Theses and Dissertations

ECOLOGICAL CARRYING CAPACITY AND GROWTH PERFORMANCE OF NILE TILAPIA (Oreochromis niloticus) IN CAGE AQUACULTURE WITHIN KADIMO BAY, LAKE VICTORIA, KENYA

Mon, 01 Jan 2024 00:00:00 GMT

ECOLOGICAL CARRYING CAPACITY AND GROWTH PERFORMANCE OF NILE TILAPIA (Oreochromis niloticus) IN CAGE AQUACULTURE WITHIN KADIMO BAY, LAKE VICTORIA, KENYA MAWUNDU, SELLU Fish production in the wild is decreasing globally due to a number of factors including overfishing, pollution, invasive species, and climate change effects. In Kenya, fisheries contribute less than 1% to the national GDP with an annual production of about 400, 000 mt against a demand of about 600,000 mt. Aquaculture production through innovative approaches such fish cage farming, has the potential to bridge the demand deficit. Despite the high potential for cage fish farming in Kenyan water bodies, there have been few studies focused on the effects of fish cages on water quality and trophic status, the nutrient carrying capacity of cage sites, and the appropriate stocking densities for cages in the water bodies. This study therefore was aimed to bridge these data gaps in order to facilitate sustainable management of the increasing fish cage farming of the Nile tilapia (Oreochromis niloticus) in Lake Victoria. Sampling for physico-chemical and biological variables, including nutrient load, was conducted from January to October 2021, at five fish cage sites and a control site within the Kadimo Bay,Lake Victoria, Kenya. The Carlson's Trophic State Index (CTSI) was used to classify the trophic state of the cage sites in the bay, and TN: TP ratio used to determine nutrient limitation in the bay. Fish cage optimum stocking density studies were carried in the bay from February to September 2022. Oreochromis niloticus fingerlings with initial mean (±SD) weight of 5.5 ± 1.72 g, were stocked at densities of 50, 75, 100, 125 and 150 fish m3 in replicate cages and growth and water quality changes monitored. The TP assimilation capacity and fish production potentials for the five cage sites within the bay were determined using a mass-balanced model. Results showed higher electrical conductivity (112.84 ± 1.94 μS cm-1 ) at cage sites compared to a Control site (97.53 ± 4.17 μS cm-1 ), similar variations were observed for nitrates and chlorophyll-a. However, 15 physico-chemical variables (DO, Temp., pH, TDS, Turb., TSS,POM, SRP, NO2 - , NO3 - , TN, TP, NH3, NH4 + , SiO4 4- ) did not vary significantly between the cage and control sites. The bay was evaluated as being in a light eutrophic state. Nitrogen as opposed to Phosphorus, was indicated to be the limiting nutrient for primary production in the bay. Growth performance results showed that fish stocked at lower densities (D50 & D75) had the highest growth performance in terms of mean weight gain (545.0 ± 15.81 and 527.4 ± 13.80 g, respectively). The Control treatment (D100), which is the normal stocking density used by cage fish farmers, showed intermediate mean weight gain (348.2 ± 11.48 g) which was significantly lower (p < 0.05) than for the D50 and D75 treatments. The feed conversion ratio (FCR) was lowest at D50 (1.2 ± 0.02) and highest at D150 (2.9 ± 2.01). Carrying capacity results, showed for all the five cage sites within the bay, the TP assimilation capacity was exceeded by the TP released by the fish cages. Additionally, the maximum estimated fish production capacities were much less than the current fish production levels for all the sites. Overall, although the results of this study showed cage aquaculture is not a current challenge to the water quality of the bay, regular monitoring is recommended to inform sustainable aquaculture development in the bay and the lake. It is recommended for fish farmers to stock fish at lower densities of 50 fish m 3 in order to maximize sustainable economic and environmental benefits of the cage culture system. Policies governing aquaculture production in the lake should be reviewed or enacted in order to include evidence-based information on environmental quality, sustainable production levels, and nutrient carrying capacity of the lake.

