UNIVERSITI PUTRA MALAYSIA EFFECT OF WATER QUALITY AND MARINE PHYTOPLANKTON COMMUNITY STRUCTURE ON SHRIMP PRODUCTION IN TROPICAL PONDS

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1 UNIVERSITI PUTRA MALAYSIA EFFECT OF WATER QUALITY AND MARINE PHYTOPLANKTON COMMUNITY STRUCTURE ON SHRIMP PRODUCTION IN TROPICAL PONDS MOHD ROZHAN BIN ZAKARIA FS

2 EFFECT OF WATER QUALITY AND MARINE PHYTOPLANKTON COMMUNITY STRUCTURE ON SHRIMP PRODUCTION IN TROPICAL PONDS By MOHD ROZHAN BIN ZAKARIA Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, in Fulfilment of the Requirements for the Degree of Master of Science June 2009

3 DEDICATION This piece of work is dedicated to my wife and daughter, Rozaini and Raihana, my parents and the rest of my family members for their love, enthusiasm and inspiration ii

4 Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment of the requirement for the degree of Master of Science EFFECT OF WATER QUALITY AND MARINE PHYTOPLANKTON COMMUNITY STRUCTURE ON SHRIMP PRODUCTION IN TROPICAL PONDS By MOHD ROZHAN BIN ZAKARIA June 2009 Chairman: Fatimah Md. Yusoff, PhD Faculty: Science Production of giant black tiger shrimp (Penaeus monodon) in earthen ponds in the tropical region may vary as the pond matures, depending on water quality and phytoplankton community structure. The objectives of the present study were to determine water quality and marine phytoplankton succession in ponds of different ages, to nutritional value of isolated species of a dominant cyanobacterium in the shrimp ponds in comparison with a beneficial diatom and green alga and to investigate how phytoplankton community structure could be affected by alteration of macronutrient concentrations in mixed cultures. The field study was carried out in an intensive shrimp farm in Kuala Selangor, Malaysia. Phytoplankton and water samples were collected from ponds of different ages categorized as new (<1yr), intermediate (2-5yrs) and old (>10yrs), for 16 weeks of shrimp culture. Fluctuation of nutrient and chlorophyll-a concentrations were not different from other tropical iii

5 shrimp ponds in the region. Cyanobacteria (five genera), diatoms (24 genera), dinoflagellates (four genera) and green algae (three genera) were four dominant groups of phytoplankton found in all the shrimp ponds. Diatoms were dominant during the early stage of the culture in new ponds whilst blue green algae dominated intermediate and old ponds throughout the culture period. Shrimp production in new ponds were significantly higher than intermediate and old ponds (p<0.05) probably due to the abundance of diatoms at the beginning of the culture cycle, suitable as live feed for zooplankton and shrimp larvae. Pseudanabaena tenuis was found abundant in all pond categories throughout the culture period. The cyanobacterium was isolated for surface structure and proximate analysis in the laboratory. Result showed that P. tenuis have lower nutritional value in comparison with a common diatom (Chaetoceros calcitrans) and a green alga (Chlorella pyrenoidosa), indicating that is was not part of consumable algae among grazers. All the above microalgae species were used in the nutrient enrichment bioassays in the laboratory to determine the growth and competition among species when grown singly and in mixed cultures. The result showed that the diatom grew well in single cultures and competed successfully over other microalgae in mixed cultures when silica concentrations increased whilst other essential growth nutrients were not limited. This present research gives an idea of how shrimp production in ponds of different ages could be affected by water quality and phytoplankton community structure and how alteration of nutrient concentrations could be use to stimulate growth of beneficial algae and suppress harmful algae in mixed culture systems which need further research for better understandings. iv

