This study, conducted in Nyanza Gulf of Lake Victoria, assessed ecological succession and dynamic status of water hyacinth. Results show that water hyacinth is the genesis of macrophyte succession. On establishment, water hyacinth mats are first invaded by native emergent macrophytes, Ipomoea aquatica Forsk., and Enydra fluctuans Lour., during early stages of succession. This is followed by hippo grass Vossia cuspidata (Roxb.) Griff. in mid- and late stages whose population peaks during climax stages of succession with concomitant decrease in water hyacinth biomass. Hippo grass depends on water hyacinth for buoyancy, anchorage, and nutrients. The study concludes that macrophyte succession alters aquatic biodiversity and that, since water hyacinth infestation and attendant succession are a symptom of broader watershed management and pollution problems, aquatic macrophyte control should include reduction of nutrient loads and implementing multifaceted approach that incorporates biological agents, mechanical/manual control with utilization of harvested weed for cottage industry by local communities.

This study was conducted from September to December 2008 to investigate the relative abundance of malaria vectors and schistosomiasis host snails associated with aquatic weeds in Nyanza Gulf (Lake Victoria). Larval and adult's stages of mosquitoes, lakeflies and snails were collected and identified with standard entomological and malacological techniques. The relative species composition and abundance of fish associated with macrophytes were also determined. Physicochemical parameters were determined with standard analytical methods. Community-based surveys were also conducted, using standard questionnaires, focused group discussions and direct observations. The results of this study indicated that the abundance of malaria-causing mosquitoes was low, accounting for only 0.4% of the total number of mosquitoes and lake flies collected from the gulf. Lake flies (Chaoborus and Chironomus spp.) were the most abundant flying insects associated with aquatic macrophytes (84.2%), followed by Culicines Culex spp. (12.2%) and Aedes spp. mosquitoes (3.2%). Biomphalaria sudanica and Bulinus africanus, the two most common hosts for schistosomiasis in the gulf, were detected in both types of macrophytes, but were most significantly attached to water hyacinth (P < 0.0001) and hippo grass (P = 0.0003). There were significantly fewer snails attached to the hippo grass, compared with those unattached in the open water (P < 0.05, GENMOD). Different habitats exhibited low Secchi disc transparency values, but elevated total phosphorous (TP), total nitrogen (TN), chlorophyll-a concentrations, as well as algal cell counts. Furthermore, Oreochromis niloticus and Haplochromine fishes were more abundant in water hyacinth mats compared with hippo grass mats and open-water habitats. The low mosquito abundance indicated that the sampled habitats were unsuitable for mosquito breeding, likely attributable to water turbulence and ⁄ or predation by larvivorous fish. The strong association between B. sudanica and B. africanus and aquatic macrophytes, and the observation that local communities perform many lakeshore-related activities that bring them into contact with water, can potentially lead to a higher prevalence of schistosomiasis in the Nyanza Gulf region.

Water samples for physico-chemical analysis for this study were collected monthly for five years between April 2008 and March 2013. Conductivity, temperature, dissolved oxygen and pH was measured in situ using a Surveyor II model hydrolab. Chlorophyll-a concentration was determined using a Genesys 10S Vis spectrophotomer. Nutrients were determined using standard methods and procedures. Analysis of Variance (ANOVA) was used to determine spatial and temporal variation in physicochemical and biological factors. Principal component analysis (PCA) was performed to establish the correlation of the physico-chemical and biological parameters among sampling stations and to group stations with similar physico-chemical parameters. Both spatial and temporal significant variations (P < 0.05) were detected in the concentrations of the nutrients measured during the study.

