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ACF - INTERNATIONAL NET WORK




The subsistence fishfarming
in Africa: Technical Manual




       Yves FERMON



       ...
Cover photos:
Ö Top right: Tilapia zillii - © Anton Lamboj
Ö Top left: Pond built by ACF in DRC, 2008 - © François Charrie...
OBJECTIVES OF THE MANUAL
 Ö The objective of the handbook is to bring to the essential elements for the installa-
 tion of...
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  1. 1. ACF - INTERNATIONAL NET WORK The subsistence fishfarming in Africa: Technical Manual Yves FERMON In collaboration with: Aımara
  2. 2. Cover photos: Ö Top right: Tilapia zillii - © Anton Lamboj Ö Top left: Pond built by ACF in DRC, 2008 - © François Charrier Ö Bottom: Beneficiaries in front of the pond they have done, Liberia, ASUR, 2006 - © Yves Fermon ii Subsistence fishfarming in Africa
  3. 3. OBJECTIVES OF THE MANUAL Ö The objective of the handbook is to bring to the essential elements for the installa- tion of production of animal proteins “fish” to lower costs in relation to the existing natural resources and with a minimum of external contributions. This in a context of subsistence. Ö In this case, it is a question above all of proposing an information system strategic plan of a system making it possible to produce consumable fish in the shortest pos- sible time, and with lower costs to mitigate the lack of animal proteins. This does not prevent the installation of structures having a certain durability. The unit must be adapted to the environmental context. In this work, it is a question of providing a guide: ¾ To program managers and their technical teams, ¾ To managers at headquarters to monitor the success of programs. This manual covers: Ö The various stages of setting up a «fishfarming» program, As of the arrival on the ground, it is a question of evaluating the renewable resources present, the needs for the populations and the already existing supply in fish. Then, a whole process is connected involving the technical sides of the installation of fish ponds, follow-ups of the biological aspects of the ponds. Finally, it is a question of managing and of carrying out a follow-up of the ponds and production of fish. Ö The constraints that must be taken into account by the field actors. Various constraints will influence the choice for the development of fish production or not and what kind of techniques for a good fit with human needs and the environment. They are environmen- tal, in conjunction with the available resources, geomorphology, climate and hydrology of the area of intervention. But they are also a social and cultural development, with the beliefs and taboos, land issues and laws. The fact that, according the region of intervention, the ethnic and social groups and countries, modes of intervention will be different. WHY ANOTHER HANDBOOK? Several organizations have published manuals for the establishment of fish farms in Africa. The first books calling systems in place at the time of the colonial system, but as a fish produc- tion for food self-sufficiency. However, after many trials, the majority of them has proved unsustai- nable in the longer term, for various reasons. The studies undertaken by different agencies of national or international research as the World- Fish Center (formerly ICLARM), CIRAD, IRD (ex ORSTOM), Universities of Louvain and Liège ... have provided evidence concerning the failures and have provided solutions and contributions to knowle- dge in both technical, social or biological species used. However, looking at all the works, one can put forward four points: 9 Most handbooks are intended for production systems of fish for sale, involving: ¾ A temporal investment which can become important and which leads to a professio- nalisation. This requires a technology with the appropriate training of technicians on aspects of reproduction, nutrition or health of fish, either for the establishment of systems to produce food to feed all the fish... Application requires external inputs whose supply may become a barrier for small producers. ¾ Financial investment for, sometimes, land, establishment of ponds, the use of workers, qualified technicians… Subsistence fishfarming in Africa III
  4. 4. 9 The handbooks do not take account of the local biodiversity. Indeed, many introductions and movements of species were made with the intention to set up farms and caused significant disrup- tion to the balance of ecological systems. 9 Whereas these documents present solutions which appear universal, the great variation of the geomorphology, hydrology and the climate in Africa will make that there exist conditions very different according to the zones from interventions. 9 Few works also reflect the socio-ethnological aspects. Educational levels, beliefs and cultures of different peoples and the appropriation of this type of project by the people is often put forward, despite real progress in recent years. 9 Most of these books are made for aspects related to development and therefore with a po- tentiality of longer temporal installation. LIMITS OF THIS HANDBOOK This handbook is primarily a guide to give to the actors the stages and procedures to be followed. However, it will be necessary to adapt these stages and procedures according to the context in which the actions will be undertaken: 9 From a social, cultural and political point of view ¾ Culture and belief Food taboos exist, to varying degrees in all cultures. It is obvious that food, the basic element for the subsistence of man, is a field where the distinction between allowed and forbidden, the pure and impure, is fundamental for health reasons, moral or symbolic systems. ¾ Local law Each country is governed by laws concerning wildlife protection and movement of species from one region to another. These laws can be enacted at the regional level and at all administrative levels, to the village itself. They may be linked to land issues. 9 From an environmental point of view: ¾ Biodiversity and available resources The fauna of African fish includes over 3200 described species belonging to 94 families, but all are not exploitable. The distribution is not uniform across the continent and some species are known only of well delimited zones. For example, the African Great Lakes have a fauna whose majority of the species are endemic there. This means to act with a good knowledge of the fauna compared to the potentially exploitable species and the ecological risks of damages that could be related to the establishment of a fishfarming. ¾ Geomorphology, climate and hydrology If wildlife is so diverse across the continent, it is the result of historical and geological events that led Africa over millions of years. This has caused major hydrological changes. On a smaller time scale, climate variations are crucial for the viability of a fish. The availability of water, with its different uses (drinking, domestic, agriculture ...) is a limiting factor and a source of conflict. The type of terrain and the nature of the soils of the region will lead to technical problems for the achievement of the pond it will be solved. THE STEPS The first handbook is intended for internal use to Action Against Hunger network, therefore, with restricted diffusion. If possible and requests, a handbook with corrections and revisions will be proposed later. Then, an external diffusion to ACF could be considered. iv Subsistence fishfarming in Africa