6 Abstrak tesis yang dikemukakan kepada senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk ijazah Master Sains KESAN KUALITI AIR DAN STRUKTUR KOMUNITI FITOPLANKTON MARIN KE ATAS PENGELUARAN UDANG DALAM KOLAM TROPIKA Oleh MOHD ROZHAN BIN ZAKARIA Jun 2009 Pengerusi: Fatimah Md. Yusoff, PhD Fakulti: Sains Penghasilan udang harimau (Penaeus monodon) dari kolam-kolam tanah di kawasan tropika mungkin berbeza dengan peningkatan umur kolam, bergantung kepada kualiti air dan struktur komuniti fitoplankton. Objektif kajian ini adalah untuk menentukan kualiti air dan struktur fitoplankton marin pada kolam-kolam udang berlainan umur, mengkaji struktur permukaan serta analisis proksimat spesis sianobakteria dominan dalam kolam udang dengan membuat perbandingan ke atas sejenis diatom dan alga hijau bermanfaat serta mengkaji bagaimana pengubahsuaian kepekatan nutrien boleh memberi kesan ke atas struktur komuniti fitoplankton dalam kultur campuran. Kajian lapangan telah dijalankan di sebuah ladang ternakan udang di Kuala Selangor, Malaysia. Sampel air dan fitoplankton telah diambil dari kolamkolam pelbagai peringkat umur yang dikategorikan sebagai kolam baru (< 1 tahun), v

7 kolam pertengahan (2-5 tahun) dan kolam lama (>10 tahun) selama 16 minggu masa penternakan. Fluktuasi kepekatan nutrien dan klorofil-a tidak berbeza dari ladang ternakan udang lain. Sianobakteria (lima genera), diatom (24 genera), dinoflagelat (empat genera) dan alga hijau (tiga genera), merupakan empat kumpulan besar fitoplankton yang terdapat dalam kolam-kolam tersebut. Diatom merupakan kumpulan dominan dalam kolam baru semasa peringkat awal penternakan udang sementara alga biru hijau adalah dominan di dalam kolam pertengahan dan kolam lama sepanjang tempoh penternakan. Penghasilan udang dalam kolam baru adalah lebih tinggi dengan perbezaan yang nyata (p<0.05) berbanding kolam pertengahan dan kolam lama, yang berkemungkinan disebabkan oleh kelimpahan diatom yang sesuai sebagai makanan hidup untuk zooplankton dan larva udang semasa peringkat awal penternakan. Pseudanabaena tenuis didapati mempunyai kelimpahan yang tinggi dalam setiap kategori kolam sepanjang tempoh penternakan. Sianobakterium tersebut telah dipencilkan untuk kajian struktur permukaan dan analisis proksimat di dalam makmal. Keputusan mendapati bahawa P. tenuis mempunyai nilai nutrisi yang rendah jika dibandingkan dengan sejenis diatom (Chaetoceros calcitrans) dan alga hijau (Chlorella pyrenoidosa) di mana ianya menunjukan bahawa sianobakterium tersebut bukanlah pilihan sebagai makanan hidup di kalangan peragut. Kesemua spesies mikroalga tersebut telah digunakan untuk bioesei nutrien di dalam makmal untuk mengetahui pertumbuhan dan persaingan setiap spesies apabila dikultur secara berasingan dan di dalam kultur campuran. Keputusan menunjukan bahawa diatom tersebut mempunyai pertumbuhan yang baik serta mampu mengatasi spesis mikroalga lain dengan peningkatan kepekatan silika sementara kepekatan nutrien lain yang penting untuk pertunbuhan adalah tanpa had. Penyelidikan terkini ini telah menyumbang kepada idea bagaimana kualiti air dan struktur komuniti fitoplankton vi

8 boleh memberi kesan ke atas penghasilan udang dalam kolam yang berlainan peringkat umur. Penyelidikan ini juga membolehkan kita mengetahui bagaimana pengubahsuaian kepekatan nutrien boleh meningkatkan pertumbuhan alga yang berguna di samping mengurangkan pertumbuhan alga yang tidak dikehendaki di dalam sistem kultur campuran yang memerlukan kajian lebih lanjut untuk pemahaman yang lebih berkesan. vii