This study evaluated the effect of biofloc technology (BFT) on protein utilization and growth performance of Oreochromis niloticus fry under green house for 14 weeks under a 3 × 2 factorial design involving three crude protein (CP) levels (22, 27 and 35%) and two different carbon sources. Molasses and glucose were independently used as carbon sources in the BFT tanks with aeration using air stones. Mono-sex fish fry of mean weight 0.07 ± 0.01 g and total length 13.1 ± 0.01 mm were stocked at density of 1 fish per litre. The fishes were fed on the three commercial diets that were randomly assigned in triplicates, with the control treatment being 35% CP. Feeding was done twice daily at 5% body weight, while sludge was siphoned weekly. Calculations of specific growth rate (SGR), protein efficiency ratio (PER), food conversion ratio (FCR), survival and measurement of water quality parameters were also performed. Protein levels and carbon sources had significant effects (p < 0.05) on dissolved oxygen (DO) and NH 3 protein levels and carbon sources had significant interaction (p < 0.05) on pH.There was a significantly higher FCR in the control treatment (0.89) than in glucose (0.56-0.57) and molasses (0.59-0.63) bioflocs; furthermore, it was significantly different between the carbon sources. The PER was significantly higher in the control (8.42) than in glucose (5.03-7.99) and molasses (4.81-7.23) bioflocs. No significant interactions (p > 0.05) of protein levels and carbon sources were recorded on PER. However, it was significantly affected (p < 0.05) by protein levels and carbon sources. No significant effects (p > 0.05) of dietary protein level, carbon source, or their interaction were observed on SGR and condition factor. The SGR was significantly lower in the control (2.91) than glucose (3.52-3.59) and molasses (3.49-3.56) bioflocs. The condition factor was significantly lower in the control (0.81) than glucose (1.72-1.83) and molasses (1.82-1.84) bioflocs. Survival rates were significantly higher in glucose (>97%) and molasses (>94%) than the control with a lower value of 74.7%. The biofloc increased protein utilization efficiency, which improved FCR and enhanced fish growth rate evenThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

The present study demonstrates the application of a multi‐metric Phytoplankton Index of Biotic Integrity (PIBI) approach for ranking of major river catchments in the Kenyan part of Lake Victoria on the basis of their pollution status. The index utilizes water quality and zooplankton data, phytoplankton diversity, abundance and attributes, as well as literature information. The rivers were sampled from 2016 to 2018 during the wet season (March) and dry season (July). The separation power of the Mann–Whitney U test (p < .05) qualified eight discriminant metrics for phytoplankton samples into a scoring system of 1, 3 and 5, based on high, fair and slight deviation from the best site, respectively, in development of the final PIBI. The Kuja and Sondu‐Miriu rivers had the highest PIBI, signifying least pollution influence on the lake. In contrast, the Yala and Nzoia rivers exhibited the lowest PIBI, representing the catchments with a higher pollution influence on the lake. The fair to poor integrity classes for the major river catchments in the region signified a deteriorating lakescape. The present study presents the preliminary results of using phytoplankton metrics for development of the Index of Biotic Integrity (IBI) approach in the region as a decision‐making support tool for the effective management and sustainable use of water resources in the lake basin.

No abstract

The present study set out to investigate the haematological effects of tobacco leaf dust on African catfish, Clarias gariepinus, fingerlings, with a mean weight of 3.01 ± 1.25 g using “static renewal bioassay system” during a 120-hour bioassay exposure period. Water quality parameters such as pH and dissolved oxygen significantly decreased while total alkalinity and conductivity increased significantly in the exposed media, compared to the control test. Leucocytes counts increased significantly while erythrocytes counts decreased significantly with increasing concentration of tobacco dust. Packed cell volume significantly reduced with increase in the concentration of tobacco dust. Haematological examination showed that there was destruction of the erythrocytes production, and the concentration of haemoglobin was much lower in the exposed fish compared to the control depicting an anaemic condition. The results could provide baseline information for the safe limits of using tobacco leaf dust in fish ponds; hence 1.56 g L−1 concentration of tobacco leaf dust was recommended for pond preparation for Clarias gariepinus fingerling stocking. For better survival rates, the fish should only be introduced in the pond after three days of tobacco application.

In an attempt to describe the benthic macroinvertebrate assemblage of Lake Kenyatta and recommend possible interventions for sustainable management, sampling was done at different stations using an Eckman grab and a scoop net. At each station, six samples were taken (three grabs and three scoops). The samples were washed using a 300µm sieve, sorted live and identified to genus level and where possible to species level using appropriate keys. The specimens were further categorized into functional feeding guilds. The data were then analysed for diversity, evenness, abundance and dominance. Forty two species in 25 families and 13 orders were recorded. The organisms were further grouped into 4 functional feeding groups. The order Pulmonata dominated the macroinvertebrates sampled with 34.3% relative abundance while the lowest were Rhynchobdellida and Lepidoptera with 0.3% each. The high abundance of mollusks in the lake is probably an indication of absence of a predator. It is thus recommended that a fish species be introduced to convert these mollusks into fish biomass. This will enhance the economic gains and reduce the risk of bilhazia infestation since the host snail exists within the lake.