EVALUATION OF FARM-MADE AND COMMERCIAL FEEDS ON GROWTH AND ECONOMIC PERFORMANCE OF NILE TILAPIA (Oreochromis niloticus LINNAEUS, 1758) IN LIBERIA

Wed, 01 Jan 2014 00:00:00 GMT

EVALUATION OF FARM-MADE AND COMMERCIAL FEEDS ON GROWTH AND ECONOMIC PERFORMANCE OF NILE TILAPIA (Oreochromis niloticus LINNAEUS, 1758) IN LIBERIA HINNEH, MANDELA KLON-YAN A study on the effect of farm-made and commercial feeds on nutritional quality, growth, water quality and economic performance on Nile tilapia in landlocked Counties of in Liberia was done. Interviews and focus group discussions (FGDs) were used to collect information on farm made feeds. Moisture, crude protein, crude lipids and ash content of all feed ingredients were determined using AOAC procedures. Test diets consisted of two farmer diets, two commercial diets and one research diet. To determine the effect of these diets on fish growth, 450 male O. niloticus fingerlings of average weight of 13g were stocked in hapas mounted in 3 earthen ponds, each with 5 hapas at the Central Agriculture Research Institute in Liberia. The effect of diets on temperature, pH, and Dissolved Oxygen (DO) was determined using oxyguard and pH meters. Rate of returns on investment were used to evaluate the cost-effectiveness of all the diets. Of 120 farmers interviewed, 81.6% practice semi-extensive aquaculture in paddies, barrages, and earthen ponds. Farmers’ annual yield was 165.7 kg ha-1, translating to USD 414.25. The research diet had the greatest amount of crude protein (30.7%) while farmers’ diet had the lowest crude protein (9%). The research diet had the highest growth performance in terms of weight, attaining 175.33g. There was a significant difference in growth of fish between research and farmer (F1) diets (P = 2 × 10-5).There was no significant difference on the effects of each feed on the quality of the pond water Economic analysis indicated that the commercial diet (C1) was most profitable (USD 259.5). For better fish performance and profitability, there is need for researchers and feed producers to develop quality and affordable feeds for Liberia’s aquaculture sector while building capacity for farmers to formulate quality diets. Continuous monitoring of water quality is recommended for the sector.

Influence of net cages on water quality and trophic status of Lake Victoria, Kenya: The case of Kadimu Bay

Wed, 01 Mar 2023 00:00:00 GMT

Influence of net cages on water quality and trophic status of Lake Victoria, Kenya: The case of Kadimu Bay Mawundu, Sellu; et al. Water quality is a critical component regulating ecosystem functioning in aquatic habitats, requiring regular monitoring for sustainable ecosystem services. Cage fish farming has the potential to affect water quality because of its rapid increase in many African waterbodies in response to dwindling wild fish stocks. Thus, there is a need for more studies to guide sustainable cage aquaculture in African lakes and reservoirs. This study evaluated the possible effects of cage farming of Nile tilapia (Oreochromis niloticus) on water quality parameters and the trophic state of Kadimu Bay, Lake Victoria, Kenya. Sampling for physicochemical and biological variables, including nutrient load, was conducted from January to October 2021, at five fish cage sites and a control site within the bay. In situ measurements of physical variables were undertaken in the field, while analysis of water samples for nutrient loads, biological and chemical variables was undertaken in the laboratory, following the methods described in APHA (American public health association standard methods for the examination of water and waste water. APHA-AWWA- WEF, 2005). The Carlson's Trophic State Index (CTSI) was used to classify the trophic state of the cage sites, while the total nitrogen:total phosphorus (TN:TP) ratio was used to determine the primary productivity limiting nutrient in the bay. The study results indicated electrical conductivity was significantly lower at the control (97.53 ± 4.17 μS/cm), compared to cage sites (105.42 ± 5.32 μS/cm at the Utonga cage site to 112.84 ± 1.94 μS/cm at the Oele cage site), indicating water of relatively lower quality at the cage sites. Similarly, the nitrite concentrations were higher at cage sites (6.35 ± .96 μg/L at the Uwaria cage site to 3.16 ± 2.25 μg/L at the Utonga cage site), and lower at the control site (2.68 ± 1.39 μg/L). In all, 14 physicochemical variables did not vary significantly between the cage and control sites, with nine variables (temperature, turbidity, electrical conductivity, total suspended solids, particulate organic matter, chlorophyll-a, TP, nitrate and TN) being within the recommended thresholds for aquatic life processes. The bay was evaluated as being in a light eutrophic state, indicating moderate influence of the fish cages on the trophic state of the sites. There was a moderate relationship between chlorophyll-a and TP concentration at the sampling sites (R2 = .50), compared to a stronger relationship with NO− 3 (R2 = .78). The TN:TP ratios were <10 at the sampling sites, indicating nitrogen was the limiting factor for primary production in the bay. The calculated CTSI suggests that the bay exhibited a light eutrophic state. Overall, although the results of this study showed cage aquaculture is not a current challenge to the water quality of the bay, regular monitoring is nevertheless recommended to inform sustainable aquaculture development in the bay and lake.