9 AKCNOWLEDGEMENTS My deepest appreciation and thanks go to the Chairperson of my supervisory committee, Professor Fatimah Md. Yusoff who provided me most of my needs throughout the whole study. I am very grateful and pleased to be working under her guidance. I have learned a lot from her constructive criticisms, and encouragement, and I am grateful for the financial support, and individual understanding. Not only I have reached towards the end of this piece of work, but her support and guidance is well maintained along the path in the beginning of my career as an academic staff of UPM. I am grateful to be provided with excellent expertise and valuable suggestions from my supervisory committee members, Professor Dr. Suhaila Mohamed and Professor Dr. Fauziah Othman. I hope that this cooperation will always continue in accomplishing future research and projects. My special thanks are dedicated to Dr. Sanjoy Banerjee, Dr. Hamid Rezai, Mr. Perumal Kuppan, Mrs. Noraini Mohd Ain, Ms. Azilah Jalil and Mrs. Noormawaty for their technical support and guidance during sample processing, image analyzing and taxonomic study. Not to forget a very unique appreciation goes to Professor Shariff Mohamed Din in providing me equipment and facilities throughout my whole study. Not to forget my dearest friends (Jamal, Natrah, Hazel, Dr. Helena, Prabath, Dr. Omid, Liza, Jimmy, Zafri, Kamil, Murni, Zarirah, Dr. Ina Salwany, Dr. Syed, Siti Anarita, Azreen, Siti Zubaidah and many more) and family who never stops encouraging me for the best in my life. viii

10 I certify that an Examination committee met on 16 th June 2009 to conduct the final examination of Mohd Rozhan Bin Zakaria on his degree thesis entitled Marine Phytoplankton Community Structure of Tropical Shrimp Ponds in accordance with Universiti Pertanian Malaysia (Higher Degree) Act 1980 and Universiti Pertanian Malaysia (Higher Degree) Regulations The committee recommends that the candidate be awarded the Master of Science. Members of Examination Committee are also as follows: Aziz Arshad, PhD Associate Professor Faculty of Agriculture Universiti Putra Malaysia (Chairman) Siti Khalijah Daud, PhD Associate Professor Faculty of Science Universiti Putra Malaysia (Internal Examiner) Mustafa Kamal Abd. Satar, PhD Faculty of Agriculture Universiti Putra Malaysia (Internal Examiner) Ann Anton, PhD Professor Biotechnology Research Institute Universiti Malaysia Sabah Malaysia (External Examiner) BUJANG KIM HUAT (Ph. D) Professor/ Deputy Dean School of Graduate Studies Universiti Putra Malaysia Date: ix

11 This thesis submitted to the Senate of Universiti Putra Malaysia has been accepted as fulfilment of the requirements for the degree of Masters of Science. The members of the Supervisory Committee were as follows: Fatimah Md. Yusoff, PhD Professor Faculty of Science Universiti Putra Malaysia (Chairperson) Suhaila Mohamed, PhD Professor Faculty of Food Science and Technology Universiti Putra Malaysia (Member) Fauziah Othman, PhD Professor Faculty of Medicine and Health Sciences Universiti Putra Malaysia (Member) HASANAH MOHD. GHAZALI, (PhD) Professor and Dean School of Graduate Studies Universiti Putra Malaysia Date: 16 October 2009 x

12 DECLARATION I declare that the thesis is my original work except for quotations and citations which have been duly acknowledged. I also declare that it has not been previously, and is not concurrently, submitted for any other degree at Universiti Putra Malaysia or at any other institution. MOHD ROZHAN BIN ZAKARIA Date: xi

13 TABLE OF CONTENTS Page DEDICATION ABSTRACT ABSTRAK ACKNOWLEDGEMENTS APPROVAL SHEETS DECLARATION FORMS LIST OF TABLES LIST OF FIGURES LIST OF ABBREVIATIONS ii iii v viii ix xi xiv xvi xxi CHAPTER 1 INTRODUCTION 1 2 LITERATURE REVIEW 2.1 Phytoplankton in the Shrimp Pond Environment 2.2 Characteristics of Aquaculture Ponds of Different Age 2.3 Role of Physico-Chemical Factors on Phytoplankton Succession in Shrimp Ponds Temperature Salinity ph Dissolved Oxygen Specific Conductivity Water Transparency Total Ammonia-Nitrogen (TAN) Nitrate+Nitrite-Nitrogen Phosphorus Dissolved Silica 2.4 Image Analysis of Microalgae 2.5 Nutritional Value of Microalgae 2.6 Phytoplankton Competition and Succession in Mixed Culture 2.7 Effects of Silica Enrichment on Diatom Growth and Succession xii