  5. 5. ACRONYMS ACF/AAH: Action Contre la Faim / Action Against Hunger AIMARA: Association de spécialistes oeuvrant pour le développement et l’application des connaissances sur les poissons et les rela- tions Homme-Nature APDRA-F: Association Pisciculture et Développement Rural ASUR: Association d’Agronomie et Sciences Utiles à la Réhabilitation des populations vulnérables CIRAD: Centre de coopération Internationale en recherche Agrono- mique pour le Développement CNRS: Centre national de la recherche scientifique FAO: Food and Agriculture Organization of the United Nations IRD: Institut de Recherche pour le Développement MNHN: Muséum national d’Histoire naturelle UNO: United Nation Organisation NGO: Non Governemental Organisation GIS: Geographic Informatic System BDC: Biological Diversity Convention IBI: Integrity Biological Indice DRC: Democratic Republic of Congo (ex-Zaïre) Subsistence fishfarming in Africa V
  6. 6. Aımara Association of specialists working for the development and the application of knowledge on fish and Man-Nature relationships The aquatic environments and the management of water represent one of the major stakes for the decades to come. The fish are a source of proteins of good quality for the human consumption, but also a source of income considerable for the developing as developed countries. However, demography, the urban development, the installation of the rivers, industrialization, the climate changes, deforestation… have irreversible consequences on the water courses and the biodi- versity and thus on the men who live of these resources. Ö Goals Research 9 To acquire new ichthyologic knowledge - systematic, biology, ecology, ethology… - on the fresh water, brackish and marine species; 9 To highlight knowledge and practices relating to fishing and management of the biodi- versity and their modes of transmission. Diffusion of knowledge 9 To disseminate the results to the local populations, the general public and the scientific community by publications, exhibitions, contacts with the media and Internet. Sustainable management of environment and resources 9 To sensitive by using the social, cultural, food, economic and patrimonial values of the species with the aim of the conservation, of the management and of the preservationof the biodiversity; 9 To collaborate with the local actors in the durable management of the aquatic resources. Ö Scope of activities • Studies of the characteristics of environments and impacts; • Studies of the biology, biogeography, ecology and behavior of species; • Anthropological and socio-economic relations man - Nature studies; • Ecosystem modeling, statistical analysis: • Development of databases; • Expertise and faunistic inventories. Association AÏMARA 50 avenue de La Dhuys 93170 Bagnolet - FRANCE association.aimara@gmail.com vi Subsistence fishfarming in Africa
  7. 7. ACKNOWLEDGEMENTS Ö ACF Devrig VELLY - Senior Food Security advisor, AAH Cédric BERNARD - Food Security advisor in DRC, AAH François CHARRIER - Food Security advisor in DRC, AAH, Rereader Ö Aimara François MEUNIER - Emeritas Professor at MNHN, President of AIMA- RA, Rereader Patrice PRUVOST - Secretary of AIMARA Hélène PAGÉZY - Researcher, CNRS Ö Other collaborators Roland BILLARD - Emeritas Professor at MNHN, Rereader Didier PAUGY - Research Director at IRD Thierry OBERDORFF - Research Director at IRD Jérome LAZARD - Research Director at IRD Alain BARBET - Agronomist Anton LAMBOJ - Researcher, University of Vienna, Austria. Mickael NEGRINI - Fishfarming technician Kirk WINNEMILLER - Researcher, University of Texas, USA Étienne BEZAULT - Researcher, EAWAG, Switzerland Fabien NANEIX - Teacher Subsistence fishfarming in Africa VII
  8. 8. CONTENTS Part I - INTRODUCTION AND THEORICAL ASPECTS 1 Chapter 01 - FISHFARMING: AIM AND ISSUES 3 I. WHY? 3 II. PRESSURE ON THE RESOURCES 6 II.1. Modifications of the habitat 6 II.2. Water pollution 8 II.3. Fisheries impact 9 II.4. Introductions 9 III. INTERNATIONAL ASPECTS 12 IV. OBJECTIVE OF FISHFARMING 13 Chapter 02 - TYPE OF FISHFARMING 15 I. VARIOUS TYPES OF FISHFARMING 15 II. SOME HISTORY… 17 III. A FISHFARMING OF SUBSISTENCE: GOAL AND PRINCIPLE 17 IV. POLYCULTURE VS MONOCULTURE 18 Chapter 03 - BIOGEOGRAPHY AND FISH SPECIES 21 I. GEOGRAPHY 21 II. THE SPECIES 21 II.1. The Cichlidae 22 II.2. The Siluriformes or catfishes 23 II.3. The Cyprinidae 23 II.4. Other families and species 24 SUMMARY - PART 01 25 Part II - PRACTICAL ASPECTS 27 Chapter 04 - THE INITIAL PRE-PROJECT ASSESSMENT 33 I. THE ECOSYSTEM 33 II. THE ASSESSMENT 36 III. PRINCIPLE 37 IV. BIOLOGICAL AND ECOLOGICAL ASSESSMENT 38 V. SOCIO-ETHNOLOGY 40 V.1. Socio-economic and cultural characteristics 40 viii Subsistence fishfarming in Africa
  9. 9. V.2. The relations man-resources 40 V.3. The relations man-man 41 Chapter 05 - VILLAGES AND SITES SELECTIONS 43 I. THE VILLAGES SELECTION 43 II. THE SITES SELECTION 45 II.1. The water 45 II.2. The soil 50 II.3. The topography 53 II.4. The other parameters 56 Chapter 06 - CHARACTERISTICS OF THE PONDS 59 I. DESCRIPTION 59 II. TYPES OF PONDS 59 II.1. Barrage ponds 62 II.2. Diversion ponds 62 II.3. Comparison 62 III. CHARACTERISTICS 63 III.1. General criteria 63 III.2. Pond shape 66 III.3. According the slope 67 III.4. Layout of ponds 67 III.5. Size and depth of the ponds 68 III.6. Differences in levels 69 IV. SUMMARY 71 Chapter 07 - THE CONSTRUCTION OF POND 73 I. THE DESIGN PLAN 73 II. THE CLEANING OF THE SITE 75 III. WATER SUPPLY: WATER INTAKE AND CHANNEL 77 IV. DRAINAGE: CHANNEL OF DRAINING AND DRAINAGE 81 V. THE PICKETING OF THE POND 82 VI. THE CONSTRUCTION OF THE DIKES 83 VII. THE DEVELOPMENT OF THE PLATE (BOTTOM) 89 VIII. THE CONSTRUCTION OF THE POND INLET AND OUTLET 90 VIII.1. Pond inlet structures 90 VIII.2. Pond outlet structures 94 VIII.3. Sedimentation tank 105 Ix. ADDITIONAL INSTALLATIONS 106 Ix.1. The anti-erosive protection 106 Ix.2. The anti-erosive fight 107 Ix.3. Biological plastic 108 Subsistence fishfarming in Africa Ix
  10. 10. Ix.4. The fence 108 Ix.5. The filling of the pond and tests 109 x. NECESSARY RESOURCES 109 x.1. Materials 109 x.2. Human Resources and necessary time 110 xI. SUMMARY 112 Chapter 08 - BIOLOGICAL APPROACH 113 I. THE LIFE IN A POND 113 I.1. Primary producers 115 I.2. The invertebrates 116 I.3. The vertebrates 118 II. THE FERTILIZATION 118 II.1. The fertilizers or manure 118 II.2. The compost 121 III. SUMMARY 126 Chapter 09 - THE HANDLING OF THE FISH 127 I. CATCH METHODS 127 I.1. Seine nets 129 I.2. Gill nets 132 I.3. Cast nets 133 I.4. Dip or hand nets 134 I.5. Traps 135 I.6. Handline and hooks 136 II. THE TRANSPORT OF LIVE FISH 136 III. THE PRODUCTION OF FINGERLINGS OF TILAPIA 139 III.1. The recognition of the sex 139 III.2. The nursery ponds 139 III.3. Hapas and cages 142 III.4. The other structures 145 IV. THE STOCKING OF THE PONDS 146 V. THE FOLLOW-UP OF FISH 149 VI. DRAINING AND HARVEST 150 VI.1.Intermediate fishings 150 VI.2. Complete draining 151 VII. SUMMARY 152 Chapter 10 - MAINTENANCE AND MANAGEMENT OF THE PONDS 153 I. THE MAINTENANCE OF THE PONDS 153 I.1. The diseases of fish 153 I.2. The feeding of the fish 158 I.3. Daily activities of follow-up 162 I.4. Maintenance work after draining 163 x Subsistence fishfarming in Africa
