School of Natural Resources and Environmental Studies

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    REPRODUCTIVE PERFORMANCE OF NATURALIZED RAINBOW TROUT (Oncorhynchus mykiss, WALBAUM 1792) FROM SAGANA COLD WATER STREAM AND IMPLICATION ON FRY PRODUCTION FOR AQUACULTURE DEVELOPMENT IN KENYA
    (Karatina university, 2023-10) Njue, Justus Nyaga
    Naturalized rainbow trout (Oncorhynchus mykiss) populations form important recreational fishing resource in the world. Globally, rainbow trout is among the most widely introduced fish species and has been translocated outside its native home range, into at least 99 countries including the tropical regions where it has established naturalized populations. Information on the performance of the hatchery and wild populations of O. mykiss following spawning interactions has not been adequately explored especially in the tropical environments. The current study aimed at evaluating the spawning interactions between naturalized and wild O. mykiss from the high altitude second order stream, the Sagana in Kenya. Spawning and incubation were performed under controlled conditions in a hatchery facility to assess their performance. In each spawning process, total length, weight, condition factor and fecundity of the brooders were recorded. Fertilization rate, hatchability and survival of the fry were determined. Egg diameters were modelled as a function of biometric and reproduction parameters, using generalized linear model. Total fecundity of the broodstock differed significantly among the wild strain, hatchery reared and the cross between hatchery and wild stock (F = 8.934, df = 2, P = 0.0045). The fecundity of the broodstock varied with the average weight of the brooders where brooders with high average weight had a high fecundity. Relative fecundity was significantly different among the three groups of fish (F = 6.134, df = 2, P = 0.0217) but the differences between the hatchery and cross strain of wild and hatchery fish were not significant. Fertilization rate showed significant differences among fish in the three experimental groups (F = 10.136, df = 2, P = 0.0057), Eyed egg survival was lowest among the wild fish but showed no significant differences between the hatchery and cross between wild and hatchery strains. The study recommends the use of hatchery and wild crossed fish to support fry production for use in subsequent restocking of all trout streams in the country. Based on this study, management strategies involving restoration of trout population that would benefit anglers without reliance on importation of eyed eggs are recommended.
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    GROWTH PERFORMANCE OF RABBITFISH (Siganus sutor) REARED IN BRACKISH WATER EARTHEN PONDS, OFFERED BLACK SOLDIER FLY (BSF) LARVAE (Hermetia illucens)
    (Karatina University, 2022-11) OKEMWA, DOUGLAS MINYONGA
    The trend in mariculture development in Kenya is rising as the population and the demand for food increases. Rabbitfish (Siganus sutor) is a suitable candidate for mariculture in Kenya since it can be raised in ponds, accepts formulated feeds, and has a better growth performance as compared to other marine finfishes. It is also acceptable to local and international consumers and thus will have no marketing problem. Currently, S. sutor is the most targeted species and heavily fished on the Kenyan coast and Mariculture would increase its availability and sustainability. This study presents a 90 day’s first trial on the growth performance of S.sutor fed on black soldier fly meal in brackish water environment on the north coast in Kenya earthen ponds (hapa nets). The study had a complete block randomized design (CBRD) with four treatments, which were performed in triplicates and assigned randomly among twelve hapa net cages set in three rows (black nylon, sized (#1mm) and 1.5 x 1.0 x 1.2 meters). S.sutor were stocked at 15/fish/hapa and fed twice a day (0900HRS and 01600HRS) at 5% body weight throughout the study period. The cages were allocated treatments randomly as, T1 100% black soldier fly larvae, 0% fish meal, T2 25% fish meal replaced with 75% black soldier fly larvae), T3 50% fish meal was replaced with 50% BSFL and T4 was used as a control (40% commercial feed). Sampling was done monthly for total length (cm) and weight (g). The results showed that 100% BSFL feed had the highest initial mean weight of 36.06±0.99g, 40% commercial feed had the lowest at 33.76±0.68g. The highest final mean weight was observed in T1, (100% BSFL) at 68.36±0.42 and T2, (25% fish meal 75% BSFL) the lowest at 57.28±0.33g. Feed conversion ratio (FCR) in all diets and growth performance among the different treatments had no significant difference (p<0.05) at (F=6.9122, df=3, p<0.05). The water temperatures, pH, salinity, dissolved oxygen (DO), nitrogen (NH3-N), Nitrites - nitrogen (NO2-N) and total ammonia (NH3-N) values in all treatments were within the optimal limits for S. sutor growth. The study reports useful information on the growth performance and survival of S.sutor fed on black soldier fly larval diet. These findings, from this study revealed that S. sutor is suitable for culturing in brackish waters and the community can easily benefit from the species and act as food security and provide an alternative source of income for rural communities.