14 WATER QUALITY AND PHYTOPLANKTON COMMUNITY SUCCESSION IN TROPICAL SHRIMP PONDS OF DIFFERENT AGES 3.1 Introduction 3.2 Materials and Methods Study Area Field Study Physico-Chemical Analysis Phytoplankton Sampling, Sedimentation and Enumeration Data Analysis 3.3 Results 3.4 Discussion 3.5 Conclusion SURFACE STRUCTURE AND NUTRITIONAL PROPERTIES OF SELECTED CULTURED MICROALGAE SPECIES 4.1 Introduction 4.2 Materials and Methods Sample Collection Isolation, Purification and Culture of Microalgae Image Analysis of the Microalgae Surface Structure Proximate Analysis Data Analysis 4.3 Results 4.4 Discussion 4.5 Conclusion MICROALGAE COMMUNITY SUCCESSION IN A NUTRIENT ENRICHMENT BIOASSAY 5.1 Introduction 5.2 Materials and Methods Experiment Experiment Experiment Data Analysis 5.3 Results 5.4 Discussion 5.5 Conclusion GENERAL DISCUSSION, CONCLUSION AND RECOMMENDATION FOR FUTURE RESEARCH REFERENCES 152 APPENDICES 177 BIODATA OF STUDENT 183 LIST OF PUBLICATIONS 184 xiii

15 LIST OF TABLES Table Generalized scenario of management regimes in selected test shrimp ponds in Kuala Selangor shrimp farm Mean of shrimp production (kg/ha) with standard error for each pond category after harvesting in one production cycle (four months study period). Physical parameters (temperature, salinity, ph, dissolved oxygen, specific conductivity and water transparency) readings in new, intermediate and old ponds during the culture cycle. Concentrations of total ammonia nitrogen=tan, nitrate+nitrite nitrogen=no 3 +NO 2 -N, total phosphorus=tp, orthophosphate phosphorus= PO 4 -P, dissolved silica=si and chlorophyll-a=chl-a in new, intermediate and old ponds during the culture cycle. Values are means±standard errors. Mean total density of the four major groups of phytoplankton in new, intermediate and old ponds during the culture cycle (cells ml -1 ). Checklist of phytoplankton genera according to groups found in new, intermediate and old ponds in Kuala Selangor Shrimp Farm during one shrimp production cycle. Values represent mean total density (cells ml -1 )± std error of the mean (n=3). Number of genera, dominant genus and density (mean±standard error of the mean) of four identified phytoplankton groups (Bacillariophyceae, Cyanophyceae, Pyrrophyceae and Chlorophyceae) in new, intermediate and old aged ponds during one shrimp production cycle (16 weeks). General optimum range of physical parameters of environmental conditions for culturing microalgae Means±std errors of biochemical composition for Pseudanabaena tenuis, Chaetoceros calcitrans and Chlorella pyrenoidosa cultured in Conway medium. Page xiv

16 Maximum specific growth rate (µ day -1 ±std error) of Pseudanabaena tenuis, Chaetoceros calcitrans and Chlorella pyrenoidosa achieved during the 14 days of culture. All species were cultured using natural seawater treated with 0 (-ve control), 15, 20, 25 mg L -1 Si and Conway medium (+ve control). Means of maximum specific growth rate (µ day -1 ±std error) of Pseudanabaena tenuis, Chaetoceros calcitrans and Chlorella pyrenoidosa achieved during the 14 days of culture when grown singly. All species were cultured using Conway medium treated with 25 mg L -1 Si. Means of maximum specific growth rate (µ day -1 ±std error) of Pseudanabaena tenuis, Chaetoceros calcitrans and Chlorella pyrenoidosa achieved during the 14 days of culture when grown in mixed cultures with respective combinations. All species were cultured using Conway medium treated with 25 mg L -1 Si. Maximum specific growth rate (µ day -1 ±std error) of Pseudanabaena tenuis, Chaetoceros calcitrans and Chlorella pyrenoidosa achieved during the 14 days of culture. All species were cultured using Conway medium treated with 0 (-ve vontrol), 4, 15, 30 and 45 mg L -1 Si xv

