No abstract

This study investigated the suitability of small water bodies (SWBs) in the Lake Victoria basin, between November 2010 and October 2011 for increased food production through aquaculture. Sampling sites were stratified in terms of water availability and altitude. Low-altitude sites were represented by Yenga and Mauna dams in Siaya County, while high-altitude sites were represented by Kesses and Kerita dams in Uasin Gishu County. Variations in selected water quality parameters, nutrients, primary productivity (PP) and macroinvertebrate biomass of SWBs were investigated. The measured biological and water quality parameters measured in this study included PP of phytoplankton, macroinvertebrate biomass of the most abundant taxon, temperature, dissolved oxygen concentration, biochemical oxygen demand, pH, total nitrogen concentration and total phosphorus concentration. Descriptive statistics of mean and standard error of the mean were conducted for water quality parameters and nutrient levels. The general linear model was used to test for significant difference in nutrients and physicochemical parameters, both within and between the SWBs. ANOVA was used to test for any significant differences in both PP and biomass within and between the dams. PP and macroinvertebrate biomass were sufficiently high to support fish production, while all water quality parameters and nutrients were within acceptable ranges to support the life of the mostly cultured species. Based on the results of this study, the stocking of phytophagous and benthophagous fish is recommended as a means of exploiting the food resources and increasing fish production in these areas. 7.5 AE 0.23 23 AE 0.33 7.0 AE 0.50 3.4 AE 0.15 1.3 AE 0.06 0.20 AE 0.012 7.3 AE 0.09 22 AE 0.18 7.0 AE 0.45 3.0 AE 0.12 1.8 AE 0.05 0.12 AE 0.015 March 2011 7.6 AE 0.12 23 AE 0.42 7.4 AE 0.46 3.8 AE 0.25 1.4 AE 0.12 0.18 AE 0.009 7.5 AE 0.18 23 AE 0.80 7.2 AE 0.80 2.8 AE 0.20 1.6 AE 0.09 0.11 AE 0.001 April 2011 7.7 AE 0.40 21 AE 0.36 6.5 AE 0.42 3.9 AE 0.18 1.5 AE 0.05 0.15 AE 0.007 7.5 AE 0.15 21 AE 0.90 6.8 AE 0.25 3.0 AE 0.14 1.5 AE 0.10 0.09 AE 0.012 May 2011 7.4 AE 0.15 22 AE 0.45 7.5 AE 0.41 4.5 AE 0.12 1.6 AE 0.15 0.14 AE 0.006 7.4 AE 0.11 24 AE 0.85 6.7 7.4 AE 0.15 22 AE 0.33 7.8 AE 0.48 3.5 AE 0.10 1.6 AE 0.08 0.15 AE 0.015 7.4 AE 0.14 23 AE 0.45 7.0 AE 0.45 2.8 AE 0.20 1.7 AE 0.04 0.12 AE 0.003 August 2011 7.5 AE 0.30 23 AE 0.46 7.5 AE 0.49 4.1 AE 0.18 1.5 AE 0.12 0.16 AE 0.005 7.5 AE 0.08 25 AE 0.75 6.9 AE 0.75 3.1 AE 0.15 1.5 AE 0.01 0.06 AE 0.006 September 2011 7.6 AE 0.24 21 AE 0.50 7.4 AE 0.42 3.9 AE 0.22 1.6 AE 0.10 0.14 AE 0.008 7.7 AE 0.15 24 AE 0.50 6.5 AE 0.60 3.3 AE 0.12 1.8 AE 0.01 0.07 AE 0.015 October 2011 7.7 AE 0.25 22 AE 0.48 6.7 AE 0.42 3.8 AE 0.20 1.4 AE 0.05 0.14 AE 0.006 7.5 AE 0.12 22 AE 0.85 6.7 AE 0.20 3.2 AE 0.15 1.4 AE 0.02 0.08 AE 0.002 Yenga dam Mauna dam November 2010 7.4 AE 0.15 25 AE 0.55 7.0 AE 0.20 3.5 AE 0.20 0.9 AE 0.01 0.10 AE 0.001 7.6 AE 0.30 24 AE 0.55 5.6 AE 0.45 2.7 AE 0.20 1.1 AE 0.05 0.15 AE 0.004 December 2010 7.3 AE 0.20 26...

