Spatial and seasonal variations of phytoplankton, expressed in terms of species composition, cell... more Spatial and seasonal variations of phytoplankton, expressed in terms of species composition, cell density, biovolumes and biomass, collected at 10 sampling sites in alkaline-saline Lake Nakuru, Kenya, were investigated monthly from March 2004 to February 2005, in relation to selected physical and chemical water quality parameters. A total of eight species, belonging to five genera and three classes, were recorded. The Cyanophyceae comprised the bulk of the phytoplankton, followed by Euglenophyceae, while Bacillariophyceae were the least abundant. Arthrospira fusiformis was the most dominant species, in terms of density, among the Cyanophyceae, while Euglena spp. and Navicula elkabs dominated the Euglenophyceae and Bacillariophyceae density, respectively. Seasonal variations in phytoplankton species composition, density and biomass were significant (P < 0.05) with minimum cell density and biomass occurring during the dry season, and being maximum following the end of the two rainy seasons from May to November 2004, suggesting the possible influence of various environmental factors on the lake. Sampling sites located close to the inlets of inflowing rivers exhibited significantly (P < 0.05) higher phytoplankton cell density and biomass than those by the inshore sites. Soluble reactive phosphorus, ammonia-nitrogen, conductivity and total alkalinity accounted for most of the variations in the cell densities of phytoplankton species.
Non-native freshwater fish species that have been introduced to the inland waters of Kenya are li... more Non-native freshwater fish species that have been introduced to the inland waters of Kenya are listed and the consequences of stocking such fish are reviewed. Original species composition and lake ecosystem function can be detrimentally affected but, also, the introduction of non-native species can result in significant economic benefit. In the context of impact on recipient fish communities and the performance of exploited fisheries, the merits or otherwise of alien fish species introductions are discussed with the aid of two case histories; lungfish (Protopterus aethiopicus) in Lake Baringo and a number of species, particularly carp (Cyprinus carpio), in Lake Naivasha.
Nile tilapia, Oreochromis niloticus together with other tilapiines of Oreochromis. leucosticus, T... more Nile tilapia, Oreochromis niloticus together with other tilapiines of Oreochromis. leucosticus, Tilapia. zillii and Sarotherodon melanopleudra (=T. rendalii) were introduced into Lake Victoria between 1951 and 1962 to boost the then declining fishery. Only O. niloticus was able to establish leading further to reduction in endemic tilapiines of Oreochromis variabilis and Oreochromis esculentus. O. niloticus currently forms the third commercially
Lake Naivasha is a freshwater lake situated in the eastern rift valley of Kenya. Only five specie... more Lake Naivasha is a freshwater lake situated in the eastern rift valley of Kenya. Only five species of fish are present, all of which have been introduced. They are Oreochromis leucostictus, Tilapia zillii, Micropterus salmoides (largemouth bass), Barbus amphigramma and Poecilia reticulata (guppy). The first three of these form the basis of an important gill net fishery and bass are also taken by rod and line for sport. Barbus are occasionally caught by dip net. Actual and potential yields for the Lake Naivasha fishery are discussed and the fishery is shown to be under-performing. The feeding regimes of the commercially exploited fish were examined in the context of available food supply, in particular the benthic fauna. Small bass depend heavily on Micronecta and large bass mostly take crayfish. Detritus predominates in the diet of Oreochromis leucostictus and Tilapia zillii but the former also eats algae and the latter, Micronecta and macrophyte. Various food resources, especially the benthos, appear to be under-utilized and so it is possible that further species could be introduced to enhance the commercial fishery.