17 LIST OF FIGURES Figure Location of Kuala Selangor, Selangor where the study was carried out. Randomize counting of: left, every stripe and right for every second stripe. Temperature readings in new, intermediate and old ponds during one shrimp production cycle within the study period. Bars indicate standard error (±) of the mean, n=9 ponds. Salinity readings in new, intermediate and old ponds during one shrimp production cycle within the study period. Bars indicate standard error (±) of the mean, n=9 ponds. ph readings in new, intermediate and old ponds during one shrimp production cycle within the study period. Bars indicate standard error (±) of the mean, n=9 ponds. Dissolved oxygen readings in new, intermediate and old ponds during one shrimp production cycle within the study period. Bars indicate standard error (±) of the mean, n=9 ponds. Specific conductivity readings in new, intermediate and old ponds during one shrimp production cycle within the study period. Bars indicate standard error (±) of the mean, n=9 ponds. Water transparency readings in new, intermediate and old ponds during one shrimp production cycle within the study period. Bars indicate standard error (±) of the mean, n=9 ponds. Total ammonia nitrogen concentrations in new, intermediate and old ponds during one shrimp production cycle within the study period. Bars indicate standard error (±) of the mean, n=9. Page xvi

18 Nitrate+nitrite nitrogen concentrations in new, intermediate and old ponds during one shrimp production cycle within the study period. Bars indicate standard error (±) of the mean, n=9 ponds. Total phosphorus concentrations in new, intermediate and old ponds during one shrimp production cycle within the study period. Bars indicate standard error (±) of the mean, n=9 ponds. Orthophosphate-phosphorus concentrations in new, intermediate and old ponds during one shrimp production cycle within the study period. Bars indicate standard error (±) of the mean, n=9 ponds. Dissolved silica concentrations in new, intermediate and old ponds during one shrimp production cycle within the study period. Bars indicate standard error (±) of the mean, n=9 ponds. Chlorophyll-a concentrations in new, intermediate and old ponds during one shrimp production cycle within the study period. Bars indicate standard error (±) of the mean, n=9 ponds. Mean total density of phytoplankton in new, intermediate and old ponds in one shrimp production cycle (16 weeks). Bars indicate standard error (±) of the mean. Superscript letters indicates significant level at p<0.05. Growth of four major groups of phytoplankton in new ponds during 16 weeks of the shrimp culture. Bars indicate standard error (±) of the phytoplankton mean total density. Growth of four major groups of phytoplankton in intermediate ponds during 16 weeks of the shrimp culture. Bars indicate standard error (±) of the phytoplankton mean total density. Growth of four major groups of phytoplankton in old ponds during 16 weeks of the shrimp culture. Bars indicate standard error (±) of the phytoplankton mean total density xvii

19 Filaments of Pseudanabaena tenuis viewed as (A) image under a light microscope (magnification= X 1000) and (B) scanning electron micrograph (15KV, magnification= X 10000); CW=cross-wall, TC=terminal cell. Note the single trichome of P. tenuis which forms from single cells arranged uniserially and attached together at the crosswall. Cell(s) of Chaetoceros calcitrans viewed as (A) image under a light microscope (magnification= X 1000) and (B) scanning electron micrograph (15KV, magnification= X 2200); S=setae, C=cigulum. Note the setae of C. calcitrans which arises from the corners at the valve edges and could be seen clearly using a scanning electron microscope but hardly observed under the light microscope. Cell (s) of Chlorella pyrenoidosa viewed as (A) image under a light microscope (magnification= X 1000) and (B) scanning electron micrograph (15KV, magnification= X 3000). Note small green spherical (S) in a single cell of the alga viewed under the light microscope (arrow) and the patchy surface observed in the scanning electron micrograph (arrow). Growth of Pseudanabaena tenuis, Chlorella pyrenoidosa and Chaetoceros calcitrans in control treatment (0 mgl -1 Si) after 14 days of culture. All three species were grown in a mixed culture using natural filtered seawater. Bars indicate standard error (±) of the mean. Growth of Pseudanabaena tenuis, Chlorella pyrenoidosa and Chaetoceros calcitrans) in 15 mgl -1 Si treatment after 14 days of culture. All three species were grown in a mixed culture using natural filtered seawater. Bars indicate standard error (±) of the mean. Growth of Pseudanabaena tenuis, Chlorella pyrenoidosa and Chaetoceros calcitrans in 20 mgl -1 Si treatment after 14 days of culture. All three species were grown in a mixed culture using natural filtered seawater. Bars indicate standard error (±) of the mean. Growth of Pseudanabaena tenuis, Chlorella pyrenoidosa and Chaetoceros calcitrans in 25 mgl -1 Si treatment after 14 days of culture. All three species were grown in a mixed culture using natural filtered seawater. Bars indicate standard error (±) of the mean xviii

