Ecologie et Répartition Spatiale des Peuplements des Siluriformes dans deux Rivières Forestières Yoko et Biaro (Province Tshopo, Fleuve Congo, R.D. Congo)

La présente étude sur l’écologie et la répartition des Siluriformes entreprise de septembre 2008 à août 2009, a pour but de caractériser et de déterminer les facteurs responsables de la distribution spatio-temporelle des Siluriformes dans les rivières Yoko et Biaro dans la Réserve forestière de Yoko. Des filets maillants, palangres et nasses traditionnelles ont été utilisés pour capturer les poissons. Ainsi, 572 silures au total, repartis en 15 espèces appartenant à 9 genres et 6 familles ont été récoltés. Les Clariidae et Claroteidae sont les plus diversifiées avec respectivement : 5 et 4 espèces chacune. L’indice de diversité de Shannon varie de 1,54 à 0,40 ; tandis que, celui de Simpson oscille entre 0,75 et 0,18 et l’équitabilité entre 0,86 et 0,29. Ce qui indique une biodiversité élevée mais dont l’équilibre et la structure varient selon les stations. L’Analyse en Composantes Principales (ACP), l’Analyse Factorielle des Correspondances (AFC) et l’Analyse Canonique des Correspondances (ACC) montrent qu’il existe, d’une part, des liens entre les stations Yoko 1, 2, 3 et 4 et Biaro 3 et d’autre part, entre les espèces Schilbe marmoratus, Clarias (Anguilloclarias) ebriensis, Schilbenigrita, Clarias buthupogon, Clarias pachynema et Parauchenoglanis punctatus, du fait de la corrélation positive qui existe entre les paramètres abiotiques et la végétation ripicole. De même, Schilbe grenfelli ; Anaspidoglanis macrostoma et Chrysichthys (Melanodactylus) dageti sont respectivement liées aux stations Biaro 1, 2 et 4, du fait de la corrélation positive existant avec les variables végétation ripicole, température de l’eau élevée (avoisinant 24°C), vitesse de l’eau moyennement faible (variant entre 0,29 et 0,37 m/s) d’une part et d’autre part, du fait de plus grande profondeur de l’eau (0,67 m), plus grande largeur de rivière (17,9 m) et oxygène dissous légèrement déficitaire. Et enfin, du fait de la nature des substrats (sablonneux, caillouteux, rocheux garni de pierres, feuilles mortes, bois morts et débris végétaux). Ceci atteste, que les variables environnementales (abiotiques et biotiques) agissent ensemble dans la répartition spatiale des peuplements des Siluriformes.   This paper on the ecology and distribution of Siluriformes, undertaken from September 2008 to August 2009, focuses on characterizing and determining the factors responsible for the spatio-temporal distribution of Siluriformes in the Yoko and Biaro rivers in the Yoko Forest Reserve. Gillnets, longlines, and traditional traps were used to catch the fish. 572 catfish in total, divided into 15 species, belonging to 9 genera and 6 families were collected. The Clariidae and Claroteidae are the most diversified with 5 and 4 species each respectively. Shannon's diversity index varies from 1.54 to 0.40, while that of Simpson oscillates between 0.75 and 0.18 and the equitability between 0.86 and 0.29. This indicates a high biodiversity but their balance and structure varies according to the stations. Principal Component Analysis (PCA), Factorial Correspondence Analysis (FCA), and Canonical Correspondence Analysis (CCA) show that there are, on the one hand, links between stations Yoko 1, 2, 3 and 4 and Biaro 3 and, on the other hand, between the species Schilbe marmoratus, Clarias (Anguilloclarias) ebriensis, Schilbe nigrita, Clarias buthupogon, Clarias pachynema and Parauchenoglanis punctatus. This is due to a positive correlation that exists between the abiotic parameters and the riparian vegetation. Likewise, Schilbe grenfelli, Anaspidoglanis macrostoma, and Chrysichthys (Melanodactylus) dageti are respectively linked to Biaro stations 1, 2, and 4. This also is due to the positive correlation existing with the variables riparian vegetation, high water temperature (around 24°C), and speed of moderately low water (varying between 0.29 and 0.37 m/s) on the one hand. On the other hand, it is due to greater water depth (0.67 m), greater river width (17.9 m), slightly lower dissolved oxygen, and finally because of the nature of the substrates (sandy, stony, rocky topped with stones, dead leaves, dead wood and plant debris). This shows that the environmental variables (abiotic and biotic) act together in the spatial distribution of Siluriformes populations

Physico-Chemical Factors of Lubilanji River (Oriental Kasaï Province, Democratic Republic of the Congo)