Lakes and Reservoirs: Research and Management, 2005
Lake Victoria is Africa's most important source of inland fishery production, exhibiting annual c... more Lake Victoria is Africa's most important source of inland fishery production, exhibiting annual catches of ≈ 400 000 mt. The predatory Nile perch, Lates niloticus, and the herbivorous tilapiines, Oreochromis niloticus, Oreochromis leucostictus, Tilapia zillii and Tilapia rendalii, were introduced in Lake Victoria in the 1950s and 1960s. Nile perch were introduced to convert the abundant, but bony, haplochromines to fish flesh, while the tilapiines were introduced to boost the declining fishery. Since that time, the fisheries of Lake Victoria have undergone dramatic social and ecological changes. The catches increased tremendously, changing the fishery from artisanal to commercial, in turn increasing fisher income and employment opportunities. However, there was a decline and, in some cases, the disappearance of many indigenous fish species, especially the haplochromine cichlids. This reduction was attributed to overexploitation, predation, and competition and hybridization with the introduced species. The decline of the native fish species has had impacts on the trophic and ecological status of the lake. Nile perch now dominate the formerly complex food web. The loss of phytoplanktivorous haplochromines has contributed to an increase in algal blooms, reduction in water quality and occasional fish kills. Water hyacinth, Eichhornia crassipes, invaded Lake Victoria in 1988, with high rates of infestation in shallow waters and bays, which are breeding and nursery grounds for most fish species. Catches of Nile perch decreased following the infestation, while those of Nile tilapia, lung fish (Protopterus aethiopicus) and mud fish (Clarias gariepinus) increased. Haplochromines species also showed some signs of recovery. In view of all these changes, the future of the Lake Victoria fishery is uncertain.
Spatial and seasonal variations of phytoplankton, expressed in terms of species composition, cell... more Spatial and seasonal variations of phytoplankton, expressed in terms of species composition, cell density, biovolumes and biomass, collected at 10 sampling sites in alkaline-saline Lake Nakuru, Kenya, were investigated monthly from March 2004 to February 2005, in relation to selected physical and chemical water quality parameters. A total of eight species, belonging to five genera and three classes, were recorded. The Cyanophyceae comprised the bulk of the phytoplankton, followed by Euglenophyceae, while Bacillariophyceae were the least abundant. Arthrospira fusiformis was the most dominant species, in terms of density, among the Cyanophyceae, while Euglena spp. and Navicula elkabs dominated the Euglenophyceae and Bacillariophyceae density, respectively. Seasonal variations in phytoplankton species composition, density and biomass were significant (P < 0.05) with minimum cell density and biomass occurring during the dry season, and being maximum following the end of the two rainy seasons from May to November 2004, suggesting the possible influence of various environmental factors on the lake. Sampling sites located close to the inlets of inflowing rivers exhibited significantly (P < 0.05) higher phytoplankton cell density and biomass than those by the inshore sites. Soluble reactive phosphorus, ammonia-nitrogen, conductivity and total alkalinity accounted for most of the variations in the cell densities of phytoplankton species.
A study was conducted in the upper reaches of the River Njoro watershed to test the impacts of ch... more A study was conducted in the upper reaches of the River Njoro watershed to test the impacts of changing land-use patterns, from predominantly forest to pasture and agriculture, on benthic macroinvertebrate communities. Stream sampling sites were chosen to correspond to the main offstream land uses, including forests, grazing, small-scale agriculture, and intensive agriculture. Physicochemical variables were measured at each sampling site, and from collected water samples. Sampled macroinvertebrates were identified, and taxon diversity, richness, evenness and dominance were estimated for each site. Higher mean temperatures were recorded at the grazed and cultivated sites, compared to the forested sites. Higher ammonia concentrations were characteristic of the grazed parts of the watershed, while higher mean total phosphorus and total nitrogen concentrations were observed at the intensively cultivated sites. Baetis and Simulidae composed 65% by number of all the invertebrates collected. They dominated the benthos of the cultivated sections of the watershed, where they formed up to 75% of the observed invertebrate numbers. However, higher mean diversities, richness and evenness were recorded at forested sites, with a few taxa (notably Lepidostoma hirtum, Potamon sp., Leptophlebia sp. and Helodidae) being restricted to these unpolluted reaches, although many other taxa were common to all sites. Our findings suggest that a change from forestry to agriculture and grazing land uses have affected the physicochemical environment of the River Njoro, leading to a reduction in the diversity and evenness of benthic macroinvertebrates.
