Thermal stability and phytoplankton in Volta Lake,Ghana

The correlation between the thermal stability and phytoplankton was positive during the flood season when the transparency of water was the determining factor. On the other hand the correlation was negative during the dry season when the nutrient condition was the determining factor. The correlation was of no significance when these two contrasting seasonal phases were disregarded.     

Biology of the small pelagic fishes in the new Volta Lake in Ghana

Summary A number of small pelagic fish species were found in the new Volta Lake in Ghana. Three, the clupeids Cynothrissa mento and Pellonula afzeliusi, and the schilbeid Physailia pellucida, rapidly became dominant, and these together with another schilbeid Siluranodon auritus and the clupeid-like cyprinid Barilius niloticus are here considered.Pellonula and Physailia eat chiefly invertebrates; the former especially at the surface, the latter in mid-depths or at the bottom. Zooplankton is important to all sizes of Physailia, but only to juveniles of Pellonula. Barilius feeds almost entirely on adventitous forms taken at the surface and Siluranodon on algae and rotifers. Cynothrissa, the largest fish studied, feeds mainly on fish. The food range taken is thus wide, and differences in diet are discussed in terms of the probable future of each species in the new lake as it matures.This paper is taken from a thesis accepted for the M. Sc. Degree of the University of Dublin.     

Biology of the small pelagic fishes in the New Volta Lake in Ghana

Summary Five species of small pelagic fishes in the new Volta Lake in Ghana showed a die periodicity in catches, and were strongly attracted to light. As these forms occur typically in rivers, their school formation and migratory movements were investigated, and their purposes are discussed. It appears that a diel vertical movement occurs so that the fish can exploit a feeding ground at its richest moments, and at times when they are least conspicuous to predators. The school is the normal method of migrating, as it confers protection against predators. Once the fish cease to move, however, the school loses its coherence and its individuals disperse.Indirect evidence is also presented that in three species a longitudinal upstream migration may occur, probably to breed after the rains, and in two others, there may be a lateral movement into prevailing winds.Resume Dans le nouveau Lac Volta au Ghana, cinq espèces de petits poissons pélagiques montraient un periodicité quotidien dans les échantillons, et un phototropisme positive fort. Comme ces espèces se trouvent typiquement aux fleuves, les buts de comportement en banc et des movemments migratrices étaient étudiés. Il paraît que les poissons font un migration vertical diel pour exploiter leurs terrains de nourriture aux moments les plus riches, et quand ils sont les moins remarquables aux prédateurs. En banc, c'est le façon normale de migration, car il protège contre les carnassiers. Quand les poissons cessent leur migration, le banc perd son cohésion, et les poissons individuels dispersent.En trois espèces étudiées ici, l'évidence indirecte indique qu'ils font un migration en remontant le courant, probablement pour réproduire après les pluies, et dans les deux autres, un mouvement lateral au vent regnant.     

The bottom fauna of the rapids of the Black Volta River in Ghana

Summary The increase in abundance and biomass of the bottom fauna in the Black Volta River rapids seems to be closely related to increasing rate of water flow. These differences are due mainly to the increasing numbers of Cheumatopsyche larvae, a web spinning caddisfly. At higher current speeds more food is provided for this omnivorous species, and this seems to determine its density on the substratum. In a very slow current which prevents the use of webs for food catching, this genus is absent.The abundance and standing crop of bottom fauna at the end of dry season can be considered as the highest for the whole year. The presence of several instars of the commonest species guarantees almost continuous emergence and recolonization of the substratum during the dry season. With the onset of heavy rains and floods the communities found in the rapids are disturbed, and eventually completely destroyed. This is because the substrate is carried away by the swift flow of the river. Recolonization can be expected after the rains when the water level is low and the substratum again stabilized.The fauna of rapids is a community which can be expected to be almost completely destroyed when it becomes permanently flooded in any man-made lake. Some organisms, however, such as the larvae of Ecnomus and Cricotopus may establish themselves again in a habitat physically and chemically akin to that of rapids; such a habitat is for example the bark of flooded trees exposed to wave action and surrounded by water well saturated with oxygen.     

Functional morphology of the rat thyroid during the first months of the pubertal period

Morphofunctional parameters of the rat thyroid gland, at the light optic and electron microscopic levels, during first months of the pubertal period are not stable. Quantitative values of these parameters fluctuate with a period of 32-36 days. Some morphofunctional parameters, such as diameter of the thyrocyte nucleus and content of albumine-binding iodine in blood, depend on the animal's body mass, other parameters do not depend on it.     

