Extensive Net Cage Culture of Nile Tilapia (Oreochromis niloticus) Fingerlings in Nutrient-enriched Pond

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1 W. Jiwym Our Nture / Our Nture (2012) (2012) 10: : Extensive Net Cge Culture of Nile Tilpi (Oreochromis niloticus) Fingerlings in Nutrient-enriched Pond W. Jiwym Progrm of Fisheries, The School of Science nd Technology, Nong Khi Cmpus, Khon Ken University, Nong Khi Province, Thilnd E-mil:wirjiw@kku.c.th Abstrct To investigte the potentil of extensive net cge culture for Nile tilpi (Oreochromis niloticus) fingerlings, n experiment ws conducted in net cges suspended in fertilized pond. Mixed-sex popultion of Nile tilpi with n verge initil body weight of g ws used to stock in experimentl cges. Four tretments; non dded-substrte without supplementl feeding (NSNF), non dded-substrte with supplementl feeding (NSAF), dded-substrte without supplementl feeding (ASNF), nd dded-substrte with supplementl feeding (ASAF) were tested. The results indicted tht ddition of substrtes which gve n dditionl submerged surfce re of pproximtely equl to the totl cge surfce re did not show significnt effect on the growth (p > 0.05). The fish gross yield obtined from non dded-substrte cges without supplementl feeding ws 1.22 kg/m 3 for 56-dy period. Key words: Wstewter tretment, periphyton-bsed quculture, fish nursing, communl wter resource, sustinle quculture Introduction Studies hve shown tht dding rtificil substrtes for periphyton growth in pondbsed culture systems cn increse the production of some cultured species (Hem nd Avit, 1994; Wh et l., 1999; Rmesh et l., 1999; Azim et l., 2001; Azim et l., 2001b; Keshvnth et l., 2001; Keshvnth et l., 2004). Consequently, the provision of substrtes could reduce the need for supplementl feeding nd tht substrtes hd positive effect on fish survivl (Keshvnth et l., 2002). More specificlly, periphyton my be n lterntive or complement for supplementry feed in fingerling production (Keshvnth et l., 2004). However, most previous studies were conducted in quculture pond systems, while those few 61 studies tht were conducted in cge conditions still hve some recommendtions for further studies (Huchette et l., 2000; Huchette nd Beveridge, 2003). Even though experiments hve demonstrted tht fish production from ponds hving periphyton substrtes is higher thn tht from substrte-free controls (Hem nd Avit, 1994; Wh et l., 1999; Keshvnth et l., 2001b; Azim et l., 2002; Azim et l., 2002b), production results with tilpi in periphyton systems hve been mixed (Keshvnth et l., 2004). High production ws reported in cdj systems in West Afric with blckchin tilpi (Srotherodon melnotheron; Hem nd Avit, 1994), but no significnt effect of periphyton ws found in n experimentl

2 system with Nile tilpi (Oreochromis niloticus; Shresth nd Knud-Hnsen, 1994; Norberg, 1999). Uddin (2007) noted tht the ddition of periphyton substrtes resulted in higher Nile tilpi production. However, these re ll the results from pond-bsed systems. In ddition to grzing on phytoplnkton they feed on benthic nd ttched lgl nd detritus (Bowen, 1981; 1982), therefore wide rnge of feeding hits nd sources of food vilility in pond systems my led to mixed production results of tilpis. Moreover, the previous studies of periphyton-bsed cge culture concerned grow-out production, which seems to require higher periphyton production in ech culture unit in comprison with erly or even dvnced nursing in cges. Consequently, it remins to be demonstrted whether periphyton grzing is significnt nd cost effective mens of incresing the food supply for the production of tilpi fry nd fingerling stges in cges (Huchette et