A comparison with previous studies in the gulf indicates that O. niloticus is now caught at a sma... more A comparison with previous studies in the gulf indicates that O. niloticus is now caught at a smaller mean size, whereas K, Z, and M have increased. Fish appeared to become sexually mature at a smaller size. Nile tilapia originally known to be herbivorous, feeding mostly on algae, has diversified its diet to include insects, fish, algae and plant materials, all being important food items. The changes in population characteristics and diet of O. niloticus are discussed in context of changes occurring in the lake and its surroundings.
Aquatic Conservation: Marine and Freshwater Ecosystems, 2009
1. The tilapia Oreochromis niloticus baringoensis is a genetically and morphologically distinct s... more 1. The tilapia Oreochromis niloticus baringoensis is a genetically and morphologically distinct sub-species of Oreochromis niloticus endemic to Lake Baringo, Kenya. In recent years, concern has been expressed as to its status. Recent declines in catch returns suggest the population may be threatened, with conservation action required to safeguard it. 2. Catch returns from the Baringo fishery since 1964 have shown considerable fluctuations for all species, but especially O. n. baringoensis. From a peak of 712 t in 1970, their total catch was only 5 t in 2005, despite a 2 year period of closure in 2002 and 2003. Changes in fishery catch and relative abundance were independent of exploitation in the fishery but were significantly correlated with lake level. 3. Few individuals were captured at lengths 4250 mm, with no fish sampled 4284 mm. During periods of high lake level, individuals matured at smaller sizes and were capable of growing to larger ultimate sizes. With maturity at lengths o130 mm and fishery regulations preventing removal of fish o180 mm, there was a relatively large proportion of mature fish that was below exploitation size each year (19 to 44%). In most years, the proportion of fish available for exploitation waso10%. 4. Stable isotope analyses revealed O. n. baringoensis was reliant upon planktonic basal resources and zooplankton carbon. There was only minimal trophic overlap with other fish species in the lake, indicating little potential for competition for food resources. 5. These data suggest that the population status of O. n. baringoensis is not threatened per se, but subject to an unpredictable and unstable environment that strongly influences their life-history traits and, ultimately, their population abundance, and should be managed accordingly.
... 3rd ed. WCB Publishers Everard M., Kuria A., Macharia M., Vale, JA, &amp; Harper, DM (200... more ... 3rd ed. WCB Publishers Everard M., Kuria A., Macharia M., Vale, JA, &amp; Harper, DM (2002) Aspects of the biodiversity of the rivers in the Lake Naivasha catchment. ... LakeNakuru integrated ecosystem management plan 2002-2012. ...
ABSTRACT Introduction Water resources within the River Njoro watershed have become degraded due t... more ABSTRACT Introduction Water resources within the River Njoro watershed have become degraded due to high population growth rate and change in land use upsetting environmental stability. Land cover classification using Landsat images (Baldyga et al., 2004) shows loss of about 20% of forested areas between 1986 and 2003 in the watershed. The forested and large-scale farm areas have been converted mainly into small-scale mixed agriculture and human settlements. These changes have impacted negatively on the ecological integrity and hydrologic processes in the watershed (Shivoga, 2001) but little is known about the influence of specific land uses on water quality of the river. Materials and methods Data recorded from ten sampling sites along River Njoro were used to examine the contribution of nutrients from subwatersheds upstream draining each of the sites. Standard Digital Elevation Model GIS analysis was used to determine the spatial distribution of land cover types and subwatershed contributing runoff to the sites in the river. Water and sediment samples were collected for chemical analysis related to upstream land use types and size of subwatersheds. Results The mid-stream portion of the river near Egerton University, with industrial, human settlement and agricultural land uses, accounted for the highest cover, the lower the P loss from the subwatershed There was, however, significant decrease in nutrient levels downstream indicating natural purification as the river flows through an area of large- scale farming with dense riparian vegetation. Small-scale farms and bare lands contribute over 55% of the phosphorus (P) load to the River Njoro. The size of the subwatershed accounts for about 53% variability in soluble P in the river. Grassland cover had a negative relationship with P loss (R2 = 0.4171) indicating that the more the grass cover, the lower the P loss from the subwatershed.
