production When Polycultured with Mcrorchium rosenergii in Temperte Ponds JASON J. DANAHER 1,JAMES H. TIDWELL, SHAWN D. COYLE, AND SIDDHARTHA DASGUPTA Aquculture Reserch Center, Kentucky Stte University, Frnkfort, Kentucky USA PAUL V. ZIMBA Ctfish Genetics Reserch Unit, United Sttes Deprtment Of Agriculture Agriculturl Reserch Service, Stoneville, Mississippi USA Astrct The effects of different densities of cged Nile tilpi, Oreochromis niloticus, on wter qulity, phytoplnkton popultions, prwn, nd totl pond production were evluted in freshwter prwn, Mcrorchium rosenergii, production ponds. The experiment consisted of three tretments with three 0.04-h replictes ech. All ponds were stocked with grded, nursed juvenile prwn ( g) t 69,000/h. Control (CTL) ponds contined only prwns. Low-density polyculture (LDP) ponds lso contined two cges (1 m 3 ; 100 fish/cge) of monosex mle tilpi ( g), nd high-density polyculture (HDP) ponds hd four cges. Totl culture period ws 106 d for tilpi nd 114 d for prwn. Overll men fternoon ph level ws significntly lower (P # 0.05) in polyculture ponds thn in CTL ponds ut did not differ (P. 0.05) etween LDP nd HDP. Phytoplnkton iovolume ws reduced in polyculture tretments. Tilpi in the LDP tretment hd significntly higher (P # 0.05) hrvest weights thn in the HDP tretment. Prwn weights were higher (P # 0.05) in polyculture thn prwn monoculture. These dt indicte tht cged tilpi/freshwter prwn polyculture system my provide ph control while mximizing pond resources in temperte res. Mnging stle phytoplnkton popultions is mjor chllenge in erthen pond quculture, especilly if the cultured species does not grze phytoplnkton directly (Hepher et l. 1989). Dense phytoplnkton looms with high photosynthetic rtes cn result in elevted ph levels (.10.0) in the fternoon, cusing physicl nd physiologicl stress (Boyd nd Tucker 1998) nd even prwn mortlity (Strus et l. 1991). Methods used to control high ph hve included lgicides (Osunde et l. 2003), chemicl intervention with cids or uffers (Boyd et l. 1978; Pote et l. 1990), wter exchnge (McGee nd Boyd 1983), nd mechnicl stirring (Perl nd Tucker 1995; Tucker nd Steey 1995). However, ech of these methods hs serious risks or prcticl limittions. Algicides my 1 Corresponding uthor: University of the Virgin Islnds, Agriculture Experimentl Sttion, RR 1 Box 10,000, Kingshill, United Sttes Virgin Islnds USA. Phone (340) ; jdnhe@uvi.edu e toxic (Osunde et l. 2003), flushing is commercilly imprcticl, nd uffers or cids temporrily ddress the symptoms ut not the ctul prolem. Biologicl controls hve shown the potentil to e oth highly selective (Morirty nd Morirty 1973; Dtt nd Jn 1998; Turker et l. 2003) nd cost-effective (Perschcher 1995). Nile tilpi, Oreochromis niloticus, hve the ility to filter-feed on phytoplnkton (Perschcher nd Lorio 1993; Turker et l. 2003, 2003) nd, concomitntly, produce second crop of mrketle niml in polyculture systems (Dos Sntos nd Vlenti 2002). Tilpi nd freshwter prwn hve een shown to e good complimentry species (Brick nd Stickney 1979; Rouse nd Stickney 1982; Meriwether et l. 1984; Rouse et l. 1987; Grci-Perez nd Alston 2000; Dos Sntos nd Vlenti 2002). Grci-Perez et l. (2000) reported tht polyculture of free-swimming tilpi in prwn Ó Copyright y the World Aquculture Society

2 368 DANAHER ET AL. ponds incresed economic returns y 21%. However, when tilpi re unconfined, there is the potentil of negtive species interction including competition over food, unintended nd uncontrolled reproduction y tilpi, nd the need to mnully seprte the two species t hrvest. These negtive fctors cn e eliminted y confining the tilpi in cges (Pgn-Font 1975; Guerrero 1982; Petersen 1982; Rouse nd Stickney 1982; Heinen et l. 1987; Grci- Perez nd Alston 2000). Tidwell et l. (2000) reported tht polyculture of prwn nd tilpi in cges incresed totl pond productivity y 81%. However, cge confinement might reduce the ility of tilpi to efficiently hrvest phytoplnkton for ph control. Some studies hve indicted tht confined tilpi my still e effective iologicl controls ut tht their ility to control lge my e density dependent. Dunseth (1977) reported tht tilpi stocked t pond surfce re of 0.25/m 2 did not ffect lge popultions when compred with ponds without tilpi. However, Perschcher nd Lorio (1993) found tht cged Nile tilpi provided control over phytoplnkton popultions in chnnel ctfish, Ictlurus puncttus, production ponds when stocked t surfce densities of 0.5/m 2. Wng et l. (1998) showed tht tilpi stocked in net pens t 0.32/m 2 improved wter qulity nd incresed shrimp, Peneus chinensis, yields. Tilpi polyculture hs the potentil of improving wter qulity in prwn ponds nd to increse profits through improved prwn yields nd incresed totl pond production (prwn + tilpi). However, to dte most prwn nd tilpi polyculture reserch hs een conducted t firly extensive stocking rtes nd under tropicl or sutropicl conditions. In temperte climtes, more intensive prwn production technologies hve een developed to compenste for the shorter, temperture-restricted growing seson (Tidwell et l. 2000, 2002, 2004). Also, phytoplnkton tx my differ under temperte conditions. The impcts nd fesiility of prwn nd tilpi polyculture need to e evluted under temperte conditions with n revited growing seson ( d). The ojective of this study ws to evlute the effect of two densities of cge-confined tilpi on wter qulity vriles, specificlly ph, in prwn production ponds nd determine the effects on phytoplnkton popultions, prwn production, prwn popultion structure, nd tilpi growth nd survivl. Mterils nd Methods Experimentl System The experiment ws crried out in nine h erthen, rectngulr ponds (1.5-m depth) locted t the Aquculture Reserch Center, Kentucky Stte University (KSU), Frnkfort, Kentucky, USA. Ponds were drined nd llowed to dry 4 wk prior to stocking. Verticlly oriented polyethylene construction/sfety fence pnels mesuring 120 cm wide with mesh size of cm were suspended from metl fence posts to increse ville surfce re y 50% (Tidwell et l. 2000). On My 20, 2003, wter from reservoir ws pssed through 1000-mm filter sock to fill ech pond to depth of 0.50 m. All ponds were treted with 22.4 kg/h CuSO 4 to kill filmentous lge. On 23 My, 7.5 L/h of liquid fertilizer (NPK, 0:45:0) ws dded long with 45.0 kg/h of dried distiller s grins to initite phytoplnkton loom. Wter ws dded to chieve depth of 1.5 m nd mintined t this level for the durtion of the experiment. The experiment consisted of three tretments with three replictes ech. Tretments were s follows: prwn monoculture (control; CTL), prwn/low-density tilpi polyculture (LDP), nd prwn/high-density tilpi polyculture (HDP). The LDP contined two cges of tilpi nd the HDP four cges of tilpi with totl of 100 fish/cge, respectively. All ponds were equipped with 0.5-horsepower ertor (Airoltor, Knss City, MO, USA) modified with deep-drw tue operted nightly ( h) to erte nd prevent strtifiction (Tidwell et l. 2002) nd 0.5-horsepower circultor tht ws operted during the dy ( h). The circultor consisted of n ertor motor mounted horizontlly t depth of 0.5 m. The use of circultors ws discontinued on 5 August sed on undesirle wter qulity from ioturtion of pond sediments.