  11. 11. I.5. Fight against predators 164 I.6. Summary 164 II. THE TECHNIQUES OF CONSERVATION AND OF TRANSFORMATION 165 III. THE MANAGEMENT OF PONDS 167 III.1. Fish Stocks and useful indices for monitoring 167 III.2. The expected yields 168 III.3. The management of harvests 168 III.4. Several kinds of production costs 170 III.5. Record keeping and accounting 170 III.6. The formation 171 IV. PONDS AND HEALTH 171 GENERAL SUMMARY 173 REFERENCES 177 GLOSSARY 179 APPENDIx 187 Appendix 01 - ExAMPLES OF FILES 189 I. FILES FOR MONITORING THE PONDS 189 II. FILES FOR THE FOLLOW-UP OF THE FISH 191 Appendix 02 - TABLE OF DATA 193 Appendix 03 - SOME ELEMENTS OF THE BIOLOGY OF THE SPECIES 207 I. THE MORPHOLOGY AND THE SYSTEMATIC 207 II. THE BIOLOGY OF CICHLIDAE 216 II.1. The taxonomy 216 II.2. The feeding habits 217 II.3. The reproduction and parental care 218 III. THE BIOLOGY OF SILURIFORMES OR CATFISH 226 III.1. The Clariidae 226 III.2. The Claroteidae and Auchenoglanididae 231 III.3. The Schilbeidae 233 III.4. The Mochokidae 233 IV. THE OTHER FAMILIES 234 IV.1. The Cyprinidae 234 IV.2. The Citharinidae 234 IV.3. The Distichodontidae 236 IV.4. The Channidae 236 IV.5. The Latidae 237 IV.6. The Arapaimidae 237 Appendix 04 - BIOGEOGRAPHIC DATA 239 Appendix 05 - FILE OF SPECIES 255 Subsistence fishfarming in Africa xI
  12. 12. LIST OF FIGURES Part I - INTRODUCTION AND THEORICAL ASPECTS 1 Figure 1. World capture and aquaculture production (FAO, 2007). 3 Figure 2. Inland capture fisheries by continent in 2004 (FAO, 2007). 5 Figure 3. Aquaculture production by regional grouping in 2004 (FAO, 2007). 5 Figure 4. Relative contribution of aquaculture and capture fisheries to food fish consumption (FAO, 2007). 6 Figure 5. GIS assessment of potential areas for production fish farms in Africa. 14 Figure 6. Continuum Aquaculture - Fishery en relation with the investment intensification. 19 Figure 7. The ichthyoregions and the countries. 22 Part II - PRACTICAL ASPECTS 27 Figure 8. General implementation plan. 32 Figure 9. Setting of fish ponds: 1. Assessment. 34 Figure 10. Water cycle. 35 Figure 11. Contextual components of the assessment. 36 Figure 12. Setting of fish pond: 2. Selections. 44 Figure 13. Volume of a pond. 46 Figure 14. Water loss through evaporation by weather. 46 Figure 15. Water loss by ground. 46 Figure 16. Flow measurement for small rivers. 47 Figure 17. Measurement of section of the river. 47 Figure 18. Measurement of speed V of the river. 47 Figure 19. Examples of factors that may affect water quality. 48 Figure 20. Secchi disk. 49 Figure 21. Impermeability of clay and sandy soils. 50 Figure 22. Test of the ball (1). 51 Figure 23. Test of the ball (2). 51 Figure 24. Test of soil permeability. 52 Figure 25. Identification of potential water supplies, drainage options, individual valleys, comparison of the various good sites for the installation of ponds, vision of the bottoms (CIRAD). 53 Figure 26. Water supply by gravity. 54 Figure 27. Type of slopes and constraints. 55 Figure 28. Hill slope. 55 Figure 29. Measurement of a slope: Device. 57 Figure 30. Measurement of a slope: Calculation. 57 Figure 31. Example of location of a pond in relation of the house. 58 Figure 32. Setting of fish pond: 3. Ponds. 60 Figure 33. Main components of a pond. 61 Figure 34. Cross section of a ponds. 61 Figure 35. Examples of barrage ponds. 64 Figure 36. Examples of diversion ponds. 65 Figure 37. Disposition of ponds in relation to the topography (CIRAD). 66 Figure 38. Optimization of the surface / work (CIRAD). 66 Figure 39. Example of pond whose shape is adapted to the topography. 67 Figure 40. Disposition and shape of ponds according the slope. 67 Figure 41. Layout of ponds. In series; In parallel. 67 Figure 42. Maximal and minimal depth of a pond. 69 Figure 43. The different points for the management of water by gravity. 70 Figure 44. Level differences. 70 Figure 45. Classical plan a diversion ponds. 71 Figure 46. Examples of diversion fishfarm. 72 xii Subsistence fishfarming in Africa
  13. 13. Figure 47. Setting of fish pond: 3. Ponds. 74 Figure 48. Visualization by picketing of the first plan of possible water supply, possible drainage, of diffe- rents valley (CIRAD). 75 Figure 49. Preparation of the site of the pond. 76 Figure 50. Cleaning of the site. 76 Figure 51. Water levels differences. 78 Figure 52. Setting of the water supply channel. 79 Figure 53. Transverse profile of the channel. Measure and slope of sides. 79 Figure 54. Channel digging. 80 Figure 55. Setting of draining channel. 81 Figure 56. Level of draining channel. 81 Figure 57. Picketing of the pond and the dikes. 82 Figure 58. Cleaning of the zones where the dikes will be build. 83 Figure 59. Definition of the different types of dikes. 83 Figure 60. Description and proportion of a dike (of 1 m high). 83 Figure 61. Pressure difference on a dike. 84 Figure 62. Dikes. Good high; Dikes too small. 84 Figure 63. Digging of the cut-off trench for clay core. 85 Figure 64. Clay core and saturation of the dikes. 85 Figure 65. High of a dike. Depth; Freeboard; Settlement. 85 Figure 66. High of the structure. 85 Figure 67. Dimension of a dike. 86 Figure 68. Calculation of the slope of the dikes. 87 Figure 69. Construction of the dikes (I). Traditionnal - By blocks. 88 Figure 70. Construction the dikes (II). 88 Figure 71. Preparation of the bottom. 88 Figure 72. The bottom or plate. Direction of the slope and drain setting: In ray; As «fish bones». 89 Figure 73. Bottom drain. 90 Figure 74. Cross cut of a pond at the bottom drain. 90 Figure 75. Cross cut of the inlet of a pond. 91 Figure 76. Pipe inlet. 91 Figure 77. End of bamboo pipe. 91 Figure 78. Gutter inlet. 92 Figure 79. Different types of gutter. 92 Figure 80. Canal inlet. 92 Figure 81. Diagram of an example of sand filter. 93 Figure 82. Turn-down pipe inside pond outlet. 95 Figure 83. Composition of a monk. 96 Figure 84. Position of the monk in the pond. 97 Figure 85. Position of the monk according the downstream dike. 97 Figure 86. Wooden monk. Small and medium size. 98 Figure 87. Wooden pipe. 99 Figure 88. Mould of a monk. Front view; Upper view. 100 Figure 89. Monk. Upper view and example of size. 101 Figure 90. Functioning of a monk. 102 Figure 91. Concrete pipe. Croos cut; Mould; Final pipe. 103 Figure 92. Setting of a pipe overflow. 104 Figure 93. Type of setting basin. Natural; In concrete. 105 Figure 94. Setting basin. Normal; Improved. 106 Figure 95. Setting of a vegetable cover on the dikes. 106 Figure 96. Dikes with plants. Vegetable garden; Small animals; Trees. 107 Figure 97. Type of erosion and soil conservation. Streaming; Infiltration; Protection channel. 107 Figure 98. Fences. In scrubs; In wood or bamboo. 108 Figure 99. Schematic life cycle of a pond. 113 Subsistence fishfarming in Africa xIII