20 Growth of Pseudanabaena tenuis, Chaetoceros calcitrans and Chlorella pyrenoidosa and in Conway medium (+ve control) after 14 days of culture. All three species were grown in a mixed culture using natural filtered seawater. Bars indicate standard error (±) of the mean. Growth of Pseudanabaena tenuis, Chlorella pyrenoidosa and Chaetoceros calcitrans during 14 days of culture using Conway medium. All species were grown singly (separated cultures). Bars indicate standard error (±) of the mean. Growth of Pseudanabaena tenuis and Chaetoceros calcitrans during 14 days of culture using Conway medium. Both species were grown in a mixed culture. Bars indicate standard error (±) of the mean. Growth of Pseudanabaena tenuis and Chlorella pyrenoidosa during 14 days of culture using Conway medium. Both species were grown in a mixed culture. Bars indicate standard error (±) of the mean. Growth of Chaetoceros calcitrans and Chlorella pyrenoidosa during 14 days of culture using Conway medium. Both species were grown in a mixed culture. Bars indicate standard error (±) of the mean. Growth of Pseudanabaena tenuis, Chlorella pyrenoidosa and Chaetoceros calcitrans during 14 days of culture using Conway medium. All three species were grown in a mixed culture. Bars indicate standard error (±) of the mean. Growth of Pseudanabaena tenuis, Chlorella pyrenoidosa and Chaetoceros calcitrans without silica (negative control) after 14 days of culture. All three species were grown in a mixed culture using natural filtered seawater added with Conway medium nutrient composition. Bars indicate standard error (±) of the mean. Growth of Pseudanabaena tenuis, Chlorella pyrenoidosa and Chaetoceros calcitrans in 4 mgl -1 Si after 14 days of culture. All three species were grown in a mixed culture using natural filtered seawater added with Conway medium nutrient composition. Bars indicate standard error (±) of the mean xix

21 Growth of Pseudanabaena tenuis, Chlorella pyrenoidosa and Chaetoceros calcitrans in 15 mgl -1 Si after 14 days of culture. All three species were grown in a mixed culture using natural filtered seawater added with Conway medium nutrient composition. Bars indicate standard error (±) of the mean. Growth of Pseudanabaena tenuis, Chlorella pyrenoidosa and Chaetoceros calcitrans in 30 mgl -1 Si after 14 days of culture. All three species were grown in a mixed culture using natural filtered seawater added with Conway medium nutrient composition. Bars indicate standard error (±) of the mean. Growth of Pseudanabaena tenuis, Chlorella pyrenoidosa and Chaetoceros calcitrans in 45 mgl -1 Si after 14 days of culture. All three species were grown in a mixed culture using natural filtered seawater added with Conway medium nutrient composition. Bars indicate standard error (±) of the mean xx

22 LIST OF ABBREVIATIONS ANOVA Chl-a 1DHA DO EPA N NaNO 2 NH 3 + NH 3 -N + NH 4 - NO 2 PL PUFA rpm SFA SGR TAN TP analysis of variance Chlorophyll-a docosahexaenoic acid dissolved oxygen eicosapentaenoic acid north anhydrous sodium nitrite ammonia ammonia-nitrogen ammonium nitrite postlarvae polyunsaturated fatty acid rotation per minute saturated fatty acid specific growth rate total ammonia nitrogen total phosphorus xxi