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    Impacts of Bush Encroachment By Euclea divinorum on Wildlife Species Diversity and Composition in Ol Pejeta Conservancy in Laikipia, Kenya
    (2018-09) Mutunga, Kavwele Cyrus
    Savannah landscapes are extensively social-economically important ecosystems which support livelihoods. Despite their importance, they are facing a biome shift due to natural and anthropogenic induced perturbations leading to increase in woody species, a phenomenon referred to as bush encroachment. In Ol Pejeta Conservancy (OPC), Euclea divinorum, unpalatable woody species has become a concern due to its invasion into other habitat types which can potentially affect resources for various feeding guilds, consequently affecting ecosystem services. This study examined vegetation cover changes from 1987 to 2016, topographic features attributable to these cover changes, differences in species diversity and composition in encroached and non-encroached habitats as well as habitat preference or avoidance by various feeding guilds in the conservancy. Landsat images acquired during dry seasons were processed and classified into various vegetation cover types. Infra-red motion triggered camera traps were deployed in 2km by 2km grids for 14 days and nights in June 2016 to examine species diversity, composition and habitat preference or avoidance by various feedings guilds in OPC. Results revealed that E. divinorum cover increased upward significantly from 1987-2016 (Mann Kendall test for trend analysis tau 1, n=6, p<0.01). Further, digital elevation models, contours and slope based normalized difference vegetation index had influence on encroachment patterns by E. divinorum. Shannon Weiner diversity revealed that species diversity and richness was higher in E. divinorum and lowest in Open grassland dominated areas while Hierarchical Cluster Analysis revealed that percentage similarity in species composition was highest between E. divinorum and mixed bushland habitats. Jacobs’ Index means revealed that E. divinorum habitat was significantly avoided by all feeding guilds (t1=2.253, d.f=3, p<0.01) while A. drepanolobium dominated habitats were significantly preferred (t1=2.353, d.f= 3, p=0.03). The findings show that increase in E. divinorum cover, which has higher species diversity and evenness, however is avoided by all feeding guilds in OPC. As such, there is need to actively manage encroaching species as well as further research on impacts of encroachment on grass biomass and diversity. These findings are beneficial to policy makers regarding management of healthy ecosystems.
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    Allometric Equations for Estimating Grevillea Robusta Biomass in Farming Landscapes of Maragua Sub-County
    (Karatina University, 2018-10) Owate, Augustine Omamo
    Grevillea robusta (Silk Oak) is widely interplanted with food crops in Maragua to enhance tree Biomass on farms. a practice that enhances biomass content on farms. However, models for estimating total biomass of G. robusta are lacking. This study sought to develop allometric equations for estimating G. robusta tree biomass using easily measurable predictor variables of bole diameter and height hypothesized as Biomass does not vary among tree components in different Agroecological Zones (AEZ), Tree component biomass does not differ with trees sizes G. robusta biomass stocks does not vary among AEZs. A stratified systematic sampling on Geographical Information System (GIS) platform was used to subdivide each of the four AEZs, Upper Midland 1 (UM1), Upper Midland 2 (UM2), Upper Midland 3 (UM3) and Upper Midland 4 (UM4) into three equal polygons. At the centre of each polygon, a one hectare sample plot was established and Diameter at Breast Height (DBH) for all G. robusta trees measured. Thirty three sample trees were randomly selected for destructive biomass measurements. They were felled, stumps uprooted and tree divided into different components. Samples for each component were weighed for fresh weights and oven dried at 1050C (woody components) and 700C (foliage). Biomass data for all sample trees was used to develop allometric equations. Fresh/dry weight ratios were computed and used to derive total biomass for each of the tree components and for the whole tree. The above ground and below ground biomass was used to calculate root/shoot biomass ratio (R/S) while root length and tree height were used to calculate root depth/tree height ratios. The linear, exponential, logarithmic, power and polynomial functions were used to estimate biomass from DBH and height data. The best fit equation was selected based on the lowest Standard Error of the Estimate (SEE), lowest Mean Residual Error (MRE) and Coefficient of determination (R2). Of the fitted functions the polynomial equations had the highest R2, lowest SEE and lower MRE values. The equation to estimate Total Tree Biomass (TTB) = 0.322DBH2+7.934DBH-19.26 (R2=0.99), Above Ground Biomass (AGB) = 0.248DBH2+6.243DBH-15.45 (R2=0.98) and Bellow Ground Biomass (BGB) = 0.074DBH2+1.688DBH-3.791 (R2 0.98). Use of height/or product of height and DBH as predictors resulted in a decrease in R2 and high SEE values. T-test for (AGB, BGB, TTB) indicated no difference between predicted and actual biomass (T=0.54,P=0.601,T=1.714,P= 0.117 and T = 0.422 ,P = 0.68 respectively). Developed equations were also compared with other existing equations for validation. The best fit equation estimated TTB in the AEZs was 13.926 tonha-1,13.109 tonha-1,10.869 tonha-1 and 11.827 tonha-1 in UM1, UM2, UM3 and UM4 respectively, showing uniformity of stocking across the landscape (F=2.87,P=0.675). DBH was found to be a reliable predictor of biomass (AGB, BGB and TTB) in farming landscapes of Maragua Biomass allocation to different tree components does not differ in the 4 AEZ implying that one allometric equation can be used to estimate the biomass of a specific tree component in all the AEZ of the study area but tree Biomass varies with tree sizes.. The developed equations will be useful in estimating G. robusta tree/component biomass in the farms in support of marketing for energy, timber and other wood uses in the area.
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    Department of Aquaculture and Fisheries Management
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    Department of Earth Science and Geo-Informatics
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    Department of Environmental Studies
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