  14. 14. Figure 100. Setting of fish pond: 4. Fishfarming. 114 Figure 101. Trophic pyramids. 115 Figure 102. Differents algae. 115 Figure 103. Aquatic plants. 116 Figure 104. Rotifers. 116 Figure 105. Crustaceans. 116 Figure 106. Insects. 117 Figure 107. Molluscs. 117 Figure 108. Vertebrates other than fish. 118 Figure 109. Beneficial effects of organic fertilizers. 119 Figure 110. Preparation of dry compost. 123 Figure 111. Applying animal manures to a drained pond bottom. 125 Figure 112. Applying animal manures to water-filled ponds that have been stocked (I). 125 Figure 113. Applying animal manures to water-filled ponds that have been stocked (II). 125 Figure 114. Preparation of an anaerobic compost. 125 Figure 115. Compost heap in crib in a pond. 126 Figure 116. Setting of fish pond: 4. Fishfarming and 5. End of cycle. 128 Figure 117. Diagram of a seine. 129 Figure 118. The differents steps to construct a simple seine. 130 Figure 119. Setting of the pole to hold the seine. 130 Figure 120. Construction of a central-bag seine. 131 Figure 121. Manipulation of a seine. 131 Figure 122. Gill nets. 133 Figure 123. Use of a cast net. 134 Figure 124. Different types of dip nets. 135 Figure 125. Differents types of local traps. 135 Figure 126. Fish packing in plastic bags. 138 Figure 127. Sexual differentiation of differents species. 140 Figure 128. Fingerlings produced per fish density in Oreochromis niloticus. 141 Figure 129. Fingerlings produced per females body weight in Oreochromis niloticus. 141 Figure 130. Hapas and cages. 142 Figure 131. Differents systems of reproduction of tilapia in hapas and cages. 143 Figure 132. Live fish storage in hapas or nets. 144 Figure 133. Diagram on the relationships between the stocking density, the instant growth rate (G) and the instant yield per surface unit (Y) with and without complementary feeding. 146 Figure 134. Yield and average weight of Oreochromis niloticus at the harvest in function of initial density. 147 Figure 135. Impact of the presence of a predator (here, Hemichromis fasciatus) in fishponds. 148 Figure 136. Measurement gears. 149 Figure 137. Length - Weight relationships. 150 Figure 138. Harvest of the fish. 151 Figure 139. Examples of way to collect the fish outside of the pond. 152 Figure 140. Setting of fish pond: 5. End of cycle and start again… 154 Figure 141. Fish piping on surface; Dead fish floating on surface. 156 Figure 142. Diseases of fish. Bacterial diseases; External parasites. 156 Figure 143. Example of life cycles of fish disease factors. 157 Figure 144. Structures to facilitate the feeding. 161 Figure 145. Some predators of fish. 164 Figure 146. Differents methods of natural drying of fish. 166 Figure 147. Example of smoking method of fish. 166 Figure 148. Example of salting system. 166 Figure 149. Mosquito and snail. 172 Figure 150. Several human behavior to avoid nearby the ponds. 172 Figure 151. Cleaning of the dikes. 172 xiv Subsistence fishfarming in Africa
  15. 15. APPENDIx 187 Figure 152. Principal terms pertinent to the external morphology of a fish. 207 Figure 153. Different body shapes. 207 Figure 154. Cross-section of body. 208 Figure 155. Jaws. 208 Figure 156. Tooth shapes. 209 Figure 157. Fontanellae. 209 Figure 158. Barbels. 210 Figure 159. Gill slits without opercule; gill arch formed by ceratobranchial, gill rakers, hypobranchial and epibranchial, gill filaments; external gill. 210 Figure 160. Accessory aerial breathing organs. 211 Figure 161. Pair fins. 211 Figure 162. Dorsal fin. 212 Figure 163. Caudal fin. 212 Figure 164. Different types of scales. 213 Figure 165. Lateral line. 213 Figure 166. Location of electric organs. 213 Figure 167. Principal measurements that may be taken on a fish. 215 Figure 168. External features of the Cichlidae. 216 Figure 169. Courtship and spawning in a substrate spawner Cichlidae, Tilapia zillii. 218 Figure 170. Nest of Oreochromis niloticus; Oreochromis macrochir. 219 Figure 171. Courtship and spawning in a mouthbrooder Cichlidae, Haplochromis burtoni from Lake Tanga- nyika. 220 Figure 172. Mouthbrooding. 220 Figure 173. Example of the life cycle of a maternal mouthbrooding tilapia. 221 Figure 174. Different stages in mouthbrooders. 222 Figure 175. Comparison between fry of substrate spawners and mouthbrooders. 222 Figure 176. Relationship the weight of fish of 20 cm and the size of maturation for Oreochromis niloticus for several geographic location. 224 Figure 177. Size class of Oreochromis niloticus according several geographic location. 224 Figure 178. Comparison of growth rate for different species in natural field by locality. 225 Figure 179. Comparison of growth rate for different species in natural field by species. 225 Figure 180. Relative Fecundity (% of total weight), % of hatching (% total eggs) of Clarias gariepinus, monthly average rainfall and average temperature. Brazzaville. 227 Figure 181. Courtship in Clarias gariepinus. 228 Figure 182. First stages of development for Clarias gariepinus. 229 Figure 183. Several stages of larval development until 17 days. Clarias gariepinus; Heterobranchus longifi- lis. 229 Figure 184. Compared growth of several African fish species. 230 Figure 185. Growth of Heterotis niloticus and of Lates niloticus. 238 Figure 186. The ichthyoregions and the countries. 245 Subsistence fishfarming in Africa xV
  16. 16. LIST OF TABLES Part I - INTRODUCTION AND THEORICAL ASPECTS 1 Table I. World fisheries and aquaculture production and utilization, excluding China (FAO, 2007). 4 Table II. Origin and number of fish species introductions in Africa. 10 Table III. Introduced species with a negative ecological effect recorded. 11 Table IV. Different levels of intensification of fishfarming systems 16 Table V. Characteristics of the two main models of farming towards the various factors of production. 17 Part II - PRACTICAL ASPECTS 27 Table VI. Color of the soil and drainage conditions of the soil. 50 Table VII. Topographical features for ponds. 54 Table VIII. Advantages and disadvantages of the barrage and diversion ponds. 63 Table IX. Differents shape of a pond of 100 m2. 66 Table X. Size of fattening ponds. 68 Table XI. Resource availability and pond size. 68 Table XII. Characteristics of shallow and deep ponds. 69 Table XIII. Diversion structures to control stream water levels. 78 Table XIV. Channel dimensions. 80 Table XV. Examples fo dimension of dikes. 86 Table XVI. Expression of values of slope according the chosen unit. 87 Table XVII. Informations on the dimensions of the monk according the size of the pond. 100 Table XVIII. Estimation of the discharge and draining duration of the pond according the diameter of the outlet. 101 Table XIX. Inside dimensions of the monk according the diameter of the pipe. 101 Table XX. Examples of necessary time for building of ponds (man/day). 110 Table XXI. Approximate output on the works of excavation made by hand. 110 Table XXII. Example of calendar of works to do for the construction of a pond (workers of 400 men per day). 111 Table XXIII. Example of calendar according the seasons (15 ponds) in Cameroon. 111 Table XXIV. Maximum amount of fresh solid manure per day in 100 m2 pond. 120 Table XXV. Quantity to spread per type of manure. 120 Table XXVI. Organic fertilizers commonly used in small-scale fish farming. 121 Table XXVII. Particular characteristics of composting methods. 122 Table XXVIII. Production of Oreochromis niloticus in function of the number of breeders in a pond of 4 ares – 122 farming days. 141 Table XXIX. Levels of various nutrients in different species of fish. 158 Table XXX. Relative value of major feedstuffs as supplementary feed for fish. 159 Table XXXI. Example of formula for tilapia and catfish farming. 160 Table XXXII. Example of quantity of food to give according time per m2 of pond. 160 Table XXXIII. Feeding rate for tilapia in pond related to the size (table of Marek). 160 Table XXXIV. Examples of stop feeding per species in function of the temperature 161 Table XXXV. Monitoring. x: following; xx: fuller check or major repair; V: In drained pond only. 162 Table XXXVI. Examples of management for 4 ponds. Harvest after 3 months; After 4 months. 169 Table XXXVII. Useful life of fish farm structures and equipment (in years, assuming correct utilization) 170 xvi Subsistence fishfarming in Africa