Molybdenum supply of very low-birth-weight premature infants during the first months of life

This explorative study was performed to assess basic data on the Mo metabolism of premature infants. Premature (n=18, gestational age ≤32 wk, birth weight ≤1500 g) and healthy formula-fed term infants (n=14) were nourished and corrected for gestational age, identically. Plasma was collected at 3, 16, and 52 wk and 72 h balances were performed at 3 wk of age. In the premature infants, these investigations were preceded by two balance studies and an initial plasma collection. Increased Mo intake and low relative urinary excretion resulted in a retention of 4.4 (0.99–7.77) μg Mo/kg initially in premature infants (median, range). Parallel plasma concentrations were 5.5 (2.5–7.3) μg Mo/L, declining to 2.36 (0.73–3.87) μg Mo/L at 4 wk. Term infants rendered 1.49 (0.29–1.7) μg Mo/L (p<0.05), with no significant differences later. It was concluded that the supplementation of formulas for premature infants with Mo should be recinded until there is evidence for its necessity.     

Iron status of very-low-birth-weight infants during the first 15 months of infancy.

The adequacy of iron stores in infants of very low birth weight (defined as less than 1500 g) in Canada is unknown. We monitored the iron status of 81 such infants at 3, 6, 9, 12 and 15 months of age. All of the infants were fed formula fortified with iron (13 mg/L) for at least 6 months, starting at 2 months of age. The plasma ferritin level decreased after the formula was no longer used. Although 90% of the infants were given cereal fortified with iron (30 mg of iron per 100 g) by 9 months of age, the plasma ferritin level continued to decrease. The level was less than 10 micrograms/L in 54% of the infants at 12 months of age and in 74% at 15 months; this indicated depleted iron stores. Because of delayed development very-low-birth-weight infants eat small amounts of cereal and therefore require iron-fortified formula throughout infancy.     

Reactive changes in the heat-resistant muscle tissue of lake frogs during heat acclimation

A study was made of the effect of heat acclimation of animals on the individual changes in the muscle heat resistance in populations of Rana ridibunda belonging to European or Asiatic groups of the species. The relationship between the levels of heat resistance of muscle cells and the value of its changes are the same in the populations of these groups. It is believed that this relationship forms on the level higher than populational one.     

Prediction of the distribution of Glossina tachinoides (Diptera: Glossinidae) in the Volta basin of northern Ghana

The classification of a Landsat Thematic Mapper satellite image helped demonstrate prevailing habitat types and land use intensity in the Volta basin of the Northern Region of Ghana. A geo-referenced data layer comprising the capture results of a cross-sectional survey of Glossina tachinoides Westwood was over-laid on a data layer of habitat types within 500 m of either bank of the Volta river and its tributaries. An evaluation of the relationship between habitat types and the capture results of G. tachinoides suggested a strong preference of G. tachinoides for woodland, followed by shrubland, grassland and flood plains. The findings were used to classify the suitability of habitat types for G. tachinoides as 'high', 'medium' and 'low' and a prediction map for the distribution of G. tachinoides in the entire river network was produced. The usefulness of this method in estimating the potential distribution of G. tachinoides in an area of increasing agricultural expansion is discussed.     

Chemotherapy of Pseudomonas aeruginosa infections in children during the first three months of life]

The data on the efficacy of antibacterial drugs and their combinations in treatment of 150 three-month old infants with generalized infection due to Pseudomonas aeruginosa are presented. The clinical isolates of P. aeruginosa were found to be carriers of multiple drug resistance which markedly complicated the chemotherapy. Only combined antibacterial therapy of such infants proved to be rational. High activity of aminoglycosides, azlocillin and cefotaxime against P. aeruginosa and the synergistic action of their combinations observed in the patients permitted to recommend the use of combinations of the above drugs in the empirical chemotherapy.     