l., 2000). In Thilnd, the demnd for Nile tilpi fingerlings is incresing long with the use of cge culture; however, the supply of dequtely sized fingerlings tends to be mjor constrint. Mny cge frms now prefer to be stocked by lrger sized fingerlings s their shortened grow-out period mens lower feed costs nd less susceptibility to dverse culture environment risks. To supply this demnd, mny frm ponds re being used to rise Nile tilpi fingerlings t the nursing stge; however, problems hve been encountered over the qulity nd size vritions of the fingerlings s well the high levels of mortlity due to hrvesting techniques. To ddress the issues of qulity nd size nd thus improve the efficiency of these nursing systems, the use of net cges with dded W. Jiwym / Our Nture (2012) 10: substrtes in nutrient enriched wter is of interest. If the ddition of rtificil substrtes in cges cn increse growth when compred to free-substrte controls, it would be n lterntive choice for fingerling production. Furthermore, if dily feeding is considered lorious mngement prctice in fish fry nursing, then substrte-bsed cge system would be more prcticl. However, the use of net cge culture in nutrient enriched ponds or other wter bodies would be both eco-friendly nd low-cost quculture technique. Therefore, the purpose of this study ws to determine the growth performnces of Nile tilpi fingerlings cultured in net cges suspended in nutrient-enriched pond under different mngement prctices. Mterils nd methods The experiment ws crried out during Februry to April 2010 t the Nong Khi Cmpus of Khon Ken University in Thilnd s Nong Khi province. Squre net cges mde of blue nylon netting with 1- mm mesh size nd mesuring 1 x 1 x 1.2 m, were used s experimentl units. The submerged volume of ech cge ws 1 m 3. All were suspended from bmboo structure in 400-m 2 fertilized fish pond. Added-substrtes cges were provided with bmboo poles (men dimeter 5 cm, length 50 cm) which were hung nd suspended verticlly into the cges, t totl density of 13 poles per cge, nd which give n dditionl submerged surfce re pproximtely equl to the totl cge surfce re. Prior to the experiment, the pond ws renovted, nd ll lrger qutic nimls were erdicted by frequent netting. It ws then treted with lime (CCO 3 ) t the rte of 250 kg/h. After 1 week of liming, it ws

3 then fertilized with cow mnure, ure nd triple super phosphte (TSP) t the rte of 2000, 100 nd 100 kg/h (80, 4, nd 4 kg per 400 m 2 -pond), respectively. It continued therefter to be fertilized t fortnightly intervls t hlf of the initil rte (40, 2 nd 2 kg per pond). The cow mnure ws pplied t the four corners of the pond, while the ure nd TSP were soked together with wter for 6 hours nd then spred over the wter surfce. On the sme dy of the first fertiliztion, bmboo poles were suspended into the dded-substrte cges. The cges were left for 10 dys to llow plnkton development in the wter column nd periphyton growth on bmboo poles, nd the stocked with the fish. Four tretments; non dded-substrte without supplementl feeding (NSNF), non dded-substrte with supplementl feeding (NSAF), dded-substrte without supplementl feeding (ASNF), nd ddedsubstrte with supplementl feeding (ASAF) were tested. A mixed-sex popultion of Nile tilpi, O. niloticus fries (individul weight g) were stocked t 500 fish per cge (1 m 3 ). Ech tretment ws tested in triplicte. Experimentl fish were stocked fter 10 dys of substrte instlltion, nd fish from ll tretments were hrvested fter 56 dys. Supplementry feed ws 2:1 rtio mixture of locl rice brn nd fish mel. Crude protein content of the mixture ws nlyzed (AOAC, 2005) nd the verge vlue ws 27.7%. Supplementry feed ws mnully