ECOLOGICAL CARRYING CAPACITY AND GROWTH PERFORMANCE OF NILE TILAPIA (Oreochromis niloticus) IN CAGE AQUACULTURE WITHIN KADIMO BAY, LAKE VICTORIA, KENYA

Mon, 01 Jan 2024 00:00:00 GMT

ECOLOGICAL CARRYING CAPACITY AND GROWTH PERFORMANCE OF NILE TILAPIA (Oreochromis niloticus) IN CAGE AQUACULTURE WITHIN KADIMO BAY, LAKE VICTORIA, KENYA MAWUNDU, SELLU Fish production in the wild is decreasing globally due to a number of factors including overfishing, pollution, invasive species, and climate change effects. In Kenya, fisheries contribute less than 1% to the national GDP with an annual production of about 400, 000 mt against a demand of about 600,000 mt. Aquaculture production through innovative approaches such fish cage farming, has the potential to bridge the demand deficit. Despite the high potential for cage fish farming in Kenyan water bodies, there have been few studies focused on the effects of fish cages on water quality and trophic status, the nutrient carrying capacity of cage sites, and the appropriate stocking densities for cages in the water bodies. This study therefore was aimed to bridge these data gaps in order to facilitate sustainable management of the increasing fish cage farming of the Nile tilapia (Oreochromis niloticus) in Lake Victoria. Sampling for physico-chemical and biological variables, including nutrient load, was conducted from January to October 2021, at five fish cage sites and a control site within the Kadimo Bay,Lake Victoria, Kenya. The Carlson's Trophic State Index (CTSI) was used to classify the trophic state of the cage sites in the bay, and TN: TP ratio used to determine nutrient limitation in the bay. Fish cage optimum stocking density studies were carried in the bay from February to September 2022. Oreochromis niloticus fingerlings with initial mean (±SD) weight of 5.5 ± 1.72 g, were stocked at densities of 50, 75, 100, 125 and 150 fish m3 in replicate cages and growth and water quality changes monitored. The TP assimilation capacity and fish production potentials for the five cage sites within the bay were determined using a mass-balanced model. Results showed higher electrical conductivity (112.84 ± 1.94 μS cm-1) at cage sites compared to a Control site (97.53 ± 4.17 μS cm-1), similar variations were observed for nitrates and chlorophyll-a. However, 15 physico-chemical variables (DO, Temp., pH, TDS, Turb., TSS,POM, SRP, NO2-, NO3-, TN, TP, NH3, NH4+, SiO4 4-) did not vary significantly between the cage and control sites. The bay was evaluated as being in a light eutrophic state. Nitrogen as opposed to Phosphorus, was indicated to be the limiting nutrient for primary production in the bay. Growth performance results showed that fish stocked at lower densities (D50 & D75) had the highest growth performance in terms of mean weight gain (545.0 ± 15.81 and 527.4 ± 13.80 g, respectively). The Control treatment (D100), which is the normal stocking density used by cage fish farmers, showed intermediate mean weight gain (348.2 ± 11.48 g) which was significantly lower (p < 0.05) than for the D50 and D75 treatments. The feed conversion ratio (FCR) was lowest at D50 (1.2 ± 0.02) and highest at D150 (2.9 ± 2.01). Carrying capacity results, showed for all the five cage sites within the bay, the TP assimilation capacity was exceeded by the TP released by the fish cages. Additionally, the maximum estimated fish production capacities were much less than the current fish production levels for all the sites. Overall, although the results of this study showed cage aquaculture is not a current challenge to the water quality of the bay, regular monitoring is recommended to inform sustainable aquaculture development in the bay and the lake. It is recommended for fish farmers to stock fish at lower densities of 50 fish m3 in order to maximize sustainable economic and environmental benefits of the cage culture system. Policies governing aquaculture production in the lake should be reviewed or enacted in order to include evidence-based information on environmental quality, sustainable production levels, and nutrient carrying capacity of the lake.

