Les Haplochromis spp. (Teleostei, Cichlidae) des zones rocheuses du Mwanza Gulf, lac Victoria, Tanzanie : structure des communautés et écomorphologie

L'ichtyofaune du lac Victoria est principalement composée d'espèces endémiques de Téléostéens appartenant à la famille des Cichlidés. La diversité des formes, observée chez ces poissons, en fait un des exemples les plus remarquables de radiation adaptative chez les vertébrés. Néanmoins, en raison du jeune âge (25 000 ans) de cet "essaim d'espèces", il est très difficile de séparer les espèces entre elles. En effet, la plasticité phénotypique de ces Cichlidés fait que les variations intraspécifiques peuvent être plus importantes que les variations interspécifiques. Dans le cadre d'un programme sur les Cichlidés pétricoles du Mwanza Gulf, en Tanzanie, nous avons étudié les structures des communautés de poissons des zones rocheuses selon différentes échelles spatiales afin d'apporter des éléments préliminaires à leur connaissance. A l'échelle du Mwanza Gulf, nous avons étudié les variations de la richesse spécifique. Nous avons pu mettre en évidence un effet "région". A l'échelle d'une station rocheuse, nous avons étudié les variations morphologiques d'une espèce, #Halochromis nyererei$ Witte & Witte-Maas, 1985... Des analyses multivariées ont été utilisées pour caractériser les variations morphologiques... Ce travail de thèse a donc permis de mettre en évidence la complexité de la structure des communautés des Cichlidés pétricoles du Mwanza Gulf. L'étude écomorphologique à l'échelle d'une population a démontré la plasticité écologique et phénotypique au sein d'une même espèce. Cette plasticité est probablement à la base de "l'essaim d'espèces" de Cichlidés observé dans le lac Victoria... (D'après résumé d'auteur

Spatial and temporal variation in population genetic structure of wild Nile tilapia (Oreochromis niloticus) across Africa

<p>Abstract</p> <p>Background</p> <p>Reconstructing the evolutionary history of a species is challenging. It often depends not only on the past biogeographic and climatic events but also the contemporary and ecological factors, such as current connectivity and habitat heterogeneity. In fact, these factors might interact with each other and shape the current species distribution. However, to what extent the current population genetic structure reflects the past and the contemporary factors is largely unknown. Here we investigated spatio-temporal genetic structures of Nile tilapia (<it>Oreochromis niloticus</it>) populations, across their natural distribution in Africa. While its large biogeographic distribution can cause genetic differentiation at the paleo-biogeographic scales, its restricted dispersal capacity might induce a strong genetic structure at micro-geographic scales.</p> <p>Results</p> <p>Using nine microsatellite loci and 350 samples from ten natural populations, we found the highest genetic differentiation among the three ichthyofaunal provinces and regions (Ethiopian, Nilotic and Sudano-Sahelian) (<it>R</it>_ST= 0.38 - 0.69). This result suggests the predominant effect of paleo-geographic events at macro-geographic scale. In addition, intermediate divergences were found between rivers and lakes within the regions, presumably reflecting relatively recent interruptions of gene flow between hydrographic basins (<it>R_ST</it>= 0.24 - 0.32). The lowest differentiations were observed among connected populations within a basin (<it>R_ST</it>= 0.015 in the Volta basin). Comparison of temporal sample series revealed subtle changes in the gene pools in a few generations (<it>F </it>= 0 - 0.053). The estimated effective population sizes were 23 - 143 and the estimated migration rate was moderate (m ~ 0.094 - 0.097) in the Volta populations.</p> <p>Conclusions</p> <p>This study revealed clear hierarchical patterns of the population genetic structuring of <it>O. niloticus </it>in Africa. The effects of paleo-geographic and climatic events were predominant at macro-geographic scale, and the significant effect of geographic connectivity was detected at micro-geographic scale. The estimated effective population size, the moderate level of dispersal and the rapid temporal change in genetic composition might reflect a potential effect of life history strategy on population dynamics. This hypothesis deserves further investigation. The dynamic pattern revealed at micro-geographic and temporal scales appears important from a genetic resource management as well as from a biodiversity conservation point of view.</p

Chapitre 14. Les poissons des grands lacs d’Afrique de l’Est

photo Haplochromis pyrrochephalus, un Cichlidae pélagique endémique du lac Victoria, dont les populations se sont trouvées réduites après les changements écologiques du lac. Le Rift africain est jalonné, tout le long de son parcours, de chapelets de lacs dont l’origine est liée à l’histoire géologique de cette grande cassure de l’écorce terrestre. L’intense activité volcanique a fait naître des centaines de lacs de cratère, en particulier dans le Rift occidental. Au fond des vallées structur..