delivered 2 times, 09:00 nd h dily t 10% body weight of the fish throughout the experimentl period. The feed ws djusted biweekly bsed on the bulk weight of the fish estimted from smple of 25 individuls. All the fish were weighed t the beginning nd end of the experiment. The W. Jiwym / Our Nture (2012) 10: finl verge weight (g) of the individul fish in ech cge ws estimted by dividing the totl finl biomss in the cge by the number of survivors. Totl weight increments (net yield) were estimted by deducting the biomss stocked from the biomss hrvested nd ws expressed s kg/m 3. The specific growth rte (%/d) ws clculted s: (lnw 2 lnw 1 )/t x 100, where W 1 is the initil live body weight (g), W 2 is the finl live body weight (g) nd t is the time in dys. Survivl rte (%) ws clculted s: (no. of fish hrvested/no. of fish stocked) x 100. The wter qulity in the experimentl cges nd pond ws monitored fortnightly between 09:00 nd 10:00 h on ech smpling dy with the wter temperture nd dissolved oxygen (YSI model 52), nd ph nd conductivity (Hch model sension 5) being recorded. Wter smples from the experimentl cges nd pond were collected fortnightly nd nlyzed for chlorophyll (cetone extrction), totl mmoni nitrogen (phente method), nitrite-n (dizotiztion), nitrte (cdmium reduction nd dizotiztion), soluble rective phosphorus (scorbic cid method) nd totl phosphorous (persulfte digestion nd scorbic cid finish) ccording to Stndrd Methods for the Exmintion of Wter nd Wstewter (APHA, 1989). Totl lklinity nd totl hrdness from the experimentl cges were mesured t monthly intervls (APHA, 1989). After 10 dys of substrte instlltion, periphyton smples were collected nd therefter continued to be tken t fortnightly intervls. For ech smpling time, one pole from ech cge ws selected rndomly. From ech pole, one smple ( 10 x10 cm-bnd of periphyton) ws tken t the middle depth (50 cm beneth wter

4 W. Jiwym / Our Nture (2012) 10: surfce) for dry mtter nd sh-free dry mtter contents nlyses. After collection of the periphyton smples, the poles were returned to their originl position nd mrked so tht smpled poles were lwys excluded from subsequent smples. Dry mtter (DM) ws determined by drying the smples overnight t 105 C to constnt weight, upon which sh content ws determined using muffle furnce (4 h t 540 C). The finl weight of the crucible long with the remins ws weighed for clcultion of the sh nd sh-free dry mtter (AFDM). The dt on finl men weight, specific growth rte nd survivl rte were compred using nlysis of vrinces (ANOVA) nd Tukey-HSD test. The ssumptions of norml distribution nd homogeneity of the vrinces were checked before nlyses. The differences were considered sttisticlly significnt t n lph level of Vritions of tretment mens re presented in men ± stndrd devition. Results Tle 1 shows growth nd survivl of Nile tilpi from ll tretments for 56-d nursing period of the experiment. Survivl ws not significntly different mong tretments (p > 0.05), nd ws higher thn 83%. Adding substrtes did not ffect on growth (p > 0.05), while supplementry feed showed significnt effect on growth (p < 0.05). The higher specific growth rte of the fish obtined from cges provided with supplementry feed but no significnt difference ws observed between dded nd non-dded substrte cges. Fish yields were significntly higher in cges provided with feed either with substrte or without substrte (p < 0.05). There ws no significnt difference in periphyton biomss (DM or AFDM) between ASNF nd ASAF tretments for ech smpling dy (p > 0.05). Periphyton biomss tended to decrese rpidly fter fish stocking nd then fter the 2nd week of experiment ws reltively stle nd less likely to fluctute (Fig. 1 