INFLUENCE OF HIPPO AND CATTLE DUNG ON THE NUTRIENT LEVELS, ALGAL DIVERSITY, COMPOSITION, BIOMASS AND ECOSYSTEM METABOLISM IN AQUATIC ECOSYSTEMS: A MESOCOSM APPROACH

Sat, 01 Jul 2023 00:00:00 GMT

INFLUENCE OF HIPPO AND CATTLE DUNG ON THE NUTRIENT LEVELS, ALGAL DIVERSITY, COMPOSITION, BIOMASS AND ECOSYSTEM METABOLISM IN AQUATIC ECOSYSTEMS: A MESOCOSM APPROACH KIPLAGAT, MARY JEMAIYO Large mammalian herbivores (LMH) are major agents of the movement of terrestrial organic matter and nutrients into aquatic ecosystems, which can alter the structure and functioning of aquatic ecosystems. Populations of native large mammalian herbivores have been lost or displaced by livestock in many regions of the world, and this may result in changes in the functioning of the aquatic ecosystem due to significant differences in the quality of their dung. A replicated mesocosm experiment was conducted for six weeks (42 days) at the bank of Amalo river to study the influence of large mammalian herbivores (hippo and cattle) dung input on nutrient concentration, algal biomass, composition and diversity, and flume-scale ecosystem metabolism. The treatments included: H100 (no cattle dung, 100% hippo dung), H80 (20% cattle dung, 80% hippo dung), H60 (40% cattle dung, 60% hippo dung), H40 (60% cattle dung, 40% hippo dung), H20 (80% cattle dung, 20% hippo dung), and H0 (100% cattle dung, no hippo dung). These treatments were conducted in triplicate. Nutrients were analyzed by standard colourimetric methods, chlorophyll-a was extracted using methanol and measured spectrophotometrically, total suspended solids (TSS) and ash-free dry mass (AFDM) were determined gravimetrically and algae were counted under a microscope using the counter rafter cell and flume-scale ecosystem metabolism was measured in-situ using miniDOT loggers; where dissolved oxygen and the water temperature was recorded every one minute for the six weeks. Study results showed that cattle and hippo dung inputs have contrasting effects on aquatic ecosystem function; treatment with 100% cattle dung (H0) released higher amounts of limiting nutrients, exhibited higher algal biomass, higher algal abundance and diversity and supported higher rates of gross primary production (GPP) relative to 100% hippo dung (H100). Hippo dung, which has slower mineralization rates and larger particle sizes, increased water clarity relative to cattle dung. Differences in stoichiometry (C: N:P ratio) of major elements and faecal particle sizes between cattle and hippo dung were the likely drivers of decomposition and releasing rates of nutrients, which in turn influenced ecosystem processes differently. The study suggests that large mammalian herbivores (LMH) play a significant role in the movement of organic matter and nutrients from terrestrial to aquatic ecosystems. The loss or displacement of native LMH populations by livestock in various regions of the world can lead to changes in the functioning of aquatic ecosystems due to differences in the quality of their dung.