... M Marsabit Vincent I. Kinyua M Kiganjo Daniel Gisore M Bomet Timothy M. Ngumi M Kiambu Christ... more ... M Marsabit Vincent I. Kinyua M Kiganjo Daniel Gisore M Bomet Timothy M. Ngumi M Kiambu Christine Adhiambo F Uasu Gisu Roy Aseka M ... David K. Kemboi M Baringo John GE Bore M Mbeere Beatrice G. Akunga F Nairobi Peter N. Mwanzia M Nyambene Ceasar M. Kaiga M ...
A phenotypic marker in chromosome manipulation investigations is vital to interpreting induction ... more A phenotypic marker in chromosome manipulation investigations is vital to interpreting induction results. During earlier studies on androgenesis in tilapias, males of the homozygous recessive color mutation (blond) in Nile tilapia (Oreochromis niloticus; Egyptian strain, Lake Manzala) were used as an induction control to verify that progeny carried only the paternal genome. Control crosses between blond males and normal colored females (Ghana strain) produced viable progeny, but survival of androgenotes (paternal, blond) was extremely low. Severity of the induction treatment and inbreeding of the blond mutant were considered possible factors. An alternative approach is being tested which involves another color mutation as the phenotypic marker. Red tilapia also originated from the same population (Egyptian strain, Lake Manzala), but the color mutation is a dominant trait. Thus, red females and Ghana males are being used since the relatively unselected paternal genome of the Ghana strain might be hardier. However, the inheritance of the color and the pigment development pattern must be verified through progeny testing. The color pattern of red × red and red × Ghana is now being examined. Broodstock of these phenotypes and in these combinations have been pair spawned during the latter part of this reporting period.
Lakes Naivasha and Baringo in the eastern Rift Valley of Kenya are shallow, fresh-water lakes tha... more Lakes Naivasha and Baringo in the eastern Rift Valley of Kenya are shallow, fresh-water lakes that are subject to major fluctuations in water level and suffer from habi-tat degradation as a consequence of riparian activity. Lake Naivasha is approxi-mately 160 km2, is ...
Spatial and seasonal variations of phytoplankton, expressed in terms of species composition, cell... more Spatial and seasonal variations of phytoplankton, expressed in terms of species composition, cell density, biovolumes and biomass, collected at 10 sampling sites in alkaline-saline Lake Nakuru, Kenya, were investigated monthly from March 2004 to February 2005, in relation to selected physical and chemical water quality parameters. A total of eight species, belonging to five genera and three classes, were recorded. The Cyanophyceae comprised the bulk of the phytoplankton, followed by Euglenophyceae, while Bacillariophyceae were the least abundant. Arthrospira fusiformis was the most dominant species, in terms of density, among the Cyanophyceae, while Euglena spp. and Navicula elkabs dominated the Euglenophyceae and Bacillariophyceae density, respectively. Seasonal variations in phytoplankton species composition, density and biomass were significant (P < 0.05) with minimum cell density and biomass occurring during the dry season, and being maximum following the end of the two rainy seasons from May to November 2004, suggesting the possible influence of various environmental factors on the lake. Sampling sites located close to the inlets of inflowing rivers exhibited significantly (P < 0.05) higher phytoplankton cell density and biomass than those by the inshore sites. Soluble reactive phosphorus, ammonia-nitrogen, conductivity and total alkalinity accounted for most of the variations in the cell densities of phytoplankton species.
Non-native freshwater fish species that have been introduced to the inland waters of Kenya are li... more Non-native freshwater fish species that have been introduced to the inland waters of Kenya are listed and the consequences of stocking such fish are reviewed. Original species composition and lake ecosystem function can be detrimentally affected but, also, the introduction of non-native species can result in significant economic benefit. In the context of impact on recipient fish communities and the performance of exploited fisheries, the merits or otherwise of alien fish species introductions are discussed with the aid of two case histories; lungfish (Protopterus aethiopicus) in Lake Baringo and a number of species, particularly carp (Cyprinus carpio), in Lake Naivasha.