23 CHAPTER 1 INTRODUCTION 1.1 BACKGROUND OF THE STUDY Intensive marine shrimp farming has steadily increased over the last decades in order to meet the world s market demand although the industry has suffered major problems in sustaining the growth of shrimp aquaculture such as disease outbreak, environmental degradation and poor management. Marine shrimp, the giant black tiger prawn, Penaeus monodon has attracted much attention from aquaculturists in the Asia and Pacific region due to the technological breakthroughs in its life cycle control (Samocha, 2004), the development of a variety of commercial feeds along with the establishment of more efficient farming practices and firm market prices and demand (Kuperan, 1988). However, according to Sampaio et al (as cited in Case, Lec, Leitao, Anna, Schwamborn, and Junior, 2008), rapid development in the shrimp aquaculture industry has been accompanied by increasingly controversial debates over the environmental, social, and economic impacts. In Malaysia, P. monodon production varies from one farm to the other depending on the pond sediment quality, water source and application of responsible aquaculture practices (FAO, 1997). Yusoff et al. (2002) demonstrated that shrimp production was closely related to the quality of the water used for the shrimp farming. Water quality in shrimp ponds usually deteriorates with the progressed culture period due to the accumulation of 1

24 organic matter from excess feed and metabolites. Briggs and Funge-Smith (1994) reported that only 15% of the feed was converted into fish flesh whilst the rest went into the water and sediment. Changes in water quality and increased availability of nutrients affect the phytoplankton composition in shrimp ponds. Phytoplanktons are microscopic algae which have the ability to float and derive light as the source of energy to produce their own food. These organisms are the primary producers in the aquatic environment. It is accepted by pond managers that shrimp production is better if there is a stable and relatively high abundance of beneficial phytoplankton species such as diatoms and low in harmful ones such as cyanobacteria and dinoflagellates (Alonso-Rodriguez and Paez-Osuna, 2003). Noxious species of blue-green algae like Oscillatoria spp., Pseudanabaena spp. and Microcystis spp. caused water deterioration and give bad odor to shrimp flesh (Izaguirre and Taylor, 1998), whilst certain species of dinoflagellates such as Alexandrium tamarense, has been reported to cause mortality of Penaeus monodon in Taiwan in 1989 (Huei-Meei et al., 1993). On the other hand, diatom species such as Chaetoceros calcitrans, and Skeletonema costatum and certain chlorophytes such as Chlorella sp., Tetraselmis tetrahele, Isochrysis sp. and Nannochloropsis oculata have long been used as live feeds in aquaculture as they are highly nutritious especially in long-chain polyunsaturated fatty acids (PUFA s) (Brown et al., 1989; Molina Grima et al., 1995; Viron et al., 2000). In semi intensive shrimp farming system with large ponds, these live feeds are most likely important as a food source than the meager amount starter feed that the farmers habitually throw into the pond at the beginning of the rearing cycle (Fujimura, 1991). Therefore, in most aquaculture system such as marine shrimp ponds, fertilizers are often applied to promote 2

25 beneficial phytoplankton growth (Alonso-Rodriguez and Paez-Osuna, 2003). This is accomplished by repeated small amounts of fertilizers that results in an N:P ratio of 20:1 (Boyd and Daniels, 1994). If the nutrients are not consistently supplied, depression of phytoplankton population will occur and consequently cause slow growth of the marine shrimp itself (Hunter et al., 1987). Yusoff et al. (2002) reported that there was a shift from the dominance of beneficial phytoplankton species at the beginning of culture period, to the noxious species of cyanobacteria after a month of culture. Species succession in aquatic environments starts with small flagellates and diatoms, followed by dinoflagellates which are relatively bigger in size. Cyanobacteria are usually the dominant species at the final step as they can thrive under stressful conditions for other organisms and when nitrogen compounds are scarce. Phytoplankton succession either in the field or experiments such as in mixed cultures is important as some researchers argue that studying the behavior of phytoplankton in pure cultures are particularly unnatural since the phytoplankton community is never wholly monospecific (Fogg and Brenda, 1987). Experiments were done to determine the interaction, competition and succession between different species of phytoplankton in a mixed culture towards environmental factors such as temperature, light intensity and nutrient availability. Harrison and Davis (1979) analyzed factors influencing species selection outdoor for continuous phytoplankton cultures while studies by D Elia et al. (1979) and Regan and Ivancic (1984) dealt with mixed cultures under laboratory conditions. However, there is a paucity of information on growth characteristics, biochemical composition and nutritive value of mixed culture 3