Papers by Julius O Manyala
Aquaculture
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Journal of Applied Ichthyology, Jun 1, 2008
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Journal of Great Lakes Research
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The dynamic behavior of a multi-species system that includes a prey refuge and a Holling type III... more The dynamic behavior of a multi-species system that includes a prey refuge and a Holling type III functional response is examined in this work. The pre-requisites for the presence of the equilibrium points, as well as their local and global stabilities, for the suggested system are analyzed and derived. The Routh-Hurwitz criterion and the eigenvalue technique are used to study the local stabilities. On the other hand, the global stabilities have been studied using the Lyapunov technique. Numerical simulations have been carried out using the Matlab ode45 solver software to verify the analytical results. The findings show that refuge plays a significant part in improving the dynamical stability of the system.
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Fundamental and Applied Agriculture
Globally, food insecurity is a fundamental problem. The aquaculture sector plays a vital role in ... more Globally, food insecurity is a fundamental problem. The aquaculture sector plays a vital role in supplying food with great potential to enhance food security. A significant challenge for the industry is the scarcity of protein sources in fish feeds and high prices that escalate production costs beyond economic viability. A growing paradigm shift for sustainability in the aquaculture sector is the usage of alternative insect-based diets like the black soldier fly (Hermetia illucens) larvae meal (BSFLM). The cost of fish production is always a pertinent issue in the aquaculture sector. Therefore, farmers would benefit from minimised and feed costs using technologies such as linear programming, which considers input costs and nutrient levels on different feed ingredients to ensure the production of least cost nutrient-dense diets. This study focused on applying the linear programming technique in Nile tilapia (Oreochromis niloticus) feed formulation using BSFLM as an alternative source...
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Fish require high quality protein in their rations which is sourced from fish meal. However, its ... more Fish require high quality protein in their rations which is sourced from fish meal. However, its scarcity and competition for use in livestock feeds has caused escalation of prices thus limiting its use. A study was carried out to evaluate protein quality of soybean-blood meal mixture as fish meal substitute in diets for Nile tilapia. Control diet, Fish meal based diet (R1) with 30% crude protein was formulated using fish meal, maize flour, wheat bran, sunflower oil and mineral-vitamin premix. Test diets (R2, R3, R4 and R5) were formulated replacing 25%, 50%, 75% and 100% of fish meal protein with soybean-blood meal mixture. Amino acids were determined using HPLC (AOAC, 2005) procedure. Fish meal had higher (p<0.05) levels of lysine (78.1 mg/g), arginine (58.7 mg/g) threonine (42.8 mg/g), Valine (54 mg/g) isoluecine (45.5 mg/g) phenylalanine and tyrosine (51.6 mg/g), methionine and cysteine (38.4 mg/g) and tryptophan (11.5 mg/g) than soybean-blood mixture. Soybeanblood meal was s...
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Aquaculture Research, 2020
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Lakes & Reservoirs: Science, Policy and Management for Sustainable Use
Lake Naivasha is a tropical freshwater body in Kenya, providing a source of livelihoods to the su... more Lake Naivasha is a tropical freshwater body in Kenya, providing a source of livelihoods to the surrounding communities. The lake ecosystem, however, has become degraded over time because of increasing pollutant loads from multiple sources, including human settlements and agricultural and surface runoff in its basin. Thus, it is vital to study the lake's water quality to determine its current status to inform appropriate management measures. Accordingly, the present study analysed water quality parameters and the trophic state of Lake Naivasha on the basis of water samples collected at eight sampling sites during the dry and wet seasons from December 2019 to May 2020. The physico‐chemical parameters were measured in situ, while nutrients were analysed in the laboratory. The results indicated high turbidity, total nitrogen (TN), ammonium‐nitrogen (NH4+‐N), nitrate‐N (NO3‐N) and total phosphorus (TP) levels during the wet season, and at the Malewa and Karati River mouths, while pH,...
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African Journal of Tropical Hydrobiology and Fisheries, 1998
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Recent fish introductions in Lake Victoria have had both positive and adverse implications on its... more Recent fish introductions in Lake Victoria have had both positive and adverse implications on its biodiversity and fisheries. This paper reviews the impact of six introductions in Lake Victoria basin with emphasis on areas where the introduced species have put more risks or benefits to the host environments. There have been six introductions of fish species (Lates niloticus, Oreochromis niloticus, Cyprinus carpio, O. melanopleura, O. leucostictus and Tilapia zillii) in Lake Victoria in a span of 20years. A significant ecological imbalance has been created through the depression of haplochromiine cichlids, changes in food webs and food chains, and alterations of water quality. There is evidence for example, that the introduced O. melanopleura has crossbred with T. zillii while O. niloticus has crossbred with O. variabilis with apparent dominance of the introduced species in these hybrids. The native species (Labeo victorianus, Barbus spp, Haplochromis spp., Protopterus aethiopicus, B...
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Aquaculture, Fish and Fisheries
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World Aquaculture, 2015
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Scientia Marina, 1995
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Africa Environmental Review Journal, Oct 13, 2021
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Papers by Julius O Manyala