Nile tilapia, Oreochromis niloticus together with other tilapiines of Oreochromis. leucosticus, T... more Nile tilapia, Oreochromis niloticus together with other tilapiines of Oreochromis. leucosticus, Tilapia. zillii and Sarotherodon melanopleudra (=T. rendalii) were introduced into Lake Victoria between 1951 and 1962 to boost the then declining fishery. Only O. niloticus was able to establish leading further to reduction in endemic tilapiines of Oreochromis variabilis and Oreochromis esculentus. O. niloticus currently forms the third commercially
Lake Naivasha is a freshwater lake situated in the eastern rift valley of Kenya. Only five specie... more Lake Naivasha is a freshwater lake situated in the eastern rift valley of Kenya. Only five species of fish are present, all of which have been introduced. They are Oreochromis leucostictus, Tilapia zillii, Micropterus salmoides (largemouth bass), Barbus amphigramma and Poecilia reticulata (guppy). The first three of these form the basis of an important gill net fishery and bass are also taken by rod and line for sport. Barbus are occasionally caught by dip net. Actual and potential yields for the Lake Naivasha fishery are discussed and the fishery is shown to be under-performing. The feeding regimes of the commercially exploited fish were examined in the context of available food supply, in particular the benthic fauna. Small bass depend heavily on Micronecta and large bass mostly take crayfish. Detritus predominates in the diet of Oreochromis leucostictus and Tilapia zillii but the former also eats algae and the latter, Micronecta and macrophyte. Various food resources, especially the benthos, appear to be under-utilized and so it is possible that further species could be introduced to enhance the commercial fishery.
Lakes and Reservoirs: Research and Management, 2005
Lake Victoria is Africa's most important source of inland fishery production, exhibiting annual c... more Lake Victoria is Africa's most important source of inland fishery production, exhibiting annual catches of ≈ 400 000 mt. The predatory Nile perch, Lates niloticus, and the herbivorous tilapiines, Oreochromis niloticus, Oreochromis leucostictus, Tilapia zillii and Tilapia rendalii, were introduced in Lake Victoria in the 1950s and 1960s. Nile perch were introduced to convert the abundant, but bony, haplochromines to fish flesh, while the tilapiines were introduced to boost the declining fishery. Since that time, the fisheries of Lake Victoria have undergone dramatic social and ecological changes. The catches increased tremendously, changing the fishery from artisanal to commercial, in turn increasing fisher income and employment opportunities. However, there was a decline and, in some cases, the disappearance of many indigenous fish species, especially the haplochromine cichlids. This reduction was attributed to overexploitation, predation, and competition and hybridization with the introduced species. The decline of the native fish species has had impacts on the trophic and ecological status of the lake. Nile perch now dominate the formerly complex food web. The loss of phytoplanktivorous haplochromines has contributed to an increase in algal blooms, reduction in water quality and occasional fish kills. Water hyacinth, Eichhornia crassipes, invaded Lake Victoria in 1988, with high rates of infestation in shallow waters and bays, which are breeding and nursery grounds for most fish species. Catches of Nile perch decreased following the infestation, while those of Nile tilapia, lung fish (Protopterus aethiopicus) and mud fish (Clarias gariepinus) increased. Haplochromines species also showed some signs of recovery. In view of all these changes, the future of the Lake Victoria fishery is uncertain.
Spatial and seasonal variations of phytoplankton, expressed in terms of species composition, cell... more Spatial and seasonal variations of phytoplankton, expressed in terms of species composition, cell density, biovolumes and biomass, collected at 10 sampling sites in alkaline-saline Lake Nakuru, Kenya, were investigated monthly from March 2004 to February 2005, in relation to selected physical and chemical water quality parameters. A total of eight species, belonging to five genera and three classes, were recorded. The Cyanophyceae comprised the bulk of the phytoplankton, followed by Euglenophyceae, while Bacillariophyceae were the least abundant. Arthrospira fusiformis was the most dominant species, in terms of density, among the Cyanophyceae, while Euglena spp. and Navicula elkabs dominated the Euglenophyceae and Bacillariophyceae density, respectively. Seasonal variations in phytoplankton species composition, density and biomass were significant (P < 0.05) with minimum cell density and biomass occurring during the dry season, and being maximum following the end of the two rainy seasons from May to November 2004, suggesting the possible influence of various environmental factors on the lake. Sampling sites located close to the inlets of inflowing rivers exhibited significantly (P < 0.05) higher phytoplankton cell density and biomass than those by the inshore sites. Soluble reactive phosphorus, ammonia-nitrogen, conductivity and total alkalinity accounted for most of the variations in the cell densities of phytoplankton species.