  17. 17. APPENDIx 187 Table XXXVIII. The tonnage of halieutic products in 2005 per African countries (FAO, 2006). 194 Table XXXIX. The checklist of freshwater species which have been the subject of an introduction in Africa (FAO, 2006; Fishbase, 2006). 195 Table XL. List of species introduced by African countries. 197 Table XLI. List of freshwater fish used in aquaculture by country (FAO, 2006; Fishbase, 2008). 203 Table XLII. Diet of several species of tilapia in natural waters. 217 Table XLIII. Size at sexual maturation, maximale size and longevity of different species of tilapia. 223 Table XLIV. Some characteristics of African countries. 240 Table XLV. Characteristics of ichthyoregions and lakes in Africa. 244 Table XLVI. The ichthyoregions and their repartition by country in Africa. 246 Table XLVII. The genera and species of tilapias recorded by countries. 248 LIST OF SPECIES FILE File I. Cichlidae. - Oreochromis andersoni 256 File II. Cichlidae. - Oreochromis aureus 257 File III. Cichlidae. - Oreochromis esculentus 258 File IV. Cichlidae. - Oreochromis macrochir 259 File V. Cichlidae. - Oreochromis mossambicus 260 File VI. Cichlidae. - Oreochromis niloticus 261 File VII. Cichlidae. - Oreochromis shiranus 262 File VIII. Cichlidae. - Sarotherodon galileus 263 File IX. Cichlidae. - Sarotherodon melanotheron 264 File X. Cichlidae. - Tilapia guineensis 265 File XI. Cichlidae. - Tilapia mariae 266 File XII. Cichlidae. - Tilapia rendalli 267 File XIII. Cichlidae. - Tilapia zillii 268 File XIV. Cichlidae. - Hemichromis elongatus and Hemichromis fasciatus 269 File XV. Cichlidae. - Serranochromis angusticeps 270 File XVI. Cichlidae. - Serranochromis robustus 271 File XVII. Clariidae. - Clarias gariepinus 272 File XVIII. Clariidae. - Heterobranchus longifilis 273 File XIX. Arapaimidae. - Heterotis niloticus 274 Subsistence fishfarming in Africa xVII
  18. 18. LIST OF PHOTOS Part I - INTRODUCTION AND THEORICAL ASPECTS 1 Part II - PRACTICAL ASPECTS 27 Photo A. Measurement of a slope (DRC) [© Y. Fermon]. 56 Photo B. Example of rectangular ponds in construction laying in parallel (Liberia) [© Y. Fermon]. 68 Photo C. Cleaning of the site. Tree remaining nearby a pond {To avoid}(DRC); Sites before cleaning (Liberia) [© Y. Fermon]. 77 Photo D. Channel during the digging (Liberia) [© Y. Fermon]. 80 Photo E. Stakes during the building of the dikes (Liberia) [© Y. Fermon]. 82 Photo F. Dikes. Slope badly made, destroed by erosion (DRC)[© Y. Fermon]; Construction (Ivory Coast) [© APDRA-F](CIRAD). 89 Photo G. Example of non efficient screen at the inlet of a pond (Liberia) [© Y. Fermon]. 93 Photo H. Example of filters set at the inlet of a pond in Liberia [© Y. Fermon]. 93 Photo I. Mould and monks (Guinea). The first floor and the mould; Setting of the secund floor [© APDRA-F] (CIRAD). 100 Photo J. First floor of the monk associated with the pipe (Guinea) [© APDRA-F](CIRAD). 102 Photo K. Top of a monk (DRC)[© Y. Fermon]. 102 Photo L. Building of a pipe(Guinea) [© APDRA-F](CIRAD). 103 Photo M. Setting of a fences with branches (Liberia) [© Y. Fermon]. 108 Photo N. Compost heap. [Liberia © Y. Fermon], [© APDRA-F](CIRAD). 126 Photo O. Use of small beach seine (Liberia, Guinea, DRC) [© Y. Fermon]. 132 Photo P. Mounting, repair and use of gill nets (Kenya, Tanzania) [© Y. Fermon]. 132 Photo Q. Cast net throwing (Kenya, Ghana) [© F. Naneix, © Y. Fermon]. 134 Photo R. Dip net (Guinea) [© Y. Fermon]. 135 Photo S. Traps. Traditionnal trap (Liberia); Grid trap full of tilapia (Ehiopia) [© Y. Fermon]. 136 Photo T. Fish packing in plastic bags (Guinea, (Ehiopia) [© Y. Fermon, © É. Bezault]. 138 Photo U. Hapas in ponds (Ghana) [© É. Bezault]. 143 Photo V. Concrete basins and aquariums (Ghana) [© Y. Fermon]. 145 APPENDIx 187 Photo W. Nests of Tilapia zillii (Liberia) [© Y. Fermon]. 219 Photo X. Claroteidae. Chrysichthys nigrodigitatus [© Planet Catfish]; C. maurus [© Teigler - Fishbase]; Auchenoglanididae. Auchenoglanis occidentalis [© Planet Catfish]. 232 Photo Y. Schilbeidae. Schilbe intermedius [© Luc De Vos]. 233 Photo Z. Mochokidae. Synodontis batensoda [© Mody - Fishbase]; Synodontis schall [© Payne - Fishbase]. 234 Photo AA. Cyprinidae. Barbus altianalis; Labeo victorianus [© Luc De Vos, © FAO (drawings)]. 235 Photo AB. Citharinidae. Citharinus gibbosus; C. citharus [© Luc De Vos]. 235 Photo AC. Distichodontidae. Distichodus rostratus; D. sexfasciatus [© Fishbase]. 236 Photo AD. Channidae. Parachanna obscura (DRC) [© Y. Fermon]. 236 Photo AE. Latidae. Lates niloticus [© Luc De Vos]. 237 xviii Subsistence fishfarming in Africa
  19. 19. Part I INTRODUCTION AND THEORICAL ASPECTS Contents • Fishfarming: Aim and issues • Type of fishfarming • Biogeography and fish species • Summary Subsistence fishfarming in Africa 1
  20. 20. CONTENTS - PART I Chapter 01 - FISHFARMING: AIM AND ISSUES 3 I. WHY? 3 II. PRESSURE ON THE RESOURCES 6 II.1. Modifications of the habitat 6 II.2. Water pollution 8 II.3. Fisheries impact 9 II.4. Introductions 9 III. INTERNATIONAL ASPECTS 12 IV. OBJECTIVE OF FISHFARMING 13 Chapter 02 - TYPE OF FISHFARMING 15 I. VARIOUS TYPES OF FISHFARMING 15 II. SOME HISTORY… 17 III. A FISHFARMING OF SUBSISTENCE: GOAL AND PRINCIPLE 17 IV. POLYCULTURE VS MONOCULTURE 18 Chapter 03 - BIOGEOGRAPHY AND FISH SPECIES 21 I. GEOGRAPHY 21 II. THE SPECIES 21 I.1. The Cichlidae 22 II.2. The Siluriformes or catfishes 23 II.3. The Cyprinidae 23 II.4. Other families and species 24 SUMMARY 25 Cover photo: Ö Children fishing fingerlings in river for the ponds, Liberia, ASUR, 2006 - © Yves Fermon 2 Subsistence fishfarming in Africa
  21. 21. Chapter 01 FISHFARMING: AIM AND ISSUES I. WHY? Fisheries and aquaculture contribute to the food security primarily in three ways: Ö To increase the food availabilities, Ö To provide highly nutritive animal proteins and important trace elements, Ö To offer employment and incomes which people use to buy of other food products. A little more than 100 million tons of fish are consumed worldwide each year, and ensure to 2.5 billion of human at least 20% their average needs per capita of animal proteins (Figure 1 below). This can range to over 50% in the developing countries. In some of the zones most affected by food insecurity - in Asia and Africa, for example - the fish proteins are essential because, they guarantee a good part of the already low level of needs of animal proteins. Approximately 97% of the fishermen live in the developing countries, where fishing is extremely important. Fish production in Africa has stagnated over the past decade, and availability of fish per capita decrease (8.8 kg in the 90s, about 7.8 kg in 2001) (Table I, p. 4). Africa is the only continent where this tendency is observed, and the problem is that there do not exist other sources of proteins accessible to all. For a continent where food security is so precarious, the situation is alarming. Even if Africa has the lowest consumption of fish per capita in the world, the marine and inland water ecosystems are very productive and sustain important fisheries which recorded a rise in some countries. With a production of 7.5 million tons in 2003 and similar levels in previous years, the fish ensures 50% or more of the animal protein contributions of many Africans - i.e. the second rank after Asia. Even in sub-Saharan Africa, the fish ensures nearly 19% of the animal protein contribu- tions of the population. This constitutes an important contribution in an area afflicted by hunger and malnutrition. But whereas the levels of production of fishings are stabilized, the population continues to grow. With the sight of the forecasts of UN on the population trends and the evaluations available on the Millions tonnes 140 China 120 World excluding China 100 80 60 40 20 0 50 55 60 65 70 75 80 85 90 95 00 04 Years Figure 1. World capture and aquaculture production (FAO, 2007). Subsistence fishfarming in Africa 3