Fish and fisheries of the Muni lagoon in Ghana, West Africa

Muni is a closed lagoon that opens to the sea when the water level is high, especially during the rainy season. During the dry period, the water level is very low and the salinity of the lagoon water increases sometimes exceeding that of seawater. Only three finfish species and 8 shellfish species (live animals and empty shells) were found in the lagoon and surrounding wetlands during the study which was conducted in March–June 1994. The blackchin tilapia Sarotherodon melanotheron (Cichlidae) is the dominant species. The castnet is the most important fishing gear used in the lagoon followed by various finfish and shellfish traps. The fishing effort in the lagoon is high and, like catch rates, it was found to be inversely related to the volume of water in the lagoon and the fishing situation in the sea. The estimated exploitation level (E = 0.65) indicates that S. melanotheron in the Muni lagoon could be considered as over-exploited. From the gonadosomatic index, S. melanotheron appears to spawn continuously in the Muni lagoon between the months of March and June. The von Bertalanffy growth parameters were estimated for S. melanotheron as L = 12.5 cm standard length (SL), K = 0.70 yr^–1 and t₀ = 0.01 yr. The longevity of the fish is estimated as ca. 4.2 yr. Taboos and cultural practices contribute to the management and conservation of fisheries in the lagoon. However, additional formal management is required to ensure sustainability of the fisheries in the lagoon. In addition, there is a need to manage the lagoons physical and chemical environment including planting of mangroves around the lagoon in order to restore its mangrove cover. The poverty problem in the fishing community needs to be addressed to divert labour from the lagoon.     

Changes in the fish community of the Kpong Headpond, lower Volta River, Ghana after 25 years of impoundment

The Kpong Headpond was the second created on the Volta River after Akosombo Dam, primarily as a source of hydroelectric power generation and potable water supply, and additionally, it has supported some fish production in Ghana since impoundment. The changes in fish community of the Kpong Headpond were studied to provide baseline information for strategies formulation to support the socio-economic development of the reservoir. The study identified changes in the fish community of the reservoir by comparing occurrence, composition, relative abundance and relative importance estimates of fish species, families and trophic groups, from available previous studies in the reservoir. From the collated information all fishes identified in the reservoir were categorised based on occurrence and importance as disappeared, appeared, permanent, declined or important, to show current status. The results indicated that the fish community has experienced a shift in the composition and relative abundance of important species, families and trophic groups in terms of number and weight, while remaining ecologically balanced. Representatives of the families Osteoglossidae, Centropomidae and Characidae have declined while representatives of the families Claroteidae, Cyprinidae and Cichlidae have increased. The aufwuch-detritus and herbivores declined while semi-pelagic omnivores increased resulting in a shift in dominance to benthic and semi pelagic omnivores. The appearance of five species and the disappearance of 25 others indicated a dynamic restructuring of the fish community in the reservoir, as expected. Enforcement of fishing regulations including the use of appropriate gear and fishing methods, fishery access control, promotion of culture-based fisheries and improvement in fisher education are recommended topics for sustainable fisheries in the reservoir.     

Fish species found in the rocky sublittoral during winter months as revealed by the underwater application of the anaesthetic quinaldine

Using the anaesthetic quinaldine applied underwater, fish species not normally observed in the Scottish rocky sublittoral during the winter months have been recorded, and are listed.     

Influence of climatic factors on tree growth in riparian forests in the humid and dry savannas of the Volta basin,Ghana

Key message

The paper demonstrates the prospects and applications of dendrochronology for understanding climate change effects on riparian forests in the savanna landscape. 

Abstract

Riparian trees in savannas have a potential for dendro-climatic studies, but have been neglected hitherto. We examined ring-width series of Afzelia africana (evergreen) and Anogeissus leiocarpus (deciduous) to study the influence of climatic factors on the growth of riparian trees in the humid (HS) and dry (DS) savanna zones of the Volta basin in Ghana. A total of 31 stem discs belonging to A. africana and A. leiocarpus were selected from HS and DS to establish species-specific local chronologies of tree growth. Each individual of A. africana and A. leiocarpus from the two savanna sites showed distinct growth rings. Cross-dating of individual tree-ring patterns was successful using standard dendrochronological techniques. The mean annual growth rates of A. africana in the HS (1.38 ± 0.09) and DS (1.34 ± 0.08) were not statistically different. Furthermore, mean annual growth rate of A. leiocarpus in the DS (3.75 ± 0.27) was higher than in the HS (2.83 ± 0.16) suggesting that species in drier environment can have higher growth rates when sufficient soil moisture is available. The growth rates of both species at the same sites were different, which might indicate different water use strategies. High correlations of individual tree-ring series of A. africana and A. leiocarpus trees at HS and DS suggest a strong climatic forcing controlled by the seasonal movement of the inter-tropical convergence zone. The annual growth of A. africana and A. leiocarpus at both the HS and DS was significantly correlated with local temperature and precipitation. The negative correlations of the growth of the two tree species to global sea surface temperatures were however, indications that the growth of riparian forests can be impacted during El Niño-Southern Oscillation years. The result of our study shows that riparian trees in the humid and dry savanna zones of West Africa can be successfully used for dendrochronological studies.