nd 2). Periphyton biomss in dry mtter or sh free dry mtter of ASNF nd ASAF tretments decresed significntly fter fish stocking (p < 0.05). The verge dry mtter periphyton of the two tretments before, nd two weeks fter, fish stocking were pproximtely nd mg/cm 2, respectively. Averge periphyton dry mtter or s free dry mtter between ASNF nd ASAF tretments throughout the culture period ws not significntly different (p > 0.05). The verge vlues re summrized nd given in Tle 2. The wter qulity prmeters mesured during the experiment were summrized nd given in tle 3. For ech wter qulity prmeter, there ws no significnt difference between tretments nd open pond wter during experiment. Averge chlorophyll concentrtions mesured in cges of ll tretments tended to increse fter the 2nd week of the experiment (Fig. 3). The verge chlorophyll concentrtion mesured in cges ws ± µg/l Discussion All the wter qulity prmeters in experiment were within the cceptle rnges, s recommended for tropicl quculture (Boyd, 1982; Boyd nd Tucker, 1992; Beveridge, 1996). There ws no interction effect between the ddition of substrtes nd supplementry feed on the growth prmeters of the fingerlings. The 64

5 W. Jiwym / Our Nture (2012) 10: ddition of substrtes lone did not show significnt effect on the growth, while supplementry feeding could improve growth of the fish in dded or non-dded substrte cges. The results indicte tht periphyton production cn not replce or Tle 1. Growth prmeters of Nile tilpi fry over 56-dy period in cges. All vlues re mens ± SD. Growth prmeters Tretments NSNF NSAF ASNF ASAF Hrvest (no. fish) 414± ± ± ±7.07 Finl men weight (g) 3.00± ±1.15 b 2.81± ±0.26 b Specific growth rte (%/d) 6.82± ±0.38 b 6.71± ±0.08 b Survivl (%) ± ± ± ±1.41 Gross yield (kg/m 2 ) 1.22± ±0.55 b 1.34 ± ±0.08 b Net yield (kg/m 2 ) 1.19± ±0.55 b 1.31± ±0.08 b Men vlues with different letters in the sme row re significntly different (p<0.05) by Tukey-HSD. Tle 2. Averge periphyton biomss in dry mtter (DM) nd sh free dry mtter (AFDM) throughout 56-dy period (n = 15). All vlues re mens ± S.D. (rnge). DM (mg/cm 2 ) AFDM (mg/cm 2 ) ASNF 0.333±0.163 ( ) 0.111±0.057 ( ) ASAF 0.373±0.217 ( ) 0.126±0.117 ( ) Men vlues with different letters in the sme column re significntly different (Tukey HSD) ASNF ASAF Dry mtter (mg cm -2 ) b Feb. 8 Mr. 15 Mr. 29 Mr. 8 Apr. Smpling dtes Figure 1. Averge periphyton dry mtter during the experimentl period. Vlues re the mens ±SD) of three replicted cges per smpling dte (n = 3) in ech tretment. 65

6 W. Jiwym / Our Nture (2012) 10: ASNF ASAF Ash-free dry mtter (mg cm -2 ) b Feb. 8 Mr. 15 Mr. 29 Mr. 8 Apr. Smpling dtes Figure 2. Averge periphyton sh free dry mtter during the experimentl period. Vlues re the mens ±SD of three replicted cges per smpling dte (n = 3) in ech tretment Chlorophyll (µg l -1 ) Feb. 8 Mr. 15 Mr. 29 Mr. 8 Apr. Smpling dtes Figure 3. Averge chlorophyll concentrtion of wter column in different tretments during the experimentl period. Vlues re the mens ±SD of three replicted cges per smpling dte (n = 3) in ech tretment

7 W. Jiwym / Our Nture (2012) 10: Tle 3. Averge wter qulity prmeters mesured in cges nd in open pond wter during experiment. All vlues re mens ± SD Prmeters Inside cges In open pond (n = 12) (n = 48) Dissolved oxygen (mg/l) 4.30± ±1.15 ph 8.87± ±0.46 Conductivity (µs/cm) 252.4± ±49.6 Temperture ( 0 C) 26.81± ±1.68 Totl mmoni (mg/l) 0.16± ±0.03 Nitrite-nitrogen (mg/l) 0.25± ±0.31 Nitrte-nitrogen (mg/l) 1.50± ±1.70 Totl nitrogen (mg/l) 3.29± ±1.57 Soluble rective phosphorus (mg/l) 0.91± ±0.54 Totl phosphorous (mg/l) 1.62± ±0.53 Totl lklinity (mg/l) ± ±21.14 Totl hrdness (mg/l) ± ±2.44 complement supplementl