  22. 22. Table I. World fisheries and aquaculture production and utilization, excluding China (FAO, 2007). 2000 2001 2002 2003 2004 2005 Production (million tonnes) Inland Capture 6.6 6.7 6.5 6.6 6.8 7.0 Aquaculture 6.0 6.5 7.0 7.6 8.3 8.8 Total 12.6 13.3 13.5 14.2 15.1 15.8 Marine Capture 72.0 69.8 70.2 67.2 71.3 69.7 Aquaculture 4.9 5.3 5.6 6.1 6.6 6.6 Total 76.9 75.2 75.8 73.3 77.9 76.3 Total Capture 78.6 76.6 76.7 73.8 78.1 76.7 Aquaculture 10.9 11.9 12.6 13.8 14.9 15.4 Total 89.5 88.4 89.3 87.5 93.0 92.1 Utilization Human consumption 63.9 65.7 65.7 67.5 68.9 69.0 Non-food uses 25.7 22.7 23.7 20.1 24.0 23.1 Population (billions) 4.8 4.9 5.0 5.0 5.1 5.1 Per capita food fish supply (kg) 13.3 13.4 13.3 13.4 13.5 13.4 future tendencies of halieutic production, only to maintain the fish consumption per capita of Africa on his current levels, the production should increase of more than one third during the 15 next years, which is a challenge. The situation was partly aggravated by the significant increase in exports, and harvests of non-African fleets operating in the area under the fisheries agreements. Fish coastal resources are already heavily exploited and marine capture fisheries would be diffi- cult to produce more, even through massive investments. Difficult to reduce exports, considering the need for foreign currencies in the countries concerned. After a slight downturn in 2002, the total world catch in inland waters is again increase in 2003 and 2004 to reach 9.2 million tonnes during the past year. As previously, Africa and Asia represent approximately 90 percent of the world total and their respective shares are relatively stable (Figure 2, p. 5). The fisheries, however, seem in crisis in Europe where the total catch has dropped by 30% since 1999. Game fishing represents a substantial part of the catch. The statistics of developed countries on catches in inland waters, published by FAO, are generally based on information provi- ded by national correspondents, and the total catch may vary significantly depending on whether they take into account or not catch of game fisheries. In Africa - as in the world in general - aquaculture will play an important role. Globally, aqua- culture accounts for about 30% of world supplies of fish. The aquacultural production in Africa ac- counts for only 1.2% of the world total (Figure 3, p. 5). The aquaculture in Africa today is primarily an activity of subsistence, secondary and part-time, taking place in small-scale farmings. This African production primarily consists of tilapia (15 000 T), of catfishes (Clarias) (10 000 T) and of common carps (5 000 T). It is thus about a still embryonic activity and which looks for its way from the point of view of the development for approximately half a century. The aquaculture yet only contributes most marginally to the proteins supply of water origin of the African continent where the total halieutic production (maritime and inland) was evaluated in 1989 to 5.000.000 T. The part of fish in the proteins supply is there nevertheless very high (23.1%), slightly less than in Asia (between 25.2 and 29.3%), but far ahead of North America (6.5%) or Western Europe (9.4%), world mean of 4 Subsistence fishfarming in Africa
  23. 23. Oceania 0.2% North and Central America 2.0% Europe 3.5% South America 4.9% Africa 24.7% Asia 64.8% Figure 2. Inland capture fisheries by continent in 2004 (FAO, 2007). 16.5% (Figure 4, p. 6). Aquaculture in Africa thus remains limited. There are several reasons for this, but the most impor- tant is that the sector is not treated as a business enterprise, in a viable and profitable point of view. Quantity Asia (excluding China)  Western Europe 3.54% and the Pacific  21.92% Latin America and the Caribbean 2.26% North America 1.27% 8.51% Near East and North Africa 0.86% China 69.57% Central and Eastern Europe 0.42% Sub-Saharan Africa 0.16% Value Asia (excluding China)  and the Pacific  29.30% Western Europe 7.72% Latin America and the Caribbean 7.47% North America 1.86% 19.50% Near East and North Africa 1.19% China 51.20% Central and Eastern Europe 0.91% Sub-Saharan Africa 0.36% Figure 3. Aquaculture production by regional grouping in 2004 (FAO, 2007). Subsistence fishfarming in Africa 5
  24. 24. Fishery food supply (kg/capita) 30 Aquaculture 25 Capture 20 15 10 5 0 70 79 88 97 04 70 79 88 97 04 70 79 88 97 04 World China World excluding China Years Figure 4. Relative contribution of aquaculture and capture fisheries to food fish consumption (FAO, 2007). But this does not mean ignoring the need for fisheries management. Better management of ma- rine and inland fisheries in Africa contribute to the safeguarding of these important sectors of food production. Aquaculture is not intended to replace fishery but to supplement the intake of animal protein. II. PRESSURE ON THE RESOURCES The continental aquatic environments are particularly affected by the human activities: modifica- tion or disappearance of the habitats generally resulting from water development (dams), pollution of various origins, overexploitation due to fishing as well as the voluntary or not introductions of non- native species. The consequences, amplified at the present time by the increase in population and an increasingly strong pressure on the natural resources, endanger fish fauna quite everywhere in the world. Long enough saved, Africa suffers in its turn these impacts, even if pollution for example, remains still relatively limited in space. II.1. MODIFICATIONS OF THE HABITAT The alteration of habitat is one of the most important threats to aquatic life. The changes that may have two distinct origins which generally interfere nevertheless: 9 Climate change with its impact on water balance and hydrological functioning of hydrosys- tems; 9 The changes due to man both in the aquatic environment and its catchment area. II.1.1. CLIMATE CHANGES The existence of the surface aquatic environments depends closely on the contributions due to the rains, and thus on the climate. Any change in climate will have major consequences in terms of water balance that will lead by example by extending or reducing aquatic habitat. A spectacular event is the Lake Chad area of which strongly decreased during the 1970s due to a period of dryness in the Sahel. We know that the climate has never been stable on a geological and aquatic environments have always fluctuated without that man can be held responsible (the phenomenon «El Niño» for example). But we also know that man can act indirectly on the climate, either locally by deforestation, or at global level by the emission of certain gases in the «greenhouse effect». These last years, world opinion has been alerted to a possible warming of the planet which would be due to the increase in air content of carbon dioxide, methane and chlorofluorocarbons (CFCs), whose emission mass is 6 Subsistence fishfarming in Africa