3 POLYCULTURE OF CAGED NILE TILAPIA AND PRAWN 369 Wter Qulity Dissolved oxygen (DO) concentrtions in ll ponds were monitored twice dily (0800 nd 1600 h) using YSI Model 85 meter (Yellow Springs Instruments, Yellow Springs, OH, USA). Surfce nd ottom pond ph nd temperture for ll ponds were monitored twice dily (0800 nd 1600 h) using YSI Model 60 meter. Totl mmoni-nitrogen (TAN) nd nitritenitrogen were monitored three times per week using n HACH DR/2500 spectrophotometer (Hch Compny, Lovelnd, CO, USA). Unionized mmoni-nitrogen ws clculted from TAN, nd fternoon pond temperture nd ph vlues were recorded for the pond tht dy (Boyd 1990). Alklinity, totl hrdness, nd clcium hrdness were monitored once weekly ccording to procedures for n HACH FF-2 test kit. Alge A chlorophyll- smple ws otined from ech pond monthly using procedures outlined y the HACH chlorophyll- field test kit nd nlyzed using DU 640 UV/Visul spectrophotometer (Beckmn Coulter Inc., Fullerton, CA, USA). A 1-L Kemmerer ottle ws used to smple two different loctions in ech pond t depth of 30 cm every 2 wk for phytoplnkton. The susmples were pooled nd 22-mL liquot of the wter smple ws preserved with 3% formlin nd refrigerted until nlysis. An inverted microscope ws used for phytoplnkton cell counts using strtified counting procedure (Venrick 1978). Smples were enumerted t 5603 nd 1403 mgnifiction using the Utermöhl (1958) technique. Frequently encountered smller forms were identified t 5603, in 10 or more rndom fields, nd rrer lrger forms were identified using 1403 scn of the entire chmer. Prescott (1951) nd Angnostidis nd Komrek (1988) were used s txonomic keys nd to group phytoplnkton y txonomic division for dt nlyses. Phytoplnktons were ctegorized into six groups: chlorophytes or green lge, cynoprokryot or lue-green lge, cillriphytes or ditoms, flgelltes, euglenoids, nd dinoflgelltes. Percent contriutions of ech, sed on cell counts, were rcsine trnsformed prior to nlysis. Results were nlyzed using ANOVA to determine differences etween tretments nd presented in their non-rcsine-trnsformed stte to fcilitte interprettion. Biovolume of frequently encountered species ws clculted ccording to Hillerrnd et l. (1999) for those dtes on which differences in percent contriution of lgl divisions were found. Conversion to iovolume equivlents ffords more relistic comprison of iomss present given the four orders of mgnitude difference in cell size. Tilpi Sex-reversed mle Nile tilpi, O. niloticus, were shipped y truck from commercil htchery (Southern Frm Tilpi, Louisurg, NC, USA) nd received on My 27, They were mintined in four 2450-L flow-through rcewys until pond stocking. On 29 My, tilpi were grded using #62 nd #74 grder rs to remove the lrgest nd smllest of the popultion. Fish retined from the grded popultion were used for stocking. A susmple of 300 individuls were nesthetized with 25 mg/l clove oil nd individully weighed ( g) using n Ohus Scout II scle (Ohus Corp., Florhm Prk, NJ, USA); totl length ws lso mesured ( cm). On 30 My, tilpi were counted nd weighed into groups of 25 fish (Dorn 8000 XL scle; Perkins Scle Corp., Lexington, KY, USA) nd stocked in rottion until ech cge chieved density of 100 fish/cge. Cges were 1-m 3 round cges constructed of 1.75-mm plstic mesh. On 2 June, tilpi were dignosed with the fungl disese Sprolegni spp. Fish were removed from their respective cges where they were given 1-h th tretment of KMnO 4 t 4 mg/l nd then plced ck into their ssigned cges. For the following 8 d, ded fish were removed nd recorded. The Sprolegni spp. outrek cesed s morning wter temperture rose ove 21 C. Recorded mortlities were replced on 10 June with fish remining from the initil cge stocking. Tilpi were fed n extruded diet contining 32% protein (Rngen Inc., Buhl, ID, USA) to pprent stition once dily in the fternoon ( h). Every 3 wk, tilpi (N $ 10) were dip netted