Background and aim: Fishing and fi sh farming sectors currently face major challenges related to the lack of knowledge of data on the physico-chemical quality of water bodies from Lubilanji River. This investigation intended to determine the physico-chemical parameters of Lubilanji River.Methods: Fourteen physico-chemical parameters were studied in Lubilanji River including temperature, turbidity, transparency, conductivity, pH, alkalimetric title, total hardness, calcium, nitrate, phosphate, oxygen dissolved, depth, width and velocity.Results: The analysis showed that average value of transparency in all stations is of 54.09 cm with coefficient of variation of 31.84%. While the average of water velocity is 91.30 m/s with coefficient of variation of 49.80% in all stations. The parameters like water velocity, turbidity, temperature, calcium and pH indicated their low infl uence on stations. According to the results found, the Libilanji River should be rich in ichthyological biodiversity.</p

Mollusk communities of the central Congo River shaped by combined effects of barriers, environmental gradients, and species dispersal

Rapids, falls, and cascades might act as barriers for freshwater species, determining the species community up- and downstream of barriers. However, they affect community composition not only by acting as barriers but also by their influence on environmental gradients. Moreover, the directional dispersal of species along the watercourse might determine community composition. A suitable system to study these differential effects is the Congo River, the world’s second largest river by discharge. The small ‘Upper Congo Rapids’ ecoregion features several rapids known as barrier for fishes. The Wagenia Cataracts at the town of Kisangani constitute the strongest drop of the Congo River and several studies have emphasized its role as barrier for fish distribution. Alternative explanations for this pattern, however, are rarely evaluated. Though mollusks represent a vital component of the macrozoobenthos, with distribution patterns and underlying drivers often distinct from that of fishes, virtually no field surveys of the Congo River have been reported for decades. We collected and determined mollusks of 51 stations, recorded environmental conditions, and generated proxies for directional species dispersal and an indirect barrier effect. Those variables were subjected to distance-based redundancy analyses and variation partitioning in order to test whether the mollusk community compositions are better explained by an individual or combined influence of the direct and indirect effect of the cataract barrier, environmental conditions, and downstream-directed dispersal. Our survey showed an exclusive upstream/downstream distribution for just four out of the 19 species, suggesting a limited barrier effect. We revealed no direct influence of the barrier itself on community composition but of substrate type. However, we found an indirect effect of the barrier through replacing spatially structured communities upstream of the cataract with more uniform ones downstream. Downstream‑directed dispersal explained the highest fraction of variation in mollusk communities. Thus, environmental factors, the indirect cataract effect, and downstream-directed spatial proxies model mollusk community composition in concert. These results support previous studies showing a multi-factorial imprint on communities. However, a large fraction of variation community composition remained unexplained, potentially due to flood plain dynamics that (re-)shape mollusk communities constantly and a high temporal turnover, evidenced by the comparison with historical surveys. This is likely caused by the growth of Kisangani and resulting human activities. A monitoring system could allow better assessments of these impacts on communities and the conservation status of endemic species in the Wagenia Cataracts.</p

Diet and breeding biology of Stomatorhinus corneti Boulanger, 1899 (Pisces, Mormyridae)

Cette étude de la biologie d’un Mormyridae peu connu, Stomatorhinus corneti Boulanger, 1899, a été réalisée dans les rivières forestières Yoko et Biaro du bassin du Congo, région de Kisangani. Diverses techniques de pêche ont permis de récolter 144 spécimens de S. corneti. L’analyse des contenus stomacaux (135 estomacs) a permis d’identifier 19 catégories de proies appartenant aux groupes: débris animaux, débris végétaux, insectes, crustacés, œufs et nymphes d’insectes. Le coefficient intestinal (LI-/LS) moyen calculé pour les spécimens de S. corneti est de 0,56 ; ce qui nous permet de classer cette espèce parmi les invertivores. Le régime alimentaire général de cette espèce, exprimé en pourcentage d’occurrence corrigé, montre que les individus des deux sexes utilisent les mêmes types de proie en proportions semblables. L’espèce S. corneti se reproduit en avril et en septembre. La taille de première maturité est de 80 mm de longueur totale. Le nombre moyen d’ovocytes est de 538 pour une longueur totale de 80 mm en moyenne et pour un poids moyen des gonades de 0,8 g. La taille des ovocytes varie de 0,4 à 1,5 mm de diamètre.This study of the biology of a little known Mormyridae, Stomatorhinus corneti Boulanger, 1899, was carried out in the forest rivers Yoko and Biaro of the basin of the Congo River, Kisangani region. Various fishing techniques have raised 144 specimens of S. corneti. Average Intestinal (LI/LS) coefficient calculated for specimens of S. corneti was 0.56; this allowed us to classify this species among the invertivores. The analysis of stomach contents (135 stomachs) helped identify 19 categories of prey belonging to the groups: animal remains, plant remains, insects, crustaceans, eggs and nymphs. The general diet of this species expressed as a fixed percentage of occurrence shows that individuals of both sexes use the same types of prey in similar proportions. The species S. corneti breeds in April and September. The first maturity size is 80 mm total length. The average number of oocytes is 538 for a total length of 80 mm on average and a weight average of gonads of 0.8 g. The size of the eggs varies from 0.4 to 1.5 mm in diameter

Régime alimentaire et biologie de la reproduction de Stomatorhinus corneti Boulanger, 1899 (Pisces, Mormyridae)

Diet and breeding biology of Stomatorhinus corneti Boulanger, 1899 (Pisces, Mormyridae). This study of the biology of a little known Mormyridae, Stomatorhinus corneti Boulanger, 1899, was carried out in the forest rivers Yoko and Biaro of the basin of the Congo River, Kisangani region. Various fishing techniques have raised 144 specimens of S. corneti. Average Intestinal (LI/LS) coefficient calculated for specimens of S. corneti was 0.56 ; this allowed us to classify this species among the invertivores. The analysis of stomach contents (135 stomachs) helped identify 19 categories of prey belonging to the groups : animal remains, plant remains, insects, crustaceans, eggs and nymphs. The general diet of this species expressed as a fixed percentage of occurrence shows that individuals of both sexes use the same types of prey in similar proportions. The species S. corneti breeds in April and September. The first maturity size is 80 mm total length. The average number of oocytes is 538 for a total length of 80 mm on average and a weight average of gonads of 0.8 g. The size of the eggs varies from 0.4 to 1.5 mm in diameter.Cette étude de la biologie d’un Mormyridae peu connu, Stomatorhinus corneti Boulanger, 1899, a été réalisée dans les rivières forestières Yoko et Biaro du bassin du Congo, région de Kisangani. Diverses techniques de pêche ont permis de récolter 144 spécimens de S. corneti. L’analyse des contenus stomacaux (135 estomacs) a permis d’identifier 19 catégories de proies appartenant aux groupes : débris animaux, débris végétaux, insectes, crustacés, œufs et nymphes d’insectes. Le coefficient intestinal (LI-/LS) moyen calculé pour les spécimens de S. corneti est de 0,56 ; ce qui nous permet de classer cette espèce parmi les invertivores. Le régime alimentaire général de cette espèce, exprimé en pourcentage d’occurrence corrigé, montre que les individus des deux sexes utilisent les mêmes types de proie en proportions semblables. L’espèce S. corneti se reproduit en avril et en septembre. La taille de première maturité est de 80 mm de longueur totale. Le nombre moyen d’ovocytes est de 538 pour une longueur totale de 80 mm en moyenne et pour un poids moyen des gonades de 0,8 g. La taille des ovocytes varie de 0,4 à 1,5 mm de diamètre.Mahamba Byanikiro Richard, Kankonda Busanga Alidor, Ndjaki Nsila Jacob, Micha Jean-Claude. Régime alimentaire et biologie de la reproduction de Stomatorhinus corneti Boulanger, 1899 (Pisces, Mormyridae). In: Revue d'Écologie (La Terre et La Vie), tome 72, n°2, 2017. pp. 177-191

Preliminary Data on Biology of Stomathorinus Cf Polli Matthes, 1964 of Masendula Stream (Kisangani, RD Congo)

Background and aim: Stomatorhinus cf polli, one of species of Mormyridae whose flesh is highly appreciated by local communities. Unfortunately, there is very little information about biology and ecology of Stomatorhinus cf polli. This study aimed to determine the ecology and biology of Stomathorinus cf polli.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Methods: The circular dip scoop net of 0.5 mm of mesh and the amplifier were used during twelve months. 260 specimens of Mormyridae were collected in a single site of Masendula stream. All fish samples were weighed using scales, as well as each fish were measured using a tape measure and caliper. Diet and reproduction were analyzed. &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;&nbsp;Results: The analysis of 151 stomach contents of Stomatorhinus cf polli allowed identifying three prey categories (animal detritus, vegetable detritus and chironomidae). The diet of Stomatorhinus cf polli expressed in the coefficient of occurrence showed that individuals feed the same prey but in different proportions. The mean intestinal coefficient calculated for specimens of Stomatorhinus cf polli is 0.58. This species prefers more to consume animal detritus. For reproduction, the findings showed that this species breeds throughout the year. The mean relative fecundity is 25,125 oocytes per kg.</p