  25. 25. linked to industrial activities. If it is not clear to what extent and how fast will this warming, it may be feared that these climate changes occur in the coming decades, resulting in a change in rainfall in some regions of the world. Besides small predictable consequences on the water (increase or de- crease in local rainfall), we can also expect an increase in sunshine and temperature, changes in the distribution of vegetation, at an elevation sea levels. Although it is still impossible at the local level to assess the consequences of the changes announced, it seems clear, whatever the magnitude of the phenomenon that aquatic fauna as a whole will be the first affected.. II.1.2. DEVELOPMENTS The various uses of water for agriculture, energy production, transport, domestic needs, are at the base of many hydrological building facilities. These constraints affect the water balance but also, directly or indirectly, the aquatic habitats. ■ Dams Large hydroelectric dams are expensive constructions, whose economic interest is often contro- versial and whose environmental impact is important. When we block a stream to create a dam, we provoke numerous modifications of the environ- mental habitat and the fish community and we disrupt the movements of migratory fishes. ■ Development of rivers The development facilities with the construction of dykes, the rectification of water course, the construction of locks for navigation ... are still limited in Africa, but we can nevertheless give some examples of projects that have changed quite considerably natural systems. In the valley of Senegal, for example, many work was completed for better managing the water resources of the river and to use them at agricultural ends. The purpose of the construction of a dam downstream nearby the estuary (dam Diama) is to prevent the coming back of marine water in the lower course of the river during the dry season, whereas the dam Manantali located upstream makes it possible to store great quantities of water at the time of the overflood and to restore them according to the request to irrigate vast perimeters. All the water resources of the valley of Senegal is now partially under control, but the water management becomes complex to deal with sometimes conflict demands in term of uses. ■ Reduction of floods plains and wetlands The wetlands are often considered as fertile areas favourable for agriculture. Everywhere in the world the development projects and in particular the construction of dams had an significant impact on the hydrosystems by reducing sometimes considerably the surface of the floodplains which are places favourable for the development of juveniles of many fish species.. ■ Changes in land use of the catchment area The quantity and the quality of the contributions out of surface water to aquatic ecosystems depend on the nature of the catchment area and its vegetation. However the disappearance of the forests, for example, whether to make of them arable lands or for the exploitation of wood for do- mestic or commercial uses, has, as an immediate consequence, an increase of the soil erosion and water turbidity, as well as a modification of the hydrological mode with shorter but more brutal runoff resulting from a more important streaming. The problem of the deforestation concerns Africa in general and the available information shows that the phenomenon is worrying by its scale. Thus, it was discovered in Madagascar that the defo- restation rate was 110 000 ha per year for 35 years, and erosion rate of 250 tonnes of soil per hectare have been reported. In the Lake Tanganyika drainage, deforestation is massive too. The erosion on the slopes has resulted in significant contributions to the lake sediment and changes in wildlife in some coastal areas particularly vulnerable. If current trends continue, the figures are coming with an estimated worrying that at this rate, 70% of forests in West Africa, 95% of those from East Africa and 30% of the congolese coverage would have to disappear by the year 2040. The increase in the suspended solid in water, and silt deposits in lakes and rivers, has many ef- fects on aquatic life. There are, of course, reduce the transparency of its waters with implications for the planktonic and benthic photosynthesis. The suspension elements may seal the branchial system of fish or cause irritation and muddy deposits deteriorate the quality of substrates in breeding areas. Subsistence fishfarming in Africa 7
  26. 26. II.2. WATER POLLUTION If water pollution has long appeared as a somewhat secondary phenomenon in Africa, it is clear that it is increasingly apparent in recent years. In general, however, lack of data and more detailed information on the extent of water pollution in Africa. II.2.1. EUTROPHICATION OF WATER The nutritive elements (phosphates, nitrates) are in general present in limited quantities in the aquatic environments, and constitute what one calls limiting factors. Any additional contribution of these elements is quickly assimilated and stimulates the primary production. When the natural cycle is disturbed by the human activities, in particular by the contributions in manure, detergents, waste water in general, excesses of phosphates (and to a lesser extent of nitrates) is responsible for the phenomenon of eutrophication. This phenomenon results in an excessive proliferation of algae and/ or macrophytes, and a reduction in the water transparency. The decomposition of this abundant organic matter consumes much oxygen and generally leads to massive mortalities of animal species per asphyxiation. Eutrophication also has as a result to involve strong variations of the dissolved oxygen concentration and pH during the day. In the lakes, the phenomenon of “bloom” (the “fleur d’eau” of the French speaking) is one of the manifestations of eutrophication. Eutrophication of Lake Victoria during the last 25 years is fairly well documented. Increased intakes of nutrients to the lake is the result of increasing human activities in the catchment area of the lake: increased urbanization, use of fertilizers and pesticides for the crops, use of pesticides for control of tsetse flies ... II.2.2. PESTICIDES In the second half of the twentieth century the use of chemical pesticides has become wides- pread in Africa, as elsewhere in the world to fight against both the vectors of major diseases and pests of crops. The range of products used is very large and, if some have a low toxicity towards aquatic organisms, many are xenobiotics, ie substances that have toxic properties, even if they are present in the environment at very low concentrations. This is particularly true for pyrethroids (permethrin, deltamethrin) but especially for organochlorines (DDT, dieldrin, endrin, endosulfan, ma- lathion, lindane), which, in addition to their toxicities have important time remanence, this which accentuates their accumulation and thus their concentration in food webs. II.2.3. HEAVY METALS Under the term of “heavy metals”, one generally includes several families of substances: 9 Heavy metals in the strict sense, with high atomic mass and high toxicity, whose presence in small amounts is not necessary to life: cadmium, mercury, lead… 9 Metals lower atomic mass, essential for life (trace elements), but quickly become toxic when their concentration increases: copper, zinc, molybdenum, manganese, cobalt… Heavy metals usually occur at very low concentrations in natural ecosystems but human activi- ties are a major source of pollution. Heavy metals come from the agricultural land and water systems by intentional inputs of trace elements and pesticides, discharge from refineries or factories treating non-ferrous metals (nickel, copper, zinc, lead, chromium, cadmium ...), discharges from tanneries (cadmium, chromium) or paper pulp (mercury). It must be added the impact of atmospheric pollution related to human activities (including industrial), and domestic and urban effluents (zinc, copper, lead). Mercury pollution may have originated in industrial uses (paper industry), the exploitation of gold deposits, the use of organomercury fungicides. The problems associated with heavy metal contamination resulting from the fact that they accumulate in the organisms where they may reach toxic levels. II.2.4. BIO-ACCUMULATION An alarming phenomenon with certain contaminants, including heavy metals or pesticides, is the problem of bioaccumulation which leads to the accumulation of a toxic substance in an organism, sometimes in concentrations much higher than those observed in the natural environment. This concerns various contaminants. 8 Subsistence fishfarming in Africa