feeding in net (6.82 %/dy) ws obtined from NSNF cge culture system. This finding is tretment in the present study. different from study on the effects of However the use of periphyton in bmboo substrtes nd supplementl quculture is bsed on the finding tht feeding on the growth nd production of mny herbivorous fish prefer feeding on hybrid red tilpi fingerlings which ws benthic, epilithic or periphytic lge, rther conducted in ponds. In tht experiment it thn on smll phytoplnkton (Horn, 1989; ws found tht periphyton could replce or vn Dm et l., 2002). Beveridge nd Bird complement supplementl feeding in tilpi (2000) hve shown tht Nile tilpi is fingerling culture (Keshvnth et l., periphyton grzer lthough tilpis hve 2004). been primrily described s filter feeders on In the present study, the survivl rtes of phytoplnkton (Morirty nd Morirty, the fish from ll tretments rnged from ; Bocci, 1999). Stomch content 96% which ws higher thn tht of nlysis of tilpis grown in cges in the previous study by Little et l. (2003) on Meghn River showed tht they were both dvnced nursing of mixed-sex nd monosex filter feeders nd grzers (Hutchette et l., tilpi fry in hps. In tht experiment, 2000). The proportion of ech feeding mode the survivl rtes mong ll of the tretment ws difficult to determine, but visul groups rnged from 69 86%. Additionlly, estimte of gut contents suggested higher tht study found tht the specific growth contribution from periphyton (Huchette nd rte of Nile tilpi fry (initil men weight Beveridge, 2003). However, filter feeding 0.13g) rised in hps suspended in mechnism cn occur nturlly during fish fertilized pond t stocking density of 150 respirtion whilst the intke of fish/m 2 with supplementry feeds ( mixture supplementry feed or periphyton is rther of lyer-duck concentrte mnufctured by selective feeding. Therefore, when filter Chroen Pokphnd Co. nd fine rice brn, 2: feeding cn serve their nutritionl 1 rtio by volume) t 5% dily rtion for requirements, then the fish will not feed 2-month period ws 6.2%/dy (Little et l., selectively on other food sources. 2003). While, higher specific growth rte 67 63

8 The results from n erlier periphytonbsed cge experiment showed tht the verge AFDM of periphyton in the uppermost 50 cm of the wter column ws 0.36 mg/cm 2 (Huchette nd Beveridge, 2003). This vlue is high when compred to the verge periphyton AFDM throughout the culture period in the present study of 0.12 mg/cm 2. However, when the periphyton biomss in the present study of 0.24 mg/cm 2 before fish stocking is considered, significnt decrese in periphyton biomss fter fish stocking indicted tht the fish consumed periphyton, while no significnt difference in periphyton biomss between ASNF nd ASAF tretments for ech smpling dy my indicte the sme grzing rte for both groups of the fish. But no significnt difference in growth performnces ws observed mong the tretments, were provided with substrte or not indicting tht ddition of substrte t pproximtely equl to cge surfce re ws not sufficient for significntly incresing in periphyton production. Becuse the sh (10 19%), protein (23 26%) nd energy (19 20 KJ/g) contents of the estimted periphyton cn be considered s brodly pproprite to fish dietry needs (Azim et l., 2002b). While crude protein content of the supplementry feed in the present study ws pproximtely 27.7%. Yields obtined in extensive cge quculture in the Philippines rnge from 0.05 to 1.25 kg/m 3 /month without input (Beveridge, 1996), nd re in greement with study on technicl nd economicl evlution of periphyton-bsed cge culture of tilpi (Oreochromis niloticus) in tropicl freshwter cges which gve yields of 0.12 to 0.24 kg/m 