A study was conducted in the upper reaches of the River Njoro watershed to test the impacts of ch... more A study was conducted in the upper reaches of the River Njoro watershed to test the impacts of changing land-use patterns, from predominantly forest to pasture and agriculture, on benthic macroinvertebrate communities. Stream sampling sites were chosen to correspond to the main offstream land uses, including forests, grazing, small-scale agriculture, and intensive agriculture. Physicochemical variables were measured at each sampling site, and from collected water samples. Sampled macroinvertebrates were identified, and taxon diversity, richness, evenness and dominance were estimated for each site. Higher mean temperatures were recorded at the grazed and cultivated sites, compared to the forested sites. Higher ammonia concentrations were characteristic of the grazed parts of the watershed, while higher mean total phosphorus and total nitrogen concentrations were observed at the intensively cultivated sites. Baetis and Simulidae composed 65% by number of all the invertebrates collected. They dominated the benthos of the cultivated sections of the watershed, where they formed up to 75% of the observed invertebrate numbers. However, higher mean diversities, richness and evenness were recorded at forested sites, with a few taxa (notably Lepidostoma hirtum, Potamon sp., Leptophlebia sp. and Helodidae) being restricted to these unpolluted reaches, although many other taxa were common to all sites. Our findings suggest that a change from forestry to agriculture and grazing land uses have affected the physicochemical environment of the River Njoro, leading to a reduction in the diversity and evenness of benthic macroinvertebrates.
A comparison with previous studies in the gulf indicates that O. niloticus is now caught at a sma... more A comparison with previous studies in the gulf indicates that O. niloticus is now caught at a smaller mean size, whereas K, Z, and M have increased. Fish appeared to become sexually mature at a smaller size. Nile tilapia originally known to be herbivorous, feeding mostly on algae, has diversified its diet to include insects, fish, algae and plant materials, all being important food items. The changes in population characteristics and diet of O. niloticus are discussed in context of changes occurring in the lake and its surroundings.
Aquatic Conservation: Marine and Freshwater Ecosystems, 2009
1. The tilapia Oreochromis niloticus baringoensis is a genetically and morphologically distinct s... more 1. The tilapia Oreochromis niloticus baringoensis is a genetically and morphologically distinct sub-species of Oreochromis niloticus endemic to Lake Baringo, Kenya. In recent years, concern has been expressed as to its status. Recent declines in catch returns suggest the population may be threatened, with conservation action required to safeguard it. 2. Catch returns from the Baringo fishery since 1964 have shown considerable fluctuations for all species, but especially O. n. baringoensis. From a peak of 712 t in 1970, their total catch was only 5 t in 2005, despite a 2 year period of closure in 2002 and 2003. Changes in fishery catch and relative abundance were independent of exploitation in the fishery but were significantly correlated with lake level. 3. Few individuals were captured at lengths 4250 mm, with no fish sampled 4284 mm. During periods of high lake level, individuals matured at smaller sizes and were capable of growing to larger ultimate sizes. With maturity at lengths o130 mm and fishery regulations preventing removal of fish o180 mm, there was a relatively large proportion of mature fish that was below exploitation size each year (19 to 44%). In most years, the proportion of fish available for exploitation waso10%. 4. Stable isotope analyses revealed O. n. baringoensis was reliant upon planktonic basal resources and zooplankton carbon. There was only minimal trophic overlap with other fish species in the lake, indicating little potential for competition for food resources. 5. These data suggest that the population status of O. n. baringoensis is not threatened per se, but subject to an unpredictable and unstable environment that strongly influences their life-history traits and, ultimately, their population abundance, and should be managed accordingly.
