Influence of nutrient concentrations on the seasonal abundance and distribution of Cyanophyceae in the coastal region of Mount Cameroon

Water management in the coastal region of Mount Cameroon is threatened by extensive and persistent noxious blooms of Cyanophyceae (blue-green algae) in the surface and near-surface mesotrophic and eutrophic zones. Nutrient concentrations and species composition of Cyanophyceae were investigated from surface waters at 15 stations from three sites along the Mount Cameroon region (Mudeka Creek, Tito Creek and Idenau Beach) during the rainy season, from July to August 1999, and during the dry season, from February to March 2000. Nitrate concentrations were extremely high during the rainy season, ranging from 240.07mg l–1 to 927.07mg l–1, and comparatively low, ranging from 1.79mg l–1 to 10.39mg l–1, during the dry season The Cyanophyceae community consisted of six genera: Microcystis, Lyngbya, Gloeocapsa, Trichodesmium, Chamaesiphon and Aphanocapsa. Three species (T. dispersa, T. lacustre and L. birgei) were present during the rainy season whereas five species, with two dominant (M. aeruginosa, G. dispersa), were present during the dry season. There was a positive correlation (r = 0.73) between nutrient concentration and Cyanophyceae concentration. Water transparency depth (Secchi disc depth) was much shallower during the rainy season than during the dry season, most likely as a result of the increased leaching of insoluble material from the land and decay of Cyanophyceae blooms during the rainy season. Management strategies to limit the formation of algal blooms in the region are discussed.Keywords: algal bloom, blue-green algae, Cameroon coast, Cyanophyceae, nutrientsAfrican Journal of Marine Science 2006, 28(1): 25–3

Detailed analysis of the food of Sarotherodon melanotheron(RUPPELL) from an inland tropical lake, Ibadan,Nigeria

No Abstract

Preliminary study on the domestication of broodstock of an ornamental aquarium fish, Synodontis obesus (Teleostei: Mochokidae) in concrete tanks

The state of ornamental aquarium fish export trade in Cameroon is largely undeveloped. This is due mainly to lack of technical know-how concerning domestication and breeding. Synodontis obesus broodfish has been domesticated for six months in concrete tanks located at Buea, Cameroon using local food materials and plankton species, without fertilization. The broodfish were domesticated under temperatures ranging from 20.4-24°C, pH, (6.6-10.0); dissolved oxygen, (0.75-11.0mg/l) and electrical conductivity, (40.5-523 µS/cm) in the experimental concrete tanks. Dissolved oxygen concentration was enhanced using an air blower. The average rate of aeration was 3.6 hours per day using an automatic timing device. The results also revealed that the levels of dissolved oxygen concentration were higher between the hours of 1200 and 1700 (5.2-6.0mg/l) even without aeration. Primary productivity was considerably increased by the aeration of the tanks at 3.6 h day-1. Brood fish were fed a mixture of 375g of tapioca, 100g of crushed boiled cabbage and 150g of crushed dried crayfish. The broodstock of this ornamental aquarium fish species may not survive in concrete tanks without the right type and quantity of supplementary food. Keywords: ornamental, aquarium, experimental tanks, broodstock, Synodontis obesus, domestication Tropical Freshwater Biology 2003/2004 Vol. 12/13: 137-15

Effects of Replacing Fishmeal with Soyabean in Diets of Oreochromis Niloticus Fingerlings in Buea, Cameroon

Oreochromis niloticus fingerlings were fed four with isoproteic (30% crude protein) diets in which soya bean meal (SBM) partially or completely replaced fishmeal (FM), and the effect of the diets on the growth performance and nutrient utilization of the fingerlings was evaluated. 80 fingerlings of mean weight 5.594g were distributed among 8 transparent plastic tanks (10/tank) with two replicates per treatment and the trial lasted 56 days. The control (Diet I) had no replacement of FM with SBM while the experimental diets: Diet II, Diet III and Diet IV had 35%, 65% and 100% replacement respectively. There were significant differences in the mean total weight gain at P<0.05, with fingerlings fed Diet III having the greatest mean total weight gain (3.695±0.061 g) and those in Diet II, the least (0.930±0.388g). The total percentage weight gain and the apparent protein efficiency ratio followed the same trend. Diet III was the most palatable diet with the greatest mean final feed intake value (1.853±0.004g). Percentage digestibility and feed conversion efficiency values of diets also increased with increasing replacement of FM. The effective substitution of 65% fishmeal by soya bean without negative effects on fish condition has positive implications for increased fish production in Cameroon from aquaculture.Des alevins Oreochromis niloticus ont été nourris sur base de quatre régimes isoprotéiques (30% de protéine brute) dans lesquels la farine de soja (FS) a partiellement ou totalement remplacé la farine de poisson (FP) ; et l’effet de ces régimes sur la croissance et l’utilisation des éléments nutritifs par les alevins a été évalué. Quatre-vingt (80) alevins d’un poids moyen de 5,594g ont été répartis dans 8 cuves en plastique transparentes (10/cuve) avec deux répétitions par traitement, et l’essai a duré 56 jours. Dans le régime témoin (régime I), il n’a pas eu de remplacement de farine de poisson par la farine de soja, tandis que les régimes expérimentaux - régimes II, III et IV ont respectivement eu des remplacements de 35%, 65% et 100%. On a noté des différences significatives au niveau du gain pondéral total moyen à P <0,05, les alevins nourris au régime III ayant le plus grand gain pondéral total moyen (3,695 ± 0,061 g) et ceux du régime II ayant le plus faible gain pondéral total moyen (0,930 ± 0.388g). Le pourcentage total du gain pondéral et le coefficient d’efficacité protéique apparente ont suivi la même tendance. Le régime III était le plus agréable au goût, avec la plus grande valeur moyenne d’absorption alimentaire finale (1,853 ± 0.004g). Les valeurs de pourcentage, de digestibilité et d’efficacité de conversion des aliments des régimes ont également augmenté parallèlement au remplacement croissant de la farine de poisson. La substitution efficace de 65% de la farine de poisson par la farine de soja, sans effets négatifs sur l’état des poissons, a des implications positives pour l’augmentation de la production de poissons au Cameroun.Mots-clés: Farine de poisson; Farine de soja; Régimes; Oreochromis niloticus; Camerou