Ethology

Ethology calls on a wide range of disciplines including genetics, physiology, ecology, developmental biology, and evolution to converge in an integrated view of the organism, its function, and its interactions with its physical system. Among the vertebrates, bird and mammal behaviour have been the subject of much investigation, whereas fish behaviour is still relatively unknown barring a few exceptions, in particular species that are popular with aquarium enthusiasts. The majority of studies on African fishes focus on two families, the Mormyridae because of their particular means of communication (electric signals), and the Cichlidae, owing to their economic importance and significance in evolutionary science with the “species flocks” in the African great lakes (see box, “History of the ethology of African fishes”; chapter Diversity of African fish: a heritage of evolution)

Synodontis ngouniensis, new species (Siluriformes: Mochokidae) from the Ngounié and Nyanga basins, Gabon and Republic of Congo

Synodontis ngouniensis, new species, is described. It is endemic to the Ngounie River (Ogooue River basin) and the Nyanga River basin. It is distinguished from all other Synodontis species of the Lower Guinea Ichthyofaunal Province by: a dorsal spine with a smooth anterior margin except for the presence of 1-4 feeble serrations on the distal part; a maxillary barbel witha smooth membrane, which is proximally at least as broad as the barbel thread and situated on the posterior basal two third of the barbel; 12-19 mandibular teeth; 10-13 gill rakers on the ceratobranchial of the first branchial arch; a triangular humeral process, and a striking colour pattern of black overall background colour with irregular whitish lines and dots

Fish communities in East African rift lakes

The Great Lakes of East Africa are unique systems in various ways. The region has been subject to much tectonic activity. Hence, some of the deepest lakes of the world can be found in the area, most of them stretched in a north-south direction in the western branch of the Rift Valley (figure 19.1). The elongated and deep lakes Tanganyika and Malawi, together with the saucer-shaped, relatively shallow Lake Victoria form the three largest freshwater bodies in the region. All three figure amongst the top ten largest lakes in the world in terms of surface and volume. Other large lakes in the region include Kivu, Edward (with George), Albert, Turkana, Mweru and Rukwa.However, what really makes these lakes unique is their biodiversity and especially their fishes. Nowhere else in the world can one find a larger number of fish species than in these lakes. Not only is the sheer number of species exceptional, but most of these fishes are also endemic to a certain lake. Remarkably, the largest compound of the fish fauna, over 95% for the three large lakes, belongs to only one family, the Cichlidae. These cichlids represent the largest radiation of vertebrates in the world. Hence these lakes are considered natural laboratories for the study of evolution and speciation

Morphological screening of carp

We propose a simple method to quantify the morphology of 2-3-year-old carps (Cyprinus carpio) which is related to their fillet yield. This method is based on the automated image analysis of the lateral projection of the fish (mask). Seven morphological measurements specifically related to fillet yield of carps were defined. The comparison between this method and the conventional quantification of fish shape, based on measurements of skeletal landmarks, increases the significance of this fitting. From the analysis of the morphometric data, we propose a profitable carp morphotype which is defined by four angles and two distances which quantify the shape of the head and the position of the caudal peduncle, respectively. The main characteristic of this morphotype is the absence of a large dorsal development, and the ventral position of the caudal peduncle

Richesse et particularités de l'ichtyofaune du Marais de Kaw (Guyane française)

International audienc

Fish fauna in and around the Rapids of Mboungou Badouma and Doumé Ramsar site, Gabon

We assessed the fish diversity of the Ogooué and Sébé rivers in and around the Rapids of Mboungou Badouma and Doumé Ramsar site in Gabon. The ichthyofauna of this region has not been extensively sampled in over 150 years, yet encompasses one the most important type localities for fishes in Central Africa. We sampled a total of 31 sites and collected nearly 3000 fish specimens representing 97 species. Nine species appeared to be new to science, and one catalyzed the recent description of a new genus of mormyrid fishes

Onchocerciasis Control Programme in West Africa: a 20-year monitoring of fish assemblages