4 370 DANAHER ET AL. from ech cge, individul lengths nd weights determined nd recorded, nd fish returned to their respective cges. The culture period for tilpi ws 106 d. On 12 Septemer, individul tilpi cges were hrvested. A finl count ws conducted to determine survivl, nd ulk weight ws recorded for ech cge to determine finl verge weight nd production. A rndom smple of three individuls from ech cge ws processed to determine dress-out percentges. Prwn Postlrvl (PL) prwns, Mcrorchium rosenergii, were shipped y ir from commercil htchery (Aquculture of Texs, Wetherford, TX, USA) nd nursed in greenhouse t KSU for 60 d. PLs were held in 3680-L tnks with horizontl sustrte nd fed 40% protein slmonid diet (Rngen Inc.) sed on percent ody weight ech dy, nd wter qulity ws monitored. On 3 June, juvenile prwn were size grded using #14 grder r, nd those retined (top grde) were used for stocking purposes. Individul weights of 400 prwns were determined to estlish n initil stocking weight ( g) using n Ohus electronic lnce. Juveniles were hnd counted into groups of 100 nd stocked in rottion etween ponds until the desired pond stocking density of 69,160/h ws chieved in ech pond. Prwn were fed one-hlf the dily rtion twice dily (0900 nd 1400 h) using sinking 32% protein prwn diet (Frmer s Feed, Lexington, KY, USA) distriuted evenly cross the pond surfce. Prwn feeding ws sed on schedule from Coyle et l. (2003). Prwn were smpled (N $ 30) every 3 wk to determine verge weights. The culture period for prwn ws 114 d. On 23 Septemer, wter levels in ech pond were lowered to 0.5 m. On 24 Septemer, sustrtes were removed nd ech pond ws seined t lest three times. Remining wter ws drined nd remining prwns were hrvested y hnd. Prwns were rinsed in clen wter, nd then, ulk weight nd totl count were recorded to determine finl production, verge weight, nd survivl y pond. Rndom smples of $300 individuls from ech pond were individully weighed nd ctegorized into their respective sexul morphotypes (Tidwell et l. 1999) Economics Economic nlyses for prwn monoculture nd prwn/tilpi polyculture were clculted using the enterprise udget method. Fixed costs were sed on the initil ssumption of hypotheticl frm with single 0.4-h pond. This model ws directly dopted from the smll-scle Kentucky quculture frm model proposed in Dsgupt nd Tidwell (2003). Hence, the totl nnul fixed cost ws $ for monoculture, $ for LDP, nd $ for HDP, which ccounts for the tilpi cges (cge cost 5 $35.90/cge, life spn 5 5 yr) nd power tke-off trctor (PTO)-powered ertor (cost 5 $500, life spn 55 yr) used in the HDP tretment only. Operting costs nd output prices were dopted from Dsgupt nd Tidwell (2003) nd modified to include the dditionl expense of stocking nd feeding tilpi nd the extr fuel cost nd mintennce ssocited with the PTO ertor. Feed prices were ssumed to e $396/ mt nd $484/mt for prwn nd tilpi diets, respectively. Juvenile prices were t $0.08/hed nd $1.00/hed for prwn nd tilpi, respectively. Output prices were kept t $12.10/kg nd $4.40/kg for prwn nd tilpi, respectively. Sttisticl Anlysis A one-wy ANOVA nlysis ws used to compre wter qulity nd prwn hrvest dt etween tretments. If differences were identified s significnt y ANOVA (P # 0.05), mens were seprted using the lest significnt difference test (Zr 1984). An ANOVA ws used to determine if chlorophyll- dt were different etween tretments. For nlysis of lge undnce nd iovolume, differences were considered significnt t P # This higher level of significnce ws chosen in light of the multiplictive errors of time, smple size, counting method, iovolume conversion, nd Type 1 error. A two-smple t-test ws used to compre iovolume mesurements etween the HDP nd the CTL tretments only. A two-smple t-test

5 POLYCULTURE OF CAGED NILE TILAPIA AND PRAWN 371 ws used to compre tilpi hrvest dt etween polyculture tretments. Feed conversion rtio (FCR) ws clculted s follows: FCR 5 feed fed/weight gin (Tidwell et l. 1999) sed on the mount of sinking diet for the prwn nd floting diet for the tilpi. Specific growth rte (SGR) ws clculted s follows: SGR (%/d) 5 ([(ln W f ln W i )/T] 3 100), where W f is the finl weight, W i the initil weight, nd T the totl dys of the study (Wester et l. 2000). Production size index (PSI) ws clculted s follows: production (kg/h) 3 verge weight (g) O 1000 (Tidwell et l. 2000). Results Wter Qulity There ws no significnt difference (P. 0.05) etween tretments in overll mens for temperture, unionized mmoni-nitrogen, chlorophyll-, lklinity, totl hrdness, or clcium hrdness (Tle 1). There were no significnt differences (P. 0.05) in morning DO concentrtions etween tretments (6.5 mg/l, overll). However, fternoon DO concentrtions in the CTL ponds (8.4 mg/l) were significntly higher (P # 0.05) thn in either polyculture tretment, with the concentrtion in the LDP tretment (7.7 mg/l) significntly higher (P # 0.05) thn in the HDP tretment (7.4 mg/l). Significnt differences (P # 0.05) for monthly fternoon DO concentrtions re shown in Fig. 1. Over the durtion of the study, overll mens for surfce morning ph vlues were significntly higher (P # 0.05) in CTL ponds (7.9) thn in polyculture ponds (7.8), s were fternoon surfce mens (8.3 nd 8.2, respectively). Overll mens for fternoon ottom ph were gin significntly higher (P # 0.05) in CTL ponds (8.3) thn in polyculture ponds (8.0), while differences etween LDP nd HDP tretments were not significntly different (P. 0.05). Monthly mens for ottom ph levels in the fternoon (the most criticl points) re shown in Fig. 2. There ws no significnt difference (P. 0.05) in overll TAN concentrtions etween polyculture tretments (1.0 mg/l), ut these were significntly greter (P # 0.05) thn concentrtions in monoculture CTL ponds (0.7 mg/l). Monthly TAN concentrtions etween tretments re shown in Fig. 3. Overll nitrite-nitrogen TABLE 1. Tretment men of wter qulity prmeters smpled in the 114-d experiment. Tretment Vrile Control Low-density polyculture High-density polyculture Temperture (C) 25.9 ± ± ± 0.3 Oxygen (mg/l) Morning 6.8 ± ± ± 0.5 Afternoon 8.4 ± ± ± 0.1 c ph Morning Surfce 7.9 ± ± ± 0.0 Bottom 7.9 ± ± ± 0.1 Afternoon Surfce 8.3 ± ± ± 0.1 Bottom 8.3 ± ± ± 0.1 TAN (mg/l) 0.7 ± ± ± 0.0 Unionized mmoni (mg/l) 0.1 ± ± ± 0.0 Nitrite-nitrogen (mg/l) 0.1 ± 0.0 c 0.2 ± ± 0.0 Chlorophyll- (mg/l) 13.4 ± ± ± 13.1 Alklinity (mg/l) 85.4 ± ± ± 4.7 Hrdness (mg/l) ± ± ± 1.9 Clcium hrdness (mg/l) 94.4 ± ± ± 1.9 TAN, totl mmoni-nitrogen. Tretment mens within row followed y different superscripts re significntly different (P # 0.05) y ANOVA.

6 372 DANAHER ET AL. mg/l Control Low-Density Polyculture High-Density Polyculture June July August Septemer Month FIGURE 1. Monthly mens for fternoon oxygen concentrtions for ech tretment. Different letters indicte significnt differences (P # 0.05). concentrtions followed grdient, with the concentrtion in the HDP tretment (0.2 mg/l) significntly higher (P # 0.05) thn in the LDP tretment (0.2 mg/l), which ws significntly higher (P # 0.05) thn in the CTL ponds (0.1 mg/l). Eighty-two gener of phytoplnkton, from six lgl divisions, were identified during the experiment. Chlorophytes, cillriophytes, nd cynoprokryot dominted in terms of numeric counts nd species diversity. Other lgl divisions identified included cryptophytes, euglenoids, nd dinoflgelltes. The green lge, Scenedesmus spp., dominted in terms of lge undnce nd numer of identified species. The most common cynoprokryophyt oserved during the experiment were Aphnocps delictissim, Dctylococcopsis rhphidiodes, Microcystis eruginos, nd Plnktothrix sp. The most frequently encountered gener in CTL ponds ws the chlorophyte Scenedesmus qudricud vr. mxim nd the cynoprokryot Plnktothrix sp., found in 50% or more of the phytoplnkton smples. In the LDP nd 8.50 ph 8.00 Control Low-Density Polyculture High-Density Polyculture 7.50 June July August Septemer Dte FIGURE 2. Monthly mens for fternoon ph smpled t pond ottom for ech tretment. Different letters indicte significnt differences (P # 0.05).