  27. 27. Organisms with concentrated pollutants can enter to turn the trophic chain, and if the product is not degraded or removed, it will concentrate more and more with each trophic chain link, eg from algae to ichthyophagous birds. This phenomenon which is called biomagnification, shows that the pollution of environment by substances that are measured in very small quantities in water, can have unexpected consequences on higher consumer. II.3. FISHERIES IMPACT The impact of fishing on fish populations appears primarily, according to the fishing gears used, by a selective pressure on certain species, either on adults, or on juveniles. It is frequently thought that fishing alone, when used with traditional gear, can not be held responsible for the disappearance of fish species. Indeed, it is not easily conceivable that one can completely eliminate a population by captures made as a blind man contrary with what can occur for hunting. However, a pressure associated with changes in habitat can lead fairly rapidly declining species. The effects of fishing are particularly sensitive to large species with low reproductive capacity. One quotes for example the quasi-disappearance of the catfish Arius gigas in the basin of Niger. In this species, the male is buccal incubator of a few large eggs. In the early 20th century, it referred to the capture of specimens of 2 meters long, while since 1950 the species seemed to become very rare. One of the clearest fishing effect is showned in the population demography, with the reduction in the mean size of species and the disappearance of large individuals. Indeed, if the fishery usually starts with large gear mesh, the size of these decreases as catches of large individuals are rare. In some cases, the mesh size is so small that gear catch immature individuals and populations of species that can not reproduce collapsing dramatically. In the lake Malombe for example, the fishing of Oreochromis (O. karongae, O. squamipinnis) was done with gillnets. It has been observed in the 1980s increased fishing with small mesh seines, and a parallel collapse of the Oreochromis fishery. This mode of exploitation would be responsible also for the disappearance of nine endemic species of large size of Cichlidae. II.4. INTRODUCTIONS While for centuries introductions of fish species have been promoted across the world to improve fish production, they have become in recent decades the subject of controversy among scientists and managers of aquatic environments. Indeed, the introduction of new species can have significant effects on indigenous fish populations. The introduction of new species in an ecosystem is sometimes the cause of the phenomena of competition that may lead to the elimination of native species or introduced species. But there may also have indirect changes, which are generally less easy to observe, through the trophic chains. To correctly interpret the impacts of introductions, it is necessary to distinguish several levels from intervention: 9 That of the transplantation of species of a point to another of the same catchment area; 9 That of the introduction of alien species to the basin but coming from the same biogeogra- phic zone; 9 That of the introduction of species coming from different biogeographic zones, even from different continents. II.4.1. COMPETITION WITH THE INDIGENOUS SPECIES Introduced species may compete with native species, and possibly eliminate them. This is es- pecially true when introducing predator species. One of the most spectacular cases is that of the introduction into Lake Victoria of the Nile Perch, Lates niloticus, a piscivorous fish being able to reach more than 100 kg. To some scientists, this predator is the cause of the decline and likely extinction of several species belonging to a rich endemic fauna of small Cichlidae which he fed on. ` Subsistence fishfarming in Africa 9
  28. 28. II.4.2. EFFECT ON AQUATIC ECOSYSTEM The introduction of a predator in an aquatic ecosystem can affect the biological functioning of the system through the trophic chains. Using the example of Lake Victoria, the Nile perch would be responsible for the virtual disappearance in the 80s of the group of detritivores / phytoplanctivore of haplochromine (Cichlidae endemic), and the group zooplanctivores which were respectively 40 and 16% of the biomass of demersal fish. Detritivorous have been replaced by indigenous shrimp Cari- dina nilotica, and by the zooplanctivores Cyprinidae pelagic Rastrineobola argentea, these latter two species have become the mean food of the Nile perch after the disappearance of the haplochromine. II.4.3. HYBRIDIZATIONS The introduction into the same water body of related species that do not normally live together may result in hybridization. Species of tilapia, in particular, are known to hybridize, which can cause genetic changes for the species surviving. For example, in Lake Naivasha, Oreochromis spilurus in- troduced in 1925 was abundant in the years 1950 and 1960, and then hybridize with O. leucostictus introduced in 1956. This resulted in the disappearance of O. spilurus and hybrids. The disappea- rance of the species O. esculentus and O. variabilis, endemic to Lakes Victoria and Kyoga, could be due to hybridization and/or competition with introduced species (O. niloticus, T. zillii). Hybrids O. niloticus x O. variabilis were found in Lake Victoria. If we consider the introductions and movements of fish in Africa, everything and anything has been done (Annexe 02, p. 197, Table II, p. 10 and Table III, p. 11). First by the colonialists who introduced the species they used as trout or carp. Then many species have been transplanted from country to country in Africa to test for fishfarming, as many tilapia. This up to nonsense as to bring strains of Nile Tilapia (Oreochromis niloticus niloticus) or Mossambic Tilapia (O. mossambicus) in areas where there were native strains. For example, the famous strain of “Bouaké” in Ivory Coast which would be, in fact, a mixt of several broodstocks, was introduced into several countries in which the species O. niloticus is native. Same thing on the strain of Butaré, in Rwanda, where it would seem that it is a stock brought back the first time to the United States by a research institute and brought back afterwards to Rwanda!! (Lazard, pers. com.). Elements are given on the distribution of the species in Appendix 05, p. 255. Ö In this case, it is to pay attention to the provenance of the fish to use and watershed where action is taken, more so, because of the risks incurred by the introduction of fish and national and international legislative aspects concerning biodiversity.. Ö This is not because a species has already been introduced in the intervention area, that it is necessary to use it. Table II. Origin and number of fish species introductions in Africa. Coming from Number Africa 206 North America 41 South America 3 Asia 58 Europe 92 Unknown 128 Total 528 10 Subsistence fishfarming in Africa

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