Onchocerciasis is a widespread disease in intertropical Africa, which, ultimately, causes irreversible blindness. The disease is transmitted by a small blackfly, Simulium damnosum (Diptera), which has aquatic larval and pupal stages. The breeding sites of the blackflies are riffles. These river reaches are the targets of the control campaign of the Onchocerciasis Control Programme in West Africa (OCP). An aquatic monitoring network covering the totality of the area exposed to the insecticide was set up to evaluate environmental impact. In this paper, we present results from the OCP 20-year period of monitoring of the ichthyofauna regularly exposed to larvicides. We do not record any measurable effects of pesticides on the CPUE, abundance of species, trophic structure, community structure or fish health. However, we detect the emergence of a number of medium-term tendencies. These tendencies may relate to climatic conditions that have a consequent effect on hydrology. Thus, we note a constant decrease in the CPUE from the beginning of the monitoring until 1995. The rivers were treated during that time until 1990 or 1993, depending on the station. But even after the treatments ended, the number of catches continued to decrease. As a result, we consider other factors to be the cause of that decline. The average level of annual discharges in this region has been decreasing regularly from the beginning of the 1970s. The production of fish fluctuates in all the rivers according to the flood rate. Important floods inundate larger areas, making greater quantifies of food available, and thus improving the conditions for reproduction. The determining factor of the ichthyological stock abundance seems to depend both on the extern and the duration of the flood. In our catches, the observed effect was not immediately evident but appeared a few years later as a cumulative effect of poor hydrological conditions. An increase in the CPUE since 1996 has been related to improved hydrological conditions. In these last few years, we have observed an intensification of the basic flow leading to a ground water renewal. Furthermore, on three of the stations investigated, it appeared that the impediment of rivers (dams) could induce different and/or antagonistic effects. In some cases, we have observed that in spite of unfavourable hydrological conditions, certain species appear to be favoured by the presence of the dam. But, the damming of the river has a negative effect on other species, particularly on the coefficient of condition of migratory fishes. The impact of these factors is enhanced by the fact they exist conjointly. © 1999 Ifremer/Cnrs/Inra/Ird/Cemagref/Éditions scientifiques et médicales Elsevier SASRésumé — Maladie largement répandue en Afrique intertropicale l’onchocercose est un fléau qui provoque, à son stade ultime, une cécité irréversible. La maladie est transmise par un petit Diptère, Simulium damnosum, qui présente une phase larvaire et nymphale aquatique. Ce sont les gîtes larvaires de ce vecteur, biefs à courant rapide des rivières, que le Programme de lutte contre l’onchocercose en Afrique de l’Ouest (OCP: Onchocerciasis Control Programme in West Africa) traite lors de ses campagnes de lutte. Comme toute lutte insecticide, OCP représentait une menace importante pour l’environnement. C’est pourquoi le programme s’est doté d’un réseau de surveillance des écosystèmes aquatiques, couvrant l’ensemble de la zone exposée aux épandages d’insecticides. Ce sont les résultats de vingt années de surveillance de l’ichtyofaune, régulièrement exposée aux traitements larvicides, qui sont présentés ici. Les différentes variables étudiées dans cette étude, ne permettent pas de mettre en évidence un effet décelable des pesticides sur la structure et la richesse spécifique des peuplements. De même, la composition trophique ou la santé des poissons ne semblent pas affectées. Cependant, nous observons parfois certaines tendances, à moyen terme, qui semblent être essentiellement sous l’influence des conditions climatiques, probablement hydrologiques. Ainsi, nous observons une diminution régulière des prises par unité d’effort (PUE) du début de la surveillance jusque vers 1995. Durant cette période, les rivières ont été, selon les stations, traitées jusque 1990 ou 1993. Mais, alors que les traitements étaient terminés, la diminution des captures s’est poursuivie. Nous pouvons donc estimer que d’autres facteurs en sont la cause. Si nous considérons les crues moyennes annuelles et régionales, nous observons une diminution régulière depuis le début des années 1970. Dans toutes les rivières, la production de poisson fluctue en fonction du régime d’inondation. Lorsque les crues sont favorables, elles inondent des superficies plus grandes, ce qui favorise la disponibilité en nourriture, et améliore donc les conditions pour la pérennité des espèces. En fait, le facteur déterminant de la production halieutique semble être lié à la fois à l’étendue et à la durabilité de l’inondation. Dans nos captures, l'effet apparaît avec quelques années de retard comme s’il y avait eu un effet cumulatif des mauvaises conditions hydrologiques. Inversement, l’accroissement des PUE depuis 1996 paraît bien corrélé aux meilleures conditions de crue observées. Ces dernières années, nous notons un renforcement de l’écoulement de base qui se traduit par une recharge des nappes phréatiques. Enfin, sur trois stations étudiées, les barrages peuvent induite différents effets, antagonistes ou non. Dans certains cas, nous observons qu’en dépit de mauvaises conditions hydrologiques, certaines espèces semblent être favorisées par le barrage et sa retenue d’eau. Inversement, le barrage du fleuve peut avoir un effet négatif sur certaines autres espèces, particulièrement sur celles qui effectuent des migrations longitudinales. Tous ces facteurs semblent montrer une pression d’autant plus importante qu’ils se produisent en synergie. © 1999 Ifremer/Cnrs/Inra/Ird/Cemagref/Éditions scientifiques et médicales Elsevier SA