7 POLYCULTURE OF CAGED NILE TILAPIA AND PRAWN 373 mg/l Unionized-Ammoni-Nitrogen Control Low-Density Polyculture High-Density Totl Ammoni-Nitrogen Control Low-Density Polyculture High-Density 0 June July August Septemer Month FIGURE 3. Monthly mens for totl mmoni-nitrogen nd unionized mmoni-nitrogen concentrtions for ech tretment. Different letters indicte significnt differences (P # 0.05). HDP tretments, D. rphioides nd Scenedesmus spp. were the most frequently encountered gener (found in 50% or more of the phytoplnkton smples). There ws no significnt difference etween tretments (P. 0.10) in dinoflgellte undnce. On smpling dtes 6 June, 20 June, 24 August, nd 9 Septemer, there were no significnt differences (P. 0.10) etween tretments in terms of percent contriution of ech lge group. However, t the 7 August smpling, ponds without tilpi hd significntly lower percentge (P # 0.10) of chlorophytes (Fig. 4) nd significntly higher percentge (P # 0.10) of cynoprokryophyt thn the polyculture tretments, ut no significnt differences (P. 0.10) etween polyculture tretments for chlorophytes or cynoprokryophyt. On smple dtes 8 July nd 24 July, ponds without tilpi hd greter numer (P # 0.10) of cillriophytes thn the HDP (Fig. 4); however, there ws no significnt difference (P. 0.10) etween the polyculture tretments. On dtes when percent contriution of lgl divisions were significntly different (P # 0.10), iovolume ws clculted for frequently encountered species in the CTL nd HDP tretments (Tle 2). As result of low occurrence of the flgelltes nd euglenoids, further nlyses were not done on these groups. Prwn Averge hrvest weights of prwn in the polyculture tretments (43.2 g) were significntly greter (P # 0.05) thn in the prwn monoculture tretment (36.4 g), ut not significntly different (P. 0.05) from ech other (Tle 3). Prwn production in the HDP (2720 kg/h) ws significntly greter thn (P # 0.01) in the LDP tretment (2368 kg/h), which ws greter thn (P # 0.01) in the CTL ponds (2125 kg/h). There were no significnt differences (P. 0.05) in survivl mong prwns in the three tretments, which verged 85% overll. The prwn FCR in the HDP (1.9) ws significntly lower thn (P # 0.01) in the LDP (2.2), which ws lower thn (P # 0.01) in the CTL (2.4). The SGR (g/d) for prwns in oth polyculture tretments (0.37 g) were significntly higher (P # 0.05) thn in CTL ponds (0.31 g). The PSI ws not significntly different (P. 0.05) etween polyculture tretments (123), ut oth were significntly higher thn (P # 0.05) in CTL ponds (79). There ws no significnt difference (P. 0.05) in the percent mrketle prwns ($ 20 g) etween tretments, with n overll verge of 93.3%; however, oth polyculture tretments hd significntly higher percentge (P # 0.05) of premium prwns ($ 30 g) (83.0%) thn CTL ponds (70.4%).

8 374 DANAHER ET AL. Percentge (%) Chlorophytes Percentge (%) Cynophytes Percentge (%) Ditoms Percentge (%) Dinoflgelltes Control Low-Density Polyculture High-Density Polyculture 6/6 6/20 7/4 7/18 8/1 8/15 8/29 Dte FIGURE 4. Percent distriution of lgl groups on individul smpling dtes. Tretment mens designted y different letter re significntly different (P # 0.05) using n ANOVA. The rrow indictes when the circultors were discontinued in ll experimentl ponds. Totl prwn yields incresed 12% in the LDP nd 28% in the HDP, compred with the CTL. The three tretments hd no significnt impct (P. 0.05) on prwn popultion structure in terms of numers of ech sexul morphotype (nlyzed s percentge of sex) (Tle 4). The verge weight of lue clw mles (BC) ws significntly greter (P # 0.05) in the HDP (71.9 g), nd the verge weight in the LDP tretment (66.7 g) ws significntly higher

9 POLYCULTURE OF CAGED NILE TILAPIA AND PRAWN 375 TABLE 2. Direct comprison of men iovolumes (mm 3 /ml) of lgl tx in production ponds for dtes when differences in lgl undnce occurred. 1 Dte Vrile Tretment Aulcoseir grnulte vr. ngustissim Species Scenedesmus qudricud vr. mxim Dctylococcopsis rhphidiodes Septemer 8 Control ± High-density polyculture ± Septemer 24 Control ± High-density polyculture ± August 7 Control ± ± 72.9 High-density polyculture ± ± Thosetxmenson thesmesmple dtefollowed ydifferent superscript re significntly different (P # 0.10) y t-tests. (P # 0.05) thn in the CTL (52.7 g) (Tle 5). There ws no significnt difference (P. 0.05) in verge weight of ornge clw mles (OC) etween polyculture tretments (51.5 g); however, oth polyculture tretments hd significntly higher (P # 0.05) weight thn the CTL (44.0 g). There ws no significnt difference (P. 0.05) mong tretments in men weight of smll mles (SM). The verge weight of reproductive femles (RF) ws not significntly different (P. 0.05) etween polyculture tretments (38.8 g), ut oth were significntly higher thn (P # 0.05) in ponds without tilpi (32.7 g). The verge weight of virgin femles (VF) ws not significntly different (P. 0.05) etween polyculture tretments (29.5 g), ut oth were significntly higher (P # 0.05) thn in ponds without tilpi (26.0 g). Tilpi The verge hrvest weight of tilpi in the LDP tretment (853 6 g) ws significntly higher (P # 0.05) thn in the HDP tretment (810.5 g) (Tle 6). Tilpi density did not ffect (P. 0.05) tilpi survivl (96%, overll) or FCR (1.5, overll) in polyculture tretments. The totl dily feeding rte for prwn nd tilpi reched 67, 142, nd 204 kg/h/d in the CTL, LDP, nd HDP, respectively. The LDP tretment resulted in significntly higher (P # 0.05) SGR (7.0 g/d) thn the HDP tretment (6.6 g/d). At hrvest, there were no significnt differences etween tretments in terms of percent dress out of whole dressed fish (68%) or fillets (40%). Economic Anlysis Tle 7 reports totl revenue, opertionl costs, fixed costs, nd totl profit for the three TABLE 3. Prwn result men (6SD) hrvest weight, production, survivl, FCR, SGR, PSI, percent mrketle prwn, nd percent premium prwn cultured in ponds with nd without tilpi. 1 Tretment Vrile Control Low-density polyculture High-density polyculture Hrvest weight (g) 36.4 ± ± ± 1.5 Production (kg/h) 2,124.5 ± 68.0 c 2,368.3 ± ,720.4 ± Survivl (%) 84.6 ± ± ± 2.8 FCR 2.4 ± ± ± 0.1 c SGR (g/d) 0.3 ± ± ± 0.0 SGR (%/d) 3.2 ± ± ± 0.0 PSI 78.7 ± ± ± 7.5 % Mrketle (.20 g) 93.7 ± ± ± 1.3 % Premium (.30 g) 70.4 ± ± ± 3.4 FCR 5 food conversion rtio; PSI 5 production size index; SGR 5 stndrd growth rte. 1 Tretment mens within row followed y different superscript re significntly different (P # 0.05) y ANOVA.