3 /month (Huchette nd Beveridge, 2003). The fish gross yields W. Jiwym / Our Nture (2012) 10: obtined from NSNF tretment in the present study ws 1.22 kg/m 3 for the 56-dy period, which is equivlent to 0.61 kg/m 3 /month. The vlues were higher thn those of the previous studies. Even the difference ws clerly due to different growth phse of the experimentl fish. However, the results show the potentil use of extensive cge net cge culture in nutrient-enriched wter bodies; e.g. quculture ponds, communl wter bodies nd nutrient-enriched lkes; prticulrly for Nile tilpi fingerling production. Bse on the results, it my be concluded tht dding substrtes, which give n dditionl submerged surfce re pproximtely equl to the totl cge surfce re is not sufficient for periphyton production, nd for good growth of Nile tilpi fingerling net cge culture system. And even supplementry feeding gve higher yield when compred to no feeding cges, but either provision of substrtes or supplementry feed could led to higher production cost. In the present study, finl weight of the fish from ll tretments rnged from g, nd this finl weight is not likely to ffect mrket price of the fingerlings. In the present study, initil stocking density of the fish ws 500 fish/m 3 ; however, reducing fish density my increse growth of the fish. Becuse the vilility of nturl food could decrese t the high fish densities nd possibly result in nutrition deficiencies (Coulibly et l., 2007). In conclusion, n extensive net cge culture in nutrient-enriched pond shows high potentil in erly nursing of Nile tilpi. Acknowledgements The Aqutic Animls Reserch Center, Nong Khi cmpus, Khon Ken University re cknowledged for the provision of

9 mterils, equipments nd reserch fcilities. The uthor lso thnks Mr. Puny Dchrt nd Miss. Nisrt Tippydr, School of Sciences nd Technology, Nong Khi Cmpus, Khon Ken University, for their excellent technicl ssistnces during the course of the experiment. References AOAC Officil methods of nlysis of AOAC interntionl. 18 th edn. Githersburg, Mrylnd, USA, AOAC Interntionl. APHA Stndrd methods for the exmintion of wter nd wstewter. 17 th edn. Americn Public Helth Assocition, Wshington, DC. Azim, M. E., M. A. Wh, A. A. vn Dm, M. C. M. Beveridge nd M. C. J. Verdegem The potentil of periphyton-bsed culture of two Indin mjor crps, rohu Leo rohit nd goni Leo gonius (Linneus). Aquc. Res. 32: Azim, M. E., M. A. Wh, A. A. vn Dm, M. C. M. Beveridge, E. A. Huismn nd M. C. J. Verdegem. 2001b. Optimiztion of stocking rtios of two Indin mjor crps, rohu (Leo rohit Hm.) nd ctl (Ctl ctl Hm.) in periphyton-bsed quculture system. Aquculture 203: Azim, M. E., M. C. J. Verdgem, M. M. Rhmn, M. A. Wh, A. A. vn Dm nd M. C. M. Beveridge Evlution of polyculture of Indin mjor crps in periphyton-bsed ponds. Aquculture 213: Azim, M. E., M. A. Wh, M. C. J. Verdegem, A. A. vn Dm, J. M. vn Rooij nd M. C. M. Beveridge. 2002b. The effects of rtificil substrtes on freshwter pond productivity nd wter qulity nd the implictions for periphytonbsed quculture. Aqut. Liv. Resour. 15: Beveridge, M. C. M Cge quculture. 2 nd edn. Fishing News, Oxford. Beveridge, M. C. M. nd D. J. Bird Diet, feeding nd digestive physiology. In: Tilpi: Biology nd exploittion (Eds. M.C.M Beveridge nd B.J. McAndrew), Kluwer Acdemic Publishing, Dordrecht, Netherlnds. pp Bocci, M Modelling the growth of Nile tilpi (Oreochromis niloticus) feeding on nturl resources in enclosures in Lgun de By (Philippines). Ecol. Model. 