The study aimed at investigating the difference in relationship between the Length and Weight together with the Fulton's condition factor of O. niloticus within the open waters (wild) and cages of the winam gulf of L.Victoria, Kenya. This relationship and the condition factor 'K' were determined by taking the total length and weight of fish samples both from the cage and the open waters. The slope "b" of the regression analysis in both habitats revealed a positive allometric growth (3.16 and 3.09) for wild and cage respectively while the value of condition factor (K) for O. niloticus in wild and cage were found to be 1.44±0.1 and 1.38±0.15 respectively. Though O. niloticus performed well both in the wild and cage, there was a significant statistical difference in their health and general wellbeing. This was attributed to ecological differences between the two habitats. The assessment also showed that the culture of this Nile tilapia species in cages within winam gulf of L. Victoria can be economically sustainable if water quality parameters are properly monitored and point and non-point sources of pollution controlled.

This study was carried out in small water bodies (SWBs) within Uasin-Gishu and Siaya Counties of Kenya to investigate the effects of water quality on species diversity and richness of macroinvertebrates in these areas. The water quality of the SWBs was assessed in two dams in Uasin-Gishu County (Kesses and Kerita) and the other two in Siaya County (Mauna and Yenga) within Lake Victoria Basin. Water samples for total phosphorus (TP) and total nitrogen (TN) were collected at each sampling station and analyzed using standard methods and procedures. Physico-chemical parameters such as dissolved oxygen (DO), pH and temperature were taken in situ using electronic meters while biological oxygen demand (BOD) was analyzed using Winkler method after 5-days incubation period. Macroinvertebrate samples were collected using a scoop net (500 µm mesh size) then transferred into a white tray for washing and sorting prior to identification. Preliminary tests of water quality parameters were evaluated by GLM analysis of variance of which very significant differences were observed for both spatial (p = 0.004) and temporal (p= 0.001) variability with the measured water quality parameters. The results showed that there is both negative and positive change of macroinvertebrate composition and abundance between SWBs over time due to spatio-temporal variation of water quality parameters. Principle Component Analysis (PCA) further confirms this. PCA described over 90% of variation at the stations. For both seasons, TN, TP, temperature, pH, DO and BOD were found to have a significant influence of the species diversity, dominance and richness of macroinvertebrates. Principle component analysis of TN, TP, DO, pH and BOD for the SWBs described 96% of their variation when they were compared at temporal and spatial scales. This trend leads to the variation in species diversity; dominance and richness of macroinvertebrates in these SWBs. Water quality and littoral invertebrate mean relative abundance were significantly different among the studied small water bodies during the study period. Overall, water quality seemed to have had effect on species diversity, dominance and richness of the invertebrate benthic community therefore can be used as a bio-monitor to aquatic health.

Lake Victoria, Kenya has realized an increased number of fish cage culture for the last 10 years. The water quality monitoring study was undertaken at different private cage fish farm within the Winam gulf of L. Victoria, Kenya. In-situ measurements of key environmental parameters: temperature, dissolved oxygen, pH and total dissolved solids variables were taken each month for a period of 8 months. Environment parameters did not vary spatially or temporally between the cages and open waters of the gulf and were generally within safe ranges for freshwater habitats. This was attributed to the fact that the study areas were all within the same geographical space and lack of variation in micro-climatic conditions during the study period. The environmental variables were within the National Environmental and Management Authority (NEMA) and the desirable levels for cage culture. The study recommended that the efforts to promote commercial cage culture enterprises in Winam Gulf of L. Victoria and other water bodies should be enhanced on condition that the cages are sited in deep waters of the gulf with low cage concentration in a particular site and reduced stocking densities in order not to compromise the environmental quality, which can cause undesirable changes in natural biological productivity processes.