10 376 DANAHER ET AL. TABLE 4. Men (6SD) numer of prwns clssified into one of five sexul morphotypes t hrvest. 1 Tretment Control Low-density polyculture High-density polyculture Blue clw mles 11.5 ± ± ± 3.1 Ornge clw mles 77.0 ± ± ± 3.1 Smll mles 11.5 ± ± ± 1.6 Reproductive femles 84.2 ± ± ± 9.1 Virgin femles 15.8 ± ± ± Mens within row followed y different superscript re significntly different (P # 0.05). TABLE 5. Men (6SD) weight of prwns clssified into one of five sexul morphotypes t hrvest. 1 Tretment Control Low-density polyculture High-density polyculture Blue clw mles 52.7 ± 1.7 c 66.7 ± ± 3.5 Ornge clw mles 44.0 ± ± ± 1.5 Smll mles 10.5 ± ± ± 1.6 Reproductive femles 32.7 ± ± ± 1.0 Virgin femles 26.0 ± ± ± Mens within row followed y different superscript re significntly different (P # 0.05). technologies. Totl revenue for the CTL, LDP, nd HDP tretments were $10,433.14, $18,864.99, nd $27,210.65, respectively. Totl vrile costs for the CTL, LDP, nd HDP tretments were $ , $10,504.33, nd $14,906.51, with fixed costs totling $ , $ , nd $ , respectively. Profit ssocited with ech technology incresed s TABLE 6. Tilpi results men (6SD) hrvest weight, production, survivl, FCR, SGR, nd percent dress out of cged tilpi cultured in freshwter prwn ponds. 1 Tretment Vrile Low-density polyculture High-density polyculture Hrvest weight (g) ± ± 37.3 Production (kg/h) ± ± Survivl (%) 95.3 ± ± 0.8 FCR 1.5 ± ± 0.1 SGR (g/d) 7.0 ± ± 0.4 SGR (%/d) 1.9 ± ± 0.0 Whole dressed (%) 68.5 ± ± 0.1 Fillet (%) 39.5 ± ± 0.0 FCR 5 food conversion rtio; SGR 5 stndrd growth rte. 1 Tretment mens within row followed y different superscript re significntly different (P # 0.05) using two-smple t-test. production intensified with the CTL erning $ , LDP erning $ , nd the HDP erning $ per 0.4-h pond. The three technologies differed primrily in the stocking costs, feed costs, nd fixed costs. Stocking costs were noticely higher thn the feed costs for ll technologies. Besides the dditionl stocking nd feeding costs ssocited with polyculture, the LDP required the ddition of twenty 1-m 3 cges nd 300% increse in the quntity of ice needed t hrvest. The HDP tretment required forty cges, 493% increse in the quntity of ice, PTO ertor for emergency ertion, nd the dditionl fuel. Discussion Wter Qulity The presence of cged tilpi stocked t rtes $ 5000 fish/h resulted in lower fternoon ottom ph levels in polyculture tretments. However, the ctul rnges of ph were reltively smll. These reserch ponds were lrgely dominted y chlorophytes through the production period. Cynoprokryophyt-dominted

11 POLYCULTURE OF CAGED NILE TILAPIA AND PRAWN 377 TABLE 7. Annul costs nd profit for prwn monoculture nd polyculture in 0.4-h pond. 1 Item (unit) Vlue, $/unit Quntity Control Vlue, $/pond Quntity Low-density polyculture Vlue, $/pond High-density polyculture Quntity Vlue, $/pond Yield (kg) Prwn , , , Tilpi , Totl revenue 10, , , Vrile costs Juveniles (ech) , , , Fingerlings (ech) Prwn feed (mt) Fingerling feed (mt) Chemicls Wter qulity regents (refill) Electricity (kwh) Pumping costs/fuel (no. of times) Lor nd mngement (h) Accounting/legl fees ($) Mintennce ($) , , , Ice (kg) Pckging ($) Interest on vrile cost Totl vrile cost , , Fixed costs Totl deprecition Interest on fixed cost ($) 10% Tx Totl fixed cost Profit (S) All price/costs re reported in US dollrs for the yer Assume 106-d growing seson for tilpi nd 114-d seson for prwn. systems my show greter dynmics nd greter differences. The circultors used would likely need to e modified to crete more eneficil mixing pttern long more horizontl xis rther thn wshing the pond ottom (Sukenik et l. 1991; Perl nd Tucker 1995; Tucker nd Steey 1995; Boyd 1997). When circultors were removed nd constnt ertion ws supplied, oxygen concentrtions were mintined t optiml levels in CTL nd LDP tretments; however, emergency ertion ws required periodiclly for the HDP tretment. Periods of low nighttime oxygen concentrtions (#2 mg/l) occurred in polyculture ponds during the month of August ut not in the CTL ponds. Future studies should monitor ertion requirements to more precisely determine the effects of incresed stocking densities on oxygen udgets. Tilpi did not crete consistent long-term shift in the percent contriution of lgl groups during the durtion of the experiment. Detiled phytoplnkton counts were mde for smpling dtes previously identified s importnt time periods regrding chnges in phytoplnkton popultion. Phytoplnkton smples were nlyzed to detect chnges in species composition nd iomss to clrify resons for these differences in physicl nd chemicl vriles (Zim et l. 2002). Chlorophytes were the dominnt group in ll tretments throughout the mjority of the experiment. The mjor difference occurred fter circultors were removed on 5 August. The CTL

12 378 DANAHER ET AL. ponds hd n increse in cynoprokryophyt undnce, ut cynoprokryophyt did not ecome dominnt in polyculture tretments (Fig. 4), possily s result of tilpi grzing. Perschcher nd Lorio (1993) found cged tilpi very effective in controlling cynoprokryophyt when stocked t pond surfce re densities of 0.5/m 2, nd Turker et l. (2003) found tilpi feeding hits more effective ginst cynoprokryot thn ginst chlorophytes. As tilpi density incresed, their ility to control the undnce of cillriophytes present in the pond lso incresed; however, fter the removl of circultors, the ility of the tilpi to reduce cillriophytes undnce decresed. It is presumed tht circultors mde these tychoplnktonic ditoms more ccessile to tilpi y keeping them in suspension throughout the wter column, nd fter mechnicl mixing ws stopped, ditoms settled out of the wter column s hs een previously documented (Sukenik et l. 1991). Results show tht feeding hits of Nile tilpi stocked t rtes $5000 fish/h were effective in reducing phytoplnkton cell size on certin smple dtes (Tle 2). Smll cell size cn prevent gill lesions (Lndserg 2002) nd cn lso e eneficil to wter qulity through higher growth rtes nd incresed ssimiltion rtes of nutrients vi incresed cell surfce re (Turker et l. 2003). Polyculture tretments hd higher overll TAN nd nitrite levels thn CTL ponds proly in response to greter totl nutrient inputs for the direct feeding of oth species. However, there were no significnt differences in TAN concentrtions during August when tretments were receiving their highest dily feeding rtes. With three-fold increse in feeding rtes in polyculture, higher unionized mmoni nd ph levels would e expected; however, unionized mmoni levels did not differ mong tretments (Fig. 2). All were within cceptle limits recommended y Strus et l. (1991). This study suggests tht grzed phytoplnkton popultions effectively ssimilted incresed TAN concentrtions, thus keeping wter qulity prmeters within cceptle rnges. Yi nd Fitzsimmons (2004) found tht the presence of tilpi did not ffect phytoplnkton iomss, ut their presence did stilize wter qulity in tilpi shrimp polyculture. Feeding rtes could e responsile for some effect on ph levels mesured during the experiment. Intensifiction cn result in incresed respirtion rtes nd cron dioxide concentrtions from the increse of iologicl ctivity (Boyd nd Tucker 1998). Although cron dioxide levels were not monitored during the experiment, possile increses in cron dioxide concentrtions my hve lso contriuted to lower ph levels in intensified tretments. Future experiments should consider monitoring this dditionl prmeter. Prwn Production In the present study, survivl of freshwter prwn (85%) ws within the rnge, or etter thn, reported in other polyculture studies with tilpi (Cohen nd R nn 1983; Grci-Perez nd Alston 2000; Tidwell et l. 2000; Dos Sntos nd Vlenti 2002) nd other prwn monoculture studies (Dniels nd D Armo 1994; Dniels et l. 1995; Tidwell et l. 2004). Miltner et l. (1983) nd Cohen nd R nn (1983) found tht prwn popultion structure ws independent of free-swimming tilpi. This lso ppers to e true for tilpi grown in cges, s indicted in the present study. Competition for feed hs een prolem in polyculture systems using free-swimming fish (Grci-Perez et l. 2000; Dos Sntos nd Vlenti 2002) nd cn result in chnge in prwn popultion structure (Grci-Perez nd Alston 2000). Grci-Perez nd Alston (2000) found higher frequency of SM in their polyculture tretment (22%) using free-swimming tilpi compred with their prwn monoculture tretment (5%) nd concluded this ws proly ecuse of prwn eing outcompeted for feed. In the present study, the frction of SM ws similr in ll tretments nd mde up only smll percentge (4 6%). In this study, tilpi were grown in cges so competition for feed ws not prolem. Also, oth species were fed seprtely with no reduction in lloctions. Extr food ville to the prwns from uneten fish

13 POLYCULTURE OF CAGED NILE TILAPIA AND PRAWN 379 feed, fish feces, nd incresed nturl productivity must not hve een ove prwn demnds s prwn FCR ctully improved in the polyculture tretments. The dditionl nutrient input in the polyculture ponds ppered to hve the most impct on prwn lte in the production seson. No differences were found in verge weights of prwn during interim smpling. Lrger prwn (.40 g) hve een found to enefit from incresed feed qulity lte in the production seson (Tidwell et l. 2000, 2004). As nturl productivity ecomes depleted, lrger individuls (BC, OC, RF) require lterntive food sources or greter nutrient density, wheres smller individuls (SM) pper less ffected. Both polyculture tretments produced significntly higher percentge of premium prwns ($ 30 g) compred with the CTL. Grci-Perez et l. (2000) found tht 78% of the prwn weighed more thn 20 g, 25% weighed more thn 30 g, nd 19% weighed more thn 40 g in the polyculture tretment with prwns stocked t 7/m 2.Inthepresent study, despite the sme stocking density, polyculture tretments resulted in 93% of the prwns weighing more thn 20 g, 83% weighing more thn 30 g, nd 48% weighing more thn 40 g, indicting tht cged tilpi my e preferred over free-roming tilpi for mrkets requiring lrge-sized prwn. As ws the cse in our study for LDP nd HDP, Wng et l. (1998) found incresed yields of shrimp with incresed tilpi stocking density in net cges. They determined tht tilpi densities of 3200 fish/h nd 400 kg/h positively ffected production of shrimp stocked t 6/m 2. Our findings suggest tht even greter tilpi densities cn hve positive effect on prwn yield, survivl, nd totl pond production. Tilpi Production Both polyculture tretments produced mrketle-size tilpi nd incresed totl pond production (tilpi nd prwn) y 300 nd 492% in the LDP nd HDP, respectively, compred with prwn monoculture. Tilpi survivl verged 96% nd no tilpi recruitment ws oserved in drined ponds. These dt do not clerly indicte reson for the slightly reduced growth rtes of tilpi in the HDP tretment, ut lower nighttime DO levels my hve een the cuse. DO levels elow 2 mg/l sometimes occurred in the HDP tretment during nighttime monitoring (2300 h) fter the removl of circultors. The HDP tretment my hve een pproching crrying cpcity of the pond for this level of ertion (Crro-Anzlott nd McGinty 1986). However, other wter qulity vriles remined cceptle. Clerly, intensifiction rewrds producer with higher profit lthough more cpitl is necessry s production intensifies. This lso trnsltes to producer hving greter flexiility in future price competition in different mrket chnnels. This study indictes tht LDP could gretly increse pond profit (339%) over prwn monoculture. HDP incresed pond profit over the LDP mngement prctice nd prwn monoculture y 165 nd 561%, respectively. However, HDP mngement would proly e much higher risk for the frmer. Grci-Perez et l. (2000) found tht the ddition of tilpi to prwn ponds incresed economic returns y 21% nd the ddition of prwn to tilpi ponds incresed return y 112%. These dt indicte tht polyculture of Nile tilpi in cges with freshwter prwn ctully improves prwn production nd gretly increses totl pond production. Stocking nd feeding rtes, t lest to LDP levels, for the two species pper to e essentilly independent. Future studies should nlyze the polyculture of the freshwter prwn nd free-roming Nile tilpi in temperte ponds. There my e enefits from free-swimming tilpi through etter lge grzing, feeding hits (Cohen et l. 1983; Cost-Pierce et l. 1987), improved wter qulity (Rouse et l. 1987; Azim et l. 2003), nd incresed production (Dos Sntos nd Vlenti 2002; Grci-Perez et l. 2000). Acknowledgments This reserch ws supported y USDA/ CSREES grnt to Kentucky Stte University under greement KYX A. Funding

14 380 DANAHER ET AL. ws lso provided y Kentucky s Regionl University Excellence Trust Fund to the KSU Aquculture Progrm nd y Kentucky Stte University in support of the Mster of Science in Aquculture nd Aqutic Sciences nd served s portion of the senior uthor s mster s thesis. We thnk ll university personnel who ssisted with stocking ponds, dily mngement, nd hrvest of the experiment. Mention of trde nme, proprietry product, or specific equipment does not constitute gurntee or wrrnty y the US Deprtment of Agriculture nd does not imply pprovl of the product to the exclusion of others tht my e ville. Literture Cited Angnostidis, K. nd J. Komrek Modern pproches to the clssifiction system of the cynophytes. 3 Oscilltorilles. Archiv fuer Hydroiologie (50 53): Azim, M. E., M. C. J. Verdegem, M. Singh, A. A. vn Dm, nd M. C. M. Beveridge The effects of periphyton sustrte nd fish stocking density on wter qulity, phytoplnkton, periphyton nd fish growth. Aquculture Reserch 34: Boyd, C. E Wter qulity in ponds for quculture. Alm Agriculturl Experiment Sttion, Auurn University, Alm, USA. Boyd, C. E Prcticl spects of chemistry in pond quculture. The Progressive Fish-Culturist 59: Boyd, C. E. nd C. S. Tucker, editors Pond quculture wter qulity mngement. Kluwer Acdemic Pulishers, Norwell, Msschusetts, USA. Boyd, C. E., J. W. Precher nd L. Justice Hrdness, lklinity, ph nd pond fertiliztion. Proceedings of the 32nd Annul Conference Southestern Assocition of Fish nd Wildlife Agencies 32: Brick, R. W. nd R. R. Stickney Polyculture of Tilpi ure nd Mcrorchium rosenergii in Texs. Proceedings of the World Mriculture Society 10: Crro-Anzlott, A. E. nd A. S. McGinty Effects of stocking density on growth of Tilpi nilotic cultured in cges in ponds. Journl of the World Aquculture Society 17(1 4): Cohen, D. nd Z. R Ann The production of the freshwter prwn, Mcrorchium rosenergii, in Isrel. III. Density effect of ll-mle Tilpi hyrids on prwn yield chrcters in polyculture. Aquculture 35: Cohen, D., Z. R Ann, nd A. Brnes Production of the freshwter prwn, Mcrorchium rosenergii, in Isrel. I. Integrtion into fish polyculture systems. Aquculture 31: Cost-Pierce, B. A., S. R. Mlech, nd E. A. Lws Yield chrcteristics of prwns, Mcrorchium rosenergii (de Mn), with fish polycultures t low feeding rtes. Aquculture nd Fisheries Mngement 18: Coyle, S., J. H. Tidwell, A. VnArnum, nd L. A. Bright A comprison of two feeding technologies in freshwter prwns, Mcrorchium rosenergii, rised t high iomss densities in temperte ponds. Journl of Applied Aquculture 14(1 2): Dniels, W. H. nd L. R. D Armo Pond production chrcteristics of freshwter prwns, Mcrorchium rosenergii, s influenced y the stocking of size-grded popultions of juveniles. Aquculture 122: Dniels, W. H., L. R. D Armo, M. W. Fondren, nd M. D. Durnt Effects of stocking density nd feed on pond production chrcteristics nd revenue of hrvested freshwter prwns, Mcrorchium rosenergii, stocked s size-grded juveniles. Journl of the World Aquculture Society 26(1): Dsgupt, S. nd J. H. Tidwell A rekeven price nlysis of four hypotheticl freshwter prwn, Mcrorchium rosenergii, frms using dt from Kentucky. Journl of Applied Aquculture 14(1/2):1 22. Dtt, S. nd B. B. Jn Control of loom in tropicl lke: grzing efficiency of some herivorous fishes. Journl of Fish Biology 53: Dos Sntos, M. J. M. nd W. C. Vlenti Production of Nile tilpi, Oreochromis niloticus, nd freshwter prwn, Mcrorchium rosenergii, stocked t different densities in polyculture systems in Brzil. Journl of the World Aquculture Society 33(3): Dunseth, D. R Polyculture of chnnel ctfish, Ictlurus puncttus, silver crp, Hypophthlmicthys molitrix, nd three ll-mle tilpis, Srtherodon spp. Doctorl disserttion. Auun University, Auurn, Alm, USA. Grci-Perez, A. nd D. E. Alston Comprisons of mle nd femle morphotypes distriution of freshwter prwn, Mcrorchium rosenergii, in monoculture versus polyculture with Nile tilpi, Oreochromis niloticus. Crien Journl of Science 36(3 4): Grci-Perez, A., D. E. Alston, nd R. Cortes-Mldondo Growth, survivl, yield, nd size distriutions of freshwter prwn, Mcrorchium rosenergii, nd tilpi, Oreochromis niloticus, in polyculture nd monoculture systems in Puerto Rico. Journl of the World Aquculture Society 31(3): Guerrero, R. D. III Control of tilpi reproduction. Pges in R. S. V. Pullin nd R. H. Lowe- McConnell, editors. The iology nd culture of tilpis. ICLARM Conference Proceedings 7. Interntionl Center for Living Aqutic Resource Mngement, Mnil, Philippines.

15 POLYCULTURE OF CAGED NILE TILAPIA AND PRAWN 381 Heinen, J. M., H. Rndll Roinette, nd L. R. D Armo Polyculture of freshwter prwns, Mcrorchium rosenergii, nd chnnel ctfish fingerlings, Ictlurus puncttus, in 1985 in Mississippi. Journl of the World Aquculture Society 18(3): Hepher, B., A. Milstein, H. Leventer, nd B. Teltsch The effect of fish density nd species comintion on growth nd utiliztion of nturl food in ponds. Aquculture nd Fisheries Mngement 20: Hillerrnd, H., C. D. Dürselen, D. Kirschtel, U. Pollingher, nd T. Zohry Biovolume clcultion for pelgic nd enthic microlge. Phycology 35: Lndserg, J. H The effects of hrmful lgl looms on qutic orgnisms. Reviews in Fisheries Science 10(2): Mcgee, M. V. nd C. E. Boyd Evlution of the influence of wter exchnge in chnnel ctfish ponds. Trnsctions of the Americn Fisheries Society 112: Meriwether II, F. H., E. D. Scur, nd E. Y. Okmur Cge culture of red tilpi in prwn nd shrimp ponds. Journl of the World Mriculture Society 15: Miltner, M., A. Grndos, R. Romire, J. W. Avult, Jr, Z. R nn, nd D. Cohen Polyculture of the prwn, Mcrorchium rosenergii, with fingerling nd dult ctfish, Ictlurus puncttus, nd Chinese crps, Hypophthlmichthys molitrix, nd Ctenophrygodon idell, in erthen ponds in south Louisin. Journl of the World Mriculture Society 14: Morirty, C. M. nd J. W. Morirty Quntittive estimtion of the dily ingestion of phytoplnkton y Tilpi nilotic nd Hplochromis nigripinnis in Lke George, Ugnd. Journl of Zoology, London 171: Osunde, I. M., S. D. Coyle, nd J. H. Tidwell Acute toxicity of copper sulfte to juvenile freshwter prwn, Mcrorchium rosenergii. Journl of Applied Aquculture 14(3 4): Perl, H. W. nd C. S. Tucker Ecology of luegreen lge in quculture ponds. Journl of the World Aquculture Society 26: Pgn-Font, F. A Cge culture s mechnicl method for controlling reproduction of Tilpi ure (Steindchner). Aquculture 6: Perschcher, P. W Algl mngement in intensive chnnel ctfish production trils. World Aquculture 26(3): Perschcher, P. W. nd W. J. Lorio Filtrtion rtes of ctfish pond phytoplnkton y Nile tilpi, Oreochromis niloticus. Journl of the World Aquculture Society 24(3): Petersen, J. J Freshwter prwn hrvesting: comprison of three methods. Journl of the World Mriculture Society 13: Pote, J. W., T. P. Cthcrt, nd P. N. Delimn Control of high ph in quculturl ponds. Aquculturl Engineering 9: Prescott, G. W Alge of the western Gret Lkes re. Wm. C. Brown Pulishers, Duuque, Iow, USA. Rouse, D. B. nd R. R. Stickney Evlution of the production potentil of Mcrorchium rosenergii in monoculture nd in polyculture with Tilpi ure. Proceedings of the World Mriculture Society 13: Rouse, D. B., G. O. El Nggr, nd M. A. Mull Effects of stocking size nd density of tilpi on Mcrorchium rosenergii in polyculture. Journl of the World Aquculture Society 18(2): Strus, D. L., H. R. Roinette, nd J. M. Heinen Toxicity of un-ionized mmoni nd high ph to postlrvl nd juvenile freshwter shrimp Mcrorchium rosenergii. Journl of the World Aquculture Society 22(2): Sukenik, A., R. S. Levy, Y. Levy, P. G. Flkowski, nd Z. Duinsky Optimizing lgl iomss production in n outdoor pond: simultion model. Journl of Applied Phycology 3: Tidwell, J. H., S. Coyle, C. Weiel, nd J. Evns Effects nd interctions of stocking density nd dded sustrte on production nd popultion structure of freshwter prwn, Mcrorchium rosenergii. Journl of the World Aquculture Society 30(2): Tidwell, J. H., S. D. Coyle, A. VnArnum, nd C. Weiel Growth, survivl, nd ody composition of cge-cultured Nile tilpi, Oreochromis niloticus, fed pelleted nd unpelleted distillers grins with solules in polyculture with freshwter prwn, Mcrorchium rosenergii. Journl of the World Aquculture Society 31(4): Tidwell, J. H., S. D. Coyle, A. Vn Arnum, nd C. Weiel Production response of freshwter prwns, Mcrorchium rosenergii, to incresing mounts of rtificil sustrte in ponds. Journl of the World Aquculture Society 31(3): Tidwell, J. H., S. D. Coyle, A. VnArnum, nd C. Weiel Effects of sustrte mount nd orienttion on production nd popultion structure of freshwter prwn, Mcrorchium rosenergii in ponds. Journl of the World Aquculture Society 33(1): Tidwell, J. H., S. D. Coyle, nd S. Dsgupt Effects of stocking different frctions of size grded juvenile prwns on production nd popultion structure during temperture-limited growout period. Aquculture 231: Tucker, C. S. nd J. A. Steey Dytime mechnicl wter circultion of chnnel ctfish ponds. Aquculturl Engineering 14: Turker, H., A. G. Eversole, nd D. E. Brune Effect of temperture nd phytoplnkton concentrtion on Nile tilpi Oreochromis niloticus (L.) filtrtion rte. Aquculture Reserch 34: Turker, H., A. G. Eversole, nd D. E. Brune Effect of Nile tilpi, Oreochromis niloticus (L.), size on phytoplnkton filtrtion rte. Aquculture Reserch 34:

16 382 DANAHER ET AL. Utermöhl, H Sur Vervollkommnung der quntittiven phytoplnkton-methodik. Interntionle Vereiningung fur Theoretische und Angewndte Limnologie 9:1 38. Venrick, E. L How mny cells to count? Pges in A. Sourni, editor. Plnkton mnul. SCOR/ UNESCO, Pris, Frnce. Wng, J., D. Li, S. Dong, K.Wng, nd X. Tin Experimentl studies on polyculture in closed shrimp ponds. I. Intensive polyculture of Chinese shrimp, Peneus chinensis, with tilpi hyrids. Aquculture 163: Wester, C. D., K. R. Thompson, A. M. Morgn, E. J. Grisy, nd A. L. Gnnm Use of hempseed mel, poultry y-product mel, nd cnol mel in prcticl diets without fish mel for sunshine ss, Morone chrysops 3 M. sxtilis. Aquculture 188 (3 4): Yi,Y.ndK.Fitzsimmons Tilpi-shrimp polyculture in Thilnd. Pges in R. Bolivr, G. Mir, nd K. Fitzsimmons, editors. New dimensions in frmed Tilpi. Proceedings of ISTA 6. Bureu of Fisheries nd Aqutic Resources, Mnil, Philippines. Zr, J. H Biosttisticl nlysis. Prentice Hll, Englewood Cliffs, New Jersey, USA. Zim, P. V., C. S. Tucker, C. C. Mischke, nd C. C. Grimm Short-term effect of diuron on ctfish pond ecology. North Americn Journl of Aquculture 64:16 23.