Research Repository :: Browsing by Author "Mgaya, Yunus D."

Browsing by Author "Mgaya, Yunus D."

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. Abundance and diversity of seagrass and macrofauna in the inter-tidal areas with and without seaweed farming activities in the east coast of Zanzibar
(2008) Lyimo, Thomas J.; Mvungi, Esther F.; Mgaya, Yunus D.
The diversity and abundance of seagrass and associated macrofauna were studied in transects with and without seaweed farms at Chwaka Bay and Jambiani, in the East Coast of Zanzibar. Eight seagrass species, namely Cymodocea rotundata, Cymodocea serrulata, Thalassia hemprichii, Thalassodendron ciliatum, Syringodium isoetifolium, Halodule uninervis, Halophila ovalis and Enhalus acoroides were recorded in the transects. The mean total biomass of seagrass at Chwaka Bay ranged from 142.4 ± 70.71 to 1652 ± 772.7 g dw/m2 and 212.9 ± 146.2 to 1829 ± 1692 g dw/m2 in station with and without seaweed farms, respectively. At Jambiani, the mean total biomass ranged from 880.4 ± 336.8 to 3467 ± 549.9 and 203.4 ± 102.4 to 3810 ± 2770 g dw/m2 in station with and without seaweed farms, respectively. The overall total biomass of seagrass was significantly lower (KW = 108.7, p < 0.0001) in station with seaweed farms than in stations without seaweed farms. A total of 93 macrofauna species representing 60 families were encountered and the mean density ranged from 910 to 6990 individuals/m2 at Chwaka Bay and Jambiani in stations with and without seaweed farms respectively. The most common macrofauna species were Codakia punctata, Meropesta nicobarica, Echinometra mathaei, Pinna muricata and Clibanarius emystemus. It was shown that the macrofauna abundance and diversity was higher in stations without seaweed farms than in the stations with seaweed farms, which could be due to activities associated with seaweed farming which contributed to the loss of diversity and biomass of flora and macrofauna of the seagrass meadows.
Abundance and Diversity of Seagrass and Macrofauna in the Intertidal Areas with and Without Seaweed Farming Activities in the East Coast of Zanzibar
(Tanzania Journal of Science, 2009-07) Lyimo, Thomas J.; Mvungi, Esther F.; Mgaya, Yunus D.
The diversity and abundance of seagrass and associated macrofauna were studied in transects with and without seaweed farms at Chwaka Bay and Jambiani, in the East Coast of Zanzibar. Eight seagrass species, namely Cymodocea rotundata, Cymodocea serrulata, Thalassia hemprichii,Thalassodendron ciliatum, Syringodium isoetifolium, Halodule uninervis, Halophila ovalis and Enhalus acoroides were recorded in the transects. The mean total biomass of seagrass at Chwaka Bay ranged from 142.4 ± 70.71 to 1652 ± 772.7 g dw/m2 and 212.9 ± 146.2 to 1829 ± 1692 gdw/m2 in station with and without seaweed farms, respectively. At Jambiani, the mean total biomass ranged from 880.4 ± 336.8 to 3467 ± 549.9 and 203.4 ± 102.4 to 3810 ± 2770 g dw/m2 in station with and without seaweed farms, respectively. The overall total biomass of seagrasswas significantly lower (KW = 108.7, p < 0.0001) in station with seaweed farms than in stations without seaweed farms. A total of 93 macrofauna species representing 60 families were encountered and the mean density ranged from 910 to 6990 individuals/m2 at Chwaka Bay andJambiani in stations with and without seaweed farms respectively. The most common macrofauna species were Codakia punctata, Meropesta nicobarica, Echinometra mathaei, Pinna muricata and Clibanarius emystemus. It was shown that the macrofauna abundance and diversity was higher in stations without seaweed farms than in the stations with seaweed farms, which could be due to activities associated with seaweed farming which contributed to the loss of diversity and biomass of flora and macrofauna of the seagrass meadows.
Biological connectivity and nursery function of shallow-water habitats in Chwaka Bay
(2012) Gullström, Martin; Dorenbosch, Martijn; Lugendo, Blandina; Mwandya, Augustine W.; Mgaya, Yunus D.; Berkström, Charