Doses efficaces en glyphosate et en 2,4-D pour le contrôle chimique des laitue d'eau (Pistia stratiotes, Linn.) et toxicité du glyphosate vis-à-vis des tilapias (Sarotherodon melanotheron)

The toxic effects of two herbicides Round up (gliphosate) and 2,4-D (herbazol) were tested on Pistia stratiotes (Linn. Araceae) samples cultivated in glass aquariums. The gliphosate appears to be more toxic on Pistia Stratiotes than 2,4-D. It was then tested on tilapia Sarotherodon melanotheron juveniles. The lethal dose for tilapia (CL50 = 13.25 mg.l -1) is about 18, 37 and 74 times higher than the glyphosate toxic dose for plants at 1, 2 and 4 meters water depth respectively.

Écologie de bassins de lagunage pour le traitement d'effluents domestiques en milieu tropical humide (Côte d'Ivoire)

The waste water treatment of Dabou (Côte d'Ivoire), made of three oxydation ponds (B1, B2 and B3), is designed to ensure a biological treatment of domestic sewage and a valorization of the final effluent in aquaculture. In order to understand the ecological mechanisms and the performance of this system, a pluridisciplinary program was achieved in February 1989.

Importance de certaines caractéristiques biologiques dans la structuration génétique des espèces de poissons: le cas de Ethmalosa fimbriata et Sarotherodon melanotheron

Six populations of Ethmalosa fimbriata and six of Sarotherodon melanotheron have been analysed using enzymatic electrophoresis. The study of gene flow intensity in these two species indicate that: - In Ethmalosa fimbriata, a migratory species with high fecundity and pelagic eggs, there is a high gene flow between populations (3 Nm 83). - In Sarotherodon melanotheron, a sedentary and mouthbrooder species with low fecundity, there is a low gene flow between populations (1 Nm 4).

Toxicité de l'ammoniaque chez le silure africain Heterobranchus longifilis

The acute toxicity of ammonia to the African catfish (Heterobranchus longifilis, Valenciennes 1840) was studied using static bioassay systems.

Toxicité des sulfures dissous chez le poisson-chat africain, Heterobranchus longifilis (Valenciennes, 1840)

Biological tests were carried out using static bioassay systems to determine the median lethal concentration of total sulfide (H2S, HS, S2) for African catfish (Heterobranchus longifilis, Valenciennes, 1840) at fry and juvenile stages.

Étude quantitative de l'upwelling sur le plateau continental ivorien

A wind-driven upwelling occurs on the continental shelf of Ivory Coast during the northern summer months; by studying the average conditions in the wind field, it has been found that in steady state the vertical speed upwards does not exceed 70 cm per day. The vertical flow per km super(2) is estimated in 46 m super(3)/s for a channel 50 m depth and in 92m super(3)/s for a channel 300 m depth. This study does not include the inclination of isopycnes in geostrophic adjustment with the variations of the Guinea current.

Le régime alimentaire de Dentex angolensis, Poll et Maul, 1953 (Sparidae)

The food of Dentex angolensis, studied from 386 stomachs, consists essentially of small epibenthic crustaceans and, with less importance, of fishes. A systematic list with abundance and occurrence is given here. It is noted that the composition of the stomach content can differ with depth and season.

Étude du crabe rouge profond Geryon quinquedens en Côte d'Ivoire. 1 - Prospection le long du talus continental: résultats des pêches

From Aug 1975 to Jan 1976 a fishing survey for deep-sea red crab Geryon quinquedens was executed along the Ivorian coast between 3{degree} and 7{degree}30'W. Three regions could be distinguished: a central one with poor catches (1.6 kg/trap/20h); an east region with the best catches (5 kg/trap/20h); and a west region, also with good catches (4.5 kg/trap/20h). For the whole survey, catches only took place between 300 and 700m, the best at 400 m. A distinct sexual segregation was observed according to bathymetry with the percentage of males increasing with depth. Nearly the same abundance was observed in Côte d'Ivoire, in Congo and North Angola, while in South Angola catches are somewhat higher.

Excrétion organique du phytoplancton et activité bacterienne hétérotrophe dans le Dôme de Guinée (Océan Atlantique Tropical Est)

Primary production rates in the Gulf the Guinea (east tropical Atlantic) were measured with in situ incubations. The extracellular organic carbon passed through 0.8 u pore size membrane filters averaged 29.5% of the carbon fixed by photosynthesis. These is a good linear correlation (r=0.86) between assimilation and organic excretion. The significance and limits of the method for the measurements of low rates of photosynthesis is discussed. The influence of ecological factors (nutrients, light and stability) cannot be demonstrated. The importance of bacterial regeneration processes by reutilization of algal extracellular products is assessed.

Quelques observations sur la présence des Cumacés dans le zooplancton des eaux néritiques de Côte d'Ivoire

Cumacea were only observed in night plankton of the Côte d'Ivoire continental shelf. However they are not always observed and their occurrence seems to depend on the marine seasons. In September, December and April, the catches were very poor indeed, whereas May and June showed interesting results. Most of the species are rarely seen in the upper layer. Several activity rhythms could be shown for the most common species present in the hauls.

Copépodes pélagiques du plateau ivoirien. 2 - Utilisation de l'arbre de longueur minimum dans le classement des récoltes

The minimum spanning tree algorithm is used to classify two sets of planktonic copepod samples. This algorithm links the samples the distance of which is minimum, without doing a loop, so that the sum of the segment lengths is minimum. The authors estimated the distance between samples by 2 different ways: by a coefficient of association the Jaccard's index - and by the x2 distance. Jaccard's index is not retained but the use of the x2 distance allows comparison with the 'analyse factorielle des correspondances'. The results are discussed from an ecological point of view.

Note sur le régime alimentaire de quelques poissons démérsaux de Côte d'Ivoire

Stomach contents from 21 species of demersal fish caught on Grand Bassam (Côte d'Ivoire) fishing grounds at 20 and 35 m depth are analyzed. The results are compared with those of Longhurst (1957, 1960). The great importance of Crustacea in the food of those species appears clearly. A representative scheme of the diet is suggested.

Aspects principaux des variations du phytoplancton sur le plateau continental ivorien

21 surveys over the whole Ivorian continental shelf lead to a description of the phytoplankton repartition according to the different seasons: great and small cold seasons, discharge seasons, and warm seasons. Yearly means of surface cells concentrations range from 1000 to 30000 cells per liter, corresponding to a daily production of 386 to 1166 mg C/m2, according to regression analysis. These values make Côte d'Ivoire a rather rich region, which is subjected to wide standing crop variations.

Variation des bio-volumes des zooplancton du plateau continental entre le Cap des Palmes et le Cap des Trois Pointes

Three years of weekly sampling from a coastal station and 29 monthly cruises over the whole continental shelf were studied for zooplankton quantitative variation. Settled volumes were preferred to displacement volumes. At the coastal station, near Abidjan, a negative correlation was found between the log2 of zooplankton volume and the preceding fortnight temperature. On the whole shelf, the differences between the 6 considered areas were tested by the variance analysis. There were significative differences in shallow waters only (20 m). During the main cold season, the upwelling of Tabou causes a very important enrichment 30 to 60 nautical miles to the east. Eastwards the plankton drifts and decreases in abundance. The zooplankton maximum is not always inshore, but often in the middle of the shelf and sometimes over the slope. During the little cold season the enrichments caused by coastal upwelling are less abundant and restricted to smaller areas. During the warm season, the waters are uniformly poor. During the cold season, over the 60m depths, the zooplankton maximum lies between 10 and 20 m and seems to sink in deeper waters. In warm season the vertical repartition is rather homogeneous in the first 40 meters. The diel vertical migrations show a very consistent rhythm, varying with the season.

Estimation de la production zooplanctonique sur le plateau continental ivoirien

An attempt was made to calculate zooplankton production from weights and settled volumes and from the life cycle of some copepods. Biomass data were recorded during several years from 24 monthly cruises and from a coastal station sampled biweekly. Dry weight data were directly measured or were calculated from the settled volumes using a linear regression. They range, on an average, from 0.965 to 5.56 g m-2 day-1 from the shore line to the edge of the continental shelf. The mean life-span of the cohorts of 12 species of copepods is about 20 days. It is assumed that only 1 spawn occurs per generation-time and that the standing stock is turned-over during the life span of a cohort. The production ranges from 48.2 to 278 mg dry weight m-2 day-1 or 17.9 to 103 mg C m-2 day-1, according to the depth of the studied areas. One third of carnivorous production occurs among the copepods. So, it is assumed that the herbivorous and omnivorous production is about 2/3 of the total zooplanktonic production. This would be a more accurate estimate of secondary production. The standing stock of zooplankton and fishes are in the same order of magnitude; the ratio zooplanktonic production/total fishery is 0.8%.