... 3rd ed. WCB Publishers Everard M., Kuria A., Macharia M., Vale, JA, &amp; Harper, DM (200... more ... 3rd ed. WCB Publishers Everard M., Kuria A., Macharia M., Vale, JA, &amp; Harper, DM (2002) Aspects of the biodiversity of the rivers in the Lake Naivasha catchment. ... LakeNakuru integrated ecosystem management plan 2002-2012. ...
ABSTRACT Introduction Water resources within the River Njoro watershed have become degraded due t... more ABSTRACT Introduction Water resources within the River Njoro watershed have become degraded due to high population growth rate and change in land use upsetting environmental stability. Land cover classification using Landsat images (Baldyga et al., 2004) shows loss of about 20% of forested areas between 1986 and 2003 in the watershed. The forested and large-scale farm areas have been converted mainly into small-scale mixed agriculture and human settlements. These changes have impacted negatively on the ecological integrity and hydrologic processes in the watershed (Shivoga, 2001) but little is known about the influence of specific land uses on water quality of the river. Materials and methods Data recorded from ten sampling sites along River Njoro were used to examine the contribution of nutrients from subwatersheds upstream draining each of the sites. Standard Digital Elevation Model GIS analysis was used to determine the spatial distribution of land cover types and subwatershed contributing runoff to the sites in the river. Water and sediment samples were collected for chemical analysis related to upstream land use types and size of subwatersheds. Results The mid-stream portion of the river near Egerton University, with industrial, human settlement and agricultural land uses, accounted for the highest cover, the lower the P loss from the subwatershed There was, however, significant decrease in nutrient levels downstream indicating natural purification as the river flows through an area of large- scale farming with dense riparian vegetation. Small-scale farms and bare lands contribute over 55% of the phosphorus (P) load to the River Njoro. The size of the subwatershed accounts for about 53% variability in soluble P in the river. Grassland cover had a negative relationship with P loss (R2 = 0.4171) indicating that the more the grass cover, the lower the P loss from the subwatershed.
... M Marsabit Vincent I. Kinyua M Kiganjo Daniel Gisore M Bomet Timothy M. Ngumi M Kiambu Christ... more ... M Marsabit Vincent I. Kinyua M Kiganjo Daniel Gisore M Bomet Timothy M. Ngumi M Kiambu Christine Adhiambo F Uasu Gisu Roy Aseka M ... David K. Kemboi M Baringo John GE Bore M Mbeere Beatrice G. Akunga F Nairobi Peter N. Mwanzia M Nyambene Ceasar M. Kaiga M ...
A phenotypic marker in chromosome manipulation investigations is vital to interpreting induction ... more A phenotypic marker in chromosome manipulation investigations is vital to interpreting induction results. During earlier studies on androgenesis in tilapias, males of the homozygous recessive color mutation (blond) in Nile tilapia (Oreochromis niloticus; Egyptian strain, Lake Manzala) were used as an induction control to verify that progeny carried only the paternal genome. Control crosses between blond males and normal colored females (Ghana strain) produced viable progeny, but survival of androgenotes (paternal, blond) was extremely low. Severity of the induction treatment and inbreeding of the blond mutant were considered possible factors. An alternative approach is being tested which involves another color mutation as the phenotypic marker. Red tilapia also originated from the same population (Egyptian strain, Lake Manzala), but the color mutation is a dominant trait. Thus, red females and Ghana males are being used since the relatively unselected paternal genome of the Ghana strain might be hardier. However, the inheritance of the color and the pigment development pattern must be verified through progeny testing. The color pattern of red × red and red × Ghana is now being examined. Broodstock of these phenotypes and in these combinations have been pair spawned during the latter part of this reporting period.
Lakes Naivasha and Baringo in the eastern Rift Valley of Kenya are shallow, fresh-water lakes tha... more Lakes Naivasha and Baringo in the eastern Rift Valley of Kenya are shallow, fresh-water lakes that are subject to major fluctuations in water level and suffer from habi-tat degradation as a consequence of riparian activity. Lake Naivasha is approxi-mately 160 km2, is ...
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