Occurrence and Deleterious Effects of Algal Blooms Associated With Some Pollutants in Three Man-Made Lakes

Associations of plankton genera, some of which are known to be potentially harmful and indicative of pollution stress in surface waters were studied alongside some of their corresponding physico-chemical parameters, in three man-made lakes (reservoirs) over a period of 18 months in Ibadan, Nigeria. These lakes receive sewage effluents and agricultural run-offs. Two of these, Lakes Awba and Main are sites of drinking water abstraction. Bloom-forming algal families found in association included members of the phytoplankton class Chlorophyceae: (Pediastrium spp and Spirogyra spp.), the Bacillariophyceae which included Synedra, Melosira and Nitzschia species and potentially toxin-producing genera of the class Cyanophyceae (Microcystis, Anabaena, Aphanizomenon and Lyngbya). The plankton exhibited significant correlations with pH, temperature, total suspended solids, dissolved oxygen, carbon dioxide, nitrate-nitrogen and ammonium-nitrogen at various seasons of the year. An altered physico-chemistry of large areas of the lake and a total absence of aquatic life in some highly polluted parts were recorded in the study. Reports from lake users were recorded, of contaminated bad tasting water unfit to drink, unpalatable fish and skin infections, all indicators of the far-reaching effects algae can have on fresh water supplies. This paper calls for more frequent and thorough monitoring of such resources Keywords: Sewage, Bloom–forming algae, pollution, water quality parameters, agricultural run-offs, eutrophic, harmful algal bloomsTropical Freshwater Biology Vol. 17 (1) 2008: pp. 53-7

Metal Distribution and Bioaccumulation in Water and Fish of a Tropical Lake

A study was conducted to investigate the metal (copper, zinc and manganese) concentrations in the surface water and fish of a man-made lake receiving agricultural and domestic effluents in Ibadan, Nigeria. The lake (Main Lake, IITA) is a site of drinking water abstraction and the major water source for the surrounding agricultural research farms. Factor analysis indicated that copper was an important contributor to the total variance observed in the lake, being involved in Factor 1 of the 6-factor model. Significant differences occurred in the copper and manganese levels of the organs of Oreochromis niloticus at P< 0.05 and P< 0.01 respectively and in manganese levels of Sarotherodon. galilaeus at P< 0.05. Significant differences did not occur in Lates niloticus and Synodontis nigrita organs. Bioaccumulation factors from water to fish muscles were highest for manganese ranging from 4.56-10.56; zinc from 1.83-5.67 and copper from 1-1.8. These factors showed that despite the low levels of these metals in surface water, there may be an onset of bioaccumulation in some of the fishes. This work contributes to the baseline data on the presence and effects of metals in African freshwaters and could aid future plans for the control of toxic build-up in our aquatic environments. Keywords: Metal, concentrations, lake, bioaccumulation, water, fish and IITATropical Freshwater Biology Vol. 17 (1) 2008: pp. 81-9

Traditional use of indigenous mosquito-repellents to protect humans against mosquitoes and other insect bites in a rural community of Cameroon.

OBJECTIVE: To document and test the efficacy of indigenous traditional personal protection methods against mosquito bites and general nuisance. DESIGN: A prospective study based on a survey and field evaluation of selected plant-based personal protection methods against mosquito bites. SETTING: Bolifamba, a rural setting of the Mount Cameroon region. SUBJECTS: A structured questionnaire was administered to 179 respondents and two anti-mosquito measures were tested under field conditions. MAIN OUTCOME MEASURES: Identified traditional anti-mosquito methods used by indigenes of Bolifamba. Two plants tested under field conditions were found to be effective. RESULTS: Of the 179 respondents, 88 (49.16%) used traditional anti-mosquito methods; 57 (64.77%) used plant-based methods while 31 (35.2%) used various petroleum oils. The rest of the respondents, 91 (50.8%) used conventional personal protection methods. Reasons for using traditional methods were because they were available, affordable and lack of known more effective alternatives. The demerits of these methods were: labourious to implement, stain dresses, produce a lot of smoke/ repulsive odours when used; those of conventional methods were lack of adequate information about them, high cost and non-availability. When the two most frequently used plants, Saccharum officinarium and Ocimum basilicum were evaluated under field conditions, each gave a better protection than the control. CONCLUSION: Most plants used against mosquitoes in the area are known potent mosquito repellents but others identified in the study warrant further research. The two tested under field conditions were effective though less than the commonly used commercial diethyltoluamide