DYNAMICS IN TROPHIC STATUS, WATER AND NUTRIENT MASS BALANCE AND COMMUNITIES OF LAKE KANYABOLI, KENYA

Sat, 01 Oct 2022 00:00:00 GMT

DYNAMICS IN TROPHIC STATUS, WATER AND NUTRIENT MASS BALANCE AND COMMUNITIES OF LAKE KANYABOLI, KENYA KONDOWE, BENJAMIN NELSON Fishing pressure and nutrient enrichment from the catchment area threaten Lake Kanyaboli's water quality and communities. Understanding these impacts and their effect on the lake's water quality and communities is crucial for lake management and conservation. This study assessed the spatio-temporal variations in the physical, chemical, and biological variables, nutrient budget, plankton and fish communities of Lake Kanyaboli in western Kenya from February 2020 to February 2021. Primary and secondary data on water quality variables, including Secchi depth (SD), electrical conductivity (EC), temperature, pH, dissolved oxygen (DO) concentration, nitrates (NO3-), nitrite (NO2-), ammonium (NH4+), soluble reactive phosphorus (SRP), total phosphorus (TP) and total nitrogen (TN), and chlorophyll-a (Chl-a) were collected. Plankton and fish community data were also collected. Water quality variables and plankton communities were compared using two-way ANOVA, PCA, Pearson correlation, and descriptive statistics. The lake’s trophic status was calculated using SD, TP and Chl-a Carlson trophic status index (TSI) equations. Furthermore, PERMANOVA, Two-way nested ANOSIM, species diversity indices, CCA, NMDS, Kruskal Wallis test and SIMPER were also used to compare plankton and fish community data. Mass balance models were used to calculate water, nitrogen, and phosphorus mass balances. Two-way ANOVA on water quality variables showed no site × season interactions, while only Chl-a showed spatial variability. Significant seasonal differences were observed in SD, DO and Chl-a. Based on the Chl-a and SD TSI values, Lake Kanyaboli is eutrophic, whereas the TP value indicates hypereutrophic conditions. The nutrient mass balance showed that the lake receives more nutrient loads of N (90.78 t N year-1) and P (24.06 t N year-1) than it loses for both N (73.42 t N year-1) and P (15.76 t P year-1). Phytoplankton consisted of 30 genera dominated by Chlorophyceae (42.30%), with Bacillariophyceae, Cyanophyceae, Cryptophyceae, Euglenoidae, Trebouxiophyceae, and Zygnematophyceae also present. Fifteen zooplankton genera were also identified, including Cladocera (16.73%), Rotifera (27.86%) and Copepoda (55.41%). Although plankton abundance differed significantly between seasons, Two-way ANOVA showed no significant site × season interaction. The 2020 fish catch survey showed that Tilapia (50%), Clarias sp. (23%), Protopterus aethiopicus (20%), and haplochromines (7%) were the main fish species in the catch. But Kruskal Wallis showed no monthly variations in fish catches. The inter-annual fish catch and catch per unit effort (2003 to 2020) showed a decreasing trend. Despite infrequent historical data, physical, chemical, and biological variables captured anthropogenic effects over time, and the lake was eutrophic due to nutrient load. The phytoplankton community also showed that the lake was in a non-equilibrium state due to short water residence time and the uptake of nutrients by macrophytes bordering the lake. The major management issues identified are nutrient loading, fishing effort, and lake connectivity with the Yala River. Managing the catchment area holistically and monitoring the lake's water quality and fishing effort will help sustain goods and services, and livelihoods of Lake Kanyaboli riparian communities

NUTRITIONAL CONTENT OF FORMULATED FEEDS AND IN-SITU BASED FEEDS OF AQUACULTURE FISH IN THE WINAM GULF OF LAKE VICTORIA, KENYA

Sat, 01 Jan 2022 00:00:00 GMT

NUTRITIONAL CONTENT OF FORMULATED FEEDS AND IN-SITU BASED FEEDS OF AQUACULTURE FISH IN THE WINAM GULF OF LAKE VICTORIA, KENYA OTIENO, MELVINE ANYANGO The uses of feeds are critical to success of aquaculture farming on Lake Victoria Basin. The composition of the feeds can either be derived from in situ plants or animals i.e. the lake shrimp or omena within the ecosystem of Lake Victoria or externally sourced from outside the Lake i.e. imported formulated fish feeds. The net effect from the input of those feeds from outside could increase eutrophication within the lake while feeds derived from fauna and flora from the lake may not impact as negatively. The nutritional values of the feeds and the potentials of the feeds derived from outside the Lake and those utilizing local flora and fauna within the ecosystem of the lake are compared. The consequences of nutritional level from the different sources on the quality of fish product were estimated. Samples from both the formulated and in-situ based fish feeds were collected from aquaculture farms or from local sources around the Lake area. The samples were then freeze-dried and ground to fine local powder and dissolved using acid digest process. The resulting sample-acid solution was then analyzed using an Agilent 7500cx inductively -coupled plasma mass spectrometer (ICP-MS). With the exception of Arsenic (As), Barium (Ba) and Tin (Sn) wild fish muscle had significantly high PTEs in Silver (Ag), Chromium (Cr), Lithium (Li), Aluminium (Al), Cadmium (Cd), Mercury (Hg) and Lead (Pb) and also high in trace element concentrations in boron (B) and selenium (Se) compared to the caged fish muscle. Cadmium (Cd) and lead (Pb) contents in caged and wild fish samples were all below the FAO/WHO recommended limits. This study also showed that the differences were not quite discernable and that the data indicated are important preliminary findings that indicate that the differences in concentrations of micronutrients were wider than the differences in the concentrations of the macronutrients of the omena and lake shrimps of both closed and open lakes. The potentials of sustainable production of aquaculture especially caged culture from Lake Victoria is presented taking into account the optimal ratios measured in both formulated and in-situ based feed and their possible impact both economically and environmentally. Our study therefore; presents an environmentally sustainable means of solving food insecurity among the rapidly growing human population that suffers malnutrition, hunger, joblessness and disease

MODELLING LAKE LEVEL VARIATIONS, WATER BALANCE, AND FISHERIES OF LAKE BARINGO, KENYA

Sat, 01 Jan 2022 00:00:00 GMT

MODELLING LAKE LEVEL VARIATIONS, WATER BALANCE, AND FISHERIES OF LAKE BARINGO, KENYA RIZIKI, JACQUES WALUMONA Lake Baringo has the worst eroded catchment area and whose water levels (WLs) have been fluctuating at inter- and intra-annual time scales. These changes have been related to natural events and to human activities in the lake catchment. Changes in Lake Baringo water levels and water quality have affected fisheries production, ecological functioning and livelihoods. However, like for most tropical lakes, little is known about the linkages between WL changes, water quality parameters, fisheries production, and water/nutrient balance components of Lake Baringo. This study aimed to bridge this gap by modelling the linkages between WL variations, fisheries production, water quality, and water balance parameters of the lake. The study used both short and long-term datasets. Shortterm data were generated through monthly sampling of nine stations in the lake that extended from January 2020 to June 2021 while, long-term data (1956-2018) were sourced from grey and published data on the lake. Water samples were analyzed for selected physico-chemical variables using the standard methods for the analysis of water and wastewater at the Kenya Marine and Fisheries Research Institute (KMFRI) Baringo and Kisumu laboratories. Water balance of the lake was modeled through determination of input (river discharges, rainfall) and output (evaporation, abstraction, seepage) components of the balance. Lake level changes were analyzed based on annual and monthly deviations from long-term average (DLTM) and from patterns of lake level amplitude obtained from the annual/monthly maximum and minimum lake levels (WLamp). The fisheries and ecological functioning of Lake Baringo were described using the Ecopath mass-balanced model. Four main inputs required in the Ecopath model were used and included: biomass (B) production/biomass ratio (P/B), consumption/biomass ratio (Q/B), and ecotrophic efficiency (EE). Three annual Ecopath models (1999, 2010, 2020) were generated in order to compare the temporal trend in ecosystem functioning of the lake. Statistical approaches used to analyze the data majorly included; analysis of variance (ANOVA) applications, Locally-Weighted Scatter Plot Smoother (LOWESS), linear and waveform regression analyses, and Principal Component Analysis (PCA). Results indicated that, at inter-annual scale, the lake’s trophic status shifted from eutrophic to mesotrophic status at long-term (2008-2020) and short-term (2020-2021) scales, following the Carlson’s Trophic Status Index (CTSI) values. Water balance modelling indicated the water inputs from the runoff contributed for 75% in 1970-1995 and 71% in 2008-2021 to the lake’s storage while, direct precipitation into the lake contributed 25% in 1970-1995 and 29% in 2008-2021 to the lake’s storage, indicating that runoff is the major input component of Lake Baringo’s water balance. The water losses from the lake were contributed by evaporation (59-42%), abstraction (29-7%) and underground seepage (7-3%) during 1970-1995 and 2008-2021, respectively. Waveform regression significantly modeled DLTM and showed a 20-year oscillation between peak water levels in the lake. There were significant positive correlations between Water Level Fluctuations (WLFs) and both the water quality variables and Water Quality Index (WQI), and between fishery yields and WLFs in Lake Baringo. Three annual Ecopath models (1999, 2010, 2020) confirmed three trophic levels for the lake and suggested a strong bottom-up control in the lake’s food web. Oreochromis niloticus baringoensis is modeled as the keystone species in the lake. The Ecopath network analysis for the three models provided the ecosystem functioning and fisheries indicators whose temporal trends are variable and are described in the thesis. Overall, it is recommended that water resource management policies should guide the uses of water from the lake based on WHO guidelines. Water quality assessment, WLFs, species keystonness and other Ecopath results should be considered in the application of holistic and integrated lake basin management (ILBM) approaches in Lake Baringo and its watershed in order to sustain ecological services and the lake-dependent livelihoods.

EFFECT OF ELEVATED TEMPERATURE TREATMENT AND PAWPAW SEED POWDER ON PRODUCTION OF STERILE MONOSEX NILE TILAPIA

Tue, 01 Jan 2019 00:00:00 GMT

EFFECT OF ELEVATED TEMPERATURE TREATMENT AND PAWPAW SEED POWDER ON PRODUCTION OF STERILE MONOSEX NILE TILAPIA WAWERU, JERUSHA NJERI Nile tilapia is the most widely cultured fish species in Kenya. The greatest problem with tilapia is its prolific breeding due to mixed sex, resulting in stunted growth of the fish. Therefore, there was a need to employ simple techniques that embrace use of locally available materials for ease of implementation, which previous methods did not fully consider. This study therefore investigated the effect of high temperature treatment and pawpaw seeds powder on production of sterile monosex Nile tilapia (Oreochromis niloticus). The effect of high temperature treatment on sex differentiation and survival rate at different larval stages was studied; as well as the effect of pawpaw seeds powder on the histological structure of gonads, growth performance and proximate composition of O. niloticus. The research was carried out in two phases with 12 glass aquaria in each phase. In Phase 1 temperature treatment at 36 oC was done for 10 days at different days post-fertilization (dpf) of 1 dpf, 6 dpf and 10 dpf. The control was kept at 28 oC from the egg stage to the end of the experiment. In Phase 2 administration of pawpaw seeds powder to the fish from the best result of Phase 1 in terms of highest male ratio which was 10 dpf was done at 0g, 4g, 8g and 12g PSP/kg feed for a period of 60 days. Male percentage ranged from 45.56-82.22% while female percentage ranged between 17.78-54.44%. The control group had the least percentage of males (45.56%) while swim-up fry had the highest percentage of males (82.22%). Percent Survival was lowest at egg stage (43%) and highest at control group (80.7%). In Phase 2, histology of gonads of fish treated with different levels of PSP revealed that ovaries and testes of 0g PSP/kg feed were normal. Ovaries subjected to 4g PSP/kg feed had degenerative stromas while testes had scanty spermatozoa. At 8g PSP/kg feed, the ovaries showed increased atretic follicles and testes had degeneration of spermatozoa. Treatment with 12g PSP/kg feed resulted in severe atretic follicles of the ovaries and deformation of seminiferous tubules and erosion of spermatozoa of the testes. Proximate composition of the fish carcass showed that the 8g PSP/kg feed had the highest values (mean ± SE) of CP and ash (53.97 ± 0.094 and 20.05 ± 0.35) respectively. Body weight gain and Specific growth rate was highest at the 8g PSP/kg treatment level, but this treatment level had the lowest Feed Conversion Ratio. This study recommended the use of high temperature treatment of 36 oC to yield a high male percentage and this technique can be combined with the administration of pawpaw seeds powder to control the breeding of O. niloticus in production units.

DISTRIBUTION, ABUNDANCE AND SOME GROWTH ASPECTS OF SHARK SPECIES (PISCES: CHONDRICHTHYES) ON THE KENYAN COAST

Fri, 01 Jan 2016 00:00:00 GMT

DISTRIBUTION, ABUNDANCE AND SOME GROWTH ASPECTS OF SHARK SPECIES (PISCES: CHONDRICHTHYES) ON THE KENYAN COAST KIILU, BENEDICT KYALO In Kenya and most of the Western Indian Ocean (WIO) region, substantial amounts of shark landings occur as by-catch in artisanal fisheries, prawn trawls and longlines. However, the species structure, distribution, catch rates and levels of fisheries-shark interactions are not well studied. This information is, however, necessary to assess exploitation levels of shark species and for setting regulatory, conservation and management frameworks. This study therefore aimed at filling this information gap. Data were collected from fisher landings at various sites along the Kenya coast and by observers on commercial and scientific trawl surveys. Landings at six fish landing sites were inspected for sharks for 2-weeks in a month for 12 months (June 2012 to May 2013). Specimens were identified to species level and sex, length and weight recorded for each shark landed or trawled as by-catch. Results indicated that the catches are mainly dominated by hammerhead sharks (Sphyrna lewini, 53.7%), blacktip sharks (Carcharhinus limbatus, 33.7%), and grey reef sharks (Carcharhinus amblyrhynchos, 5.5%). Catch rates of species show spatial and seasonal variation, with higher catch rates in the middle coast (Malindi-Ungwana bay). Size-frequency distributions show mostly juveniles in the catches indicating fishers are probably exploiting nursery grounds. Fin weight was found to be 7.4% of body weight in S. lewini and 5.7% in C. limbatus. The sex ratios were significantly different in S. lewini (χ 2 = 36.62; df= 1; p= 0.00), C. limbatus (χ 2 = 7.03; df= 1; p= 0.008) and C. melanopterus (χ 2 = 34.77; df= 1; p= 0.00). In all three cases the female sex was dominant. The ratios for the other species assessed were close to unity. The study also provided length-weight and length-length relationships of the common shark species. Growth and mortality parameters are provided, for the first time, for the five common shark species in coastal Kenya. The results are discussed in relation to overfishing threats and behavioural ecology of the species. There is need to continuously monitor the distribution and abundance of sharks in Kenya and the WIO region for purposes of conservation, and an urgent need to set up a national plan of action to manage the shark stocks is recommended.