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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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
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
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. 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. 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. 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. 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. 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. 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. 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