119: W. Jiwym / Our Nture (2012) 10: Bowen, S. H Digestion nd ssimiltion of periphytic detritl ggregte by Tilpi mossmbic. Trns. Amer. Fish. Soc. 110: Bowen, S. H Feeding, digestion nd growthqulittive considertions. In: The Biology nd Culture of Tilpis, vol. 7. (Eds. R. S. V. Pullin nd R. H. Lowe-McConnell), ICLARM Conf. Proc., Int. Center for Living Aqutic Resources Mngement, Mnil, Philippines. pp Boyd, C. E Wter qulity mngement for pondfish culture. Elsevier, Amsterdm. Boyd, C. E. nd C. S. Tucker Wter qulity nd pond soil nlyses for quculture. Auburn University, AL. Coulibly, A., I. N. Outtr, T. Koné, V. N Doub, J. Snoeks, B. G. Gooré nd E. P. Kouméln First results of floting cge culture of the Africn ctfish Heterobrnchus longifilis Vlenciennes, 1840: Effect of stocking density on survivl nd growth rtes. Aquculture 263: El-Syed, A.F.M, S. I. Teshim Protein nd energy requirements of Nile tilpi, Oreochromis niloticus, fry. Aquculture 103 (1): Hem, S. nd J. L. B. Avit First results on cdjs enclos s n extensive quculture system (West Afric). Bull. Mr. Sci. 55: Hepher, B Nutrition of pond fishes. Cmbridge University Press. Horn, M. H Biology of mrine herbivorous fishes. Ocenogr. Mr. Biol. Ann. Rev. 27: Huchette, S. M. H., M. C. M. Beveridge, D.J. Bird nd M. Irelnd The impcts of grzing by tilpis (Oreochromis niloticus L.) on periphyton communities growing on rtificil substrte in cges. Aquculture 186: Huchette, S. M. H. nd M. C. M. Beveridge Technicl nd economicl evlution of periphyton-bsed cge culture of tilpi (Oreochromis niloticus) in tropicl freshwter cges. Aquculture 218: Keshvnth, P., B. Gnghdr, T. J. Rmesh, J. M. Vn Rooij, M. C. M. Beveridge, D. J. Bird, M. C. J. Verdegem nd A. A. vn Dm The potentil of rtificil reefs to enhnce production of herbivorous fish in Indin freshwter pondspreliminry trils. Aquc. Res. 32: Keshvnth, P., B. Gnghdr, T. J. Rmesh, J. M. Vn Rooij, M. C. M. Beveridge, D. J. Bird, M. C. J. Verdegem nd A. A. vn Dm. 2001b. Use of

10 W. Jiwym / Our Nture (2012) 10: rtificil substrtes to enhnce production of freshwter herbivorous fish in pond culture. Aquc. Res. 32 (3): Keshvnth, P., B. Gngdhr, T. J. Rmesh, A. A. vn Dm, M. C. M. Beveridge nd M. C. J. Verdegem The effect of periphyton nd supplementl feeding on the production of the indigenous crps Tor khudree nd Leo fimbritus. Aquculture 213: Keshvnth, P., B. Gngdhr, T. J. Rmesh, A. A. vn Dm, M. C. M. Beveridge nd M. C. J. Verdegem Effects of bmboo substrte nd supplementl feeding on growth nd production of hybrid red tilpi fingerlings (Oreochromis mossmbicus x Oreochromis niloticus). Aquculture 235: Little, D.C., R. C. Bhujel nd T. A. Phm Advnced nursing of mixed-sex nd mono-sex tilpi (Oreochromis niloticus) fry, nd it impct on subsequent growth in fertilized ponds. Aquculture 221: Morirty, C. M. nd D. J. Morirty Quntittive estimtion of the dily ingested of phytoplnkton by Tilpi nilotic nd Hplochromis nigripinnis in Lke George, Ugnd. J. Zool. (London) 171: Norberg, J Periphyton fouling s mrginl energy source in tropicl tilpi cge frming. Aquc. Res. 30: Rmesh, M. R., K. M. Shnkr, C. V. Mohn nd T. J. Vrghese Comprison of three plnt substrtes for enhncing crp growth through bcteril biofilm. Aquc. Eng. 19: Shresth, M. K. nd C. F. Knud-Hnsen. (1994) Incresing ttched microorgnisms biomss s mngement strtegy for Nile tipi (Oreochromis niloticus) production. Aquc. Eng. 13: Uddin, M. S Mixed Culture of Tilpi (Oreochromis niloticus) nd Freshwter Prwn (Mcrobrchium rosenbergii) in Periphyton-bsed Ponds. PhD Thesis, Wgeningen University, The Netherlnds. vn Dm A. A., M. C. M. Beveridge, M. E. Azim nd M. C. J. Verdegem The potentil of fish production bsed on periphyton. Rev. Fish Biol. Fish. 12: Wh, M. A., M. E. Azim, M. H. Ali, M. C. M. Beveridge nd S. Khn The potentil of periphyton-bsed culture of the ntive mjor crp clbush, Leo clbs (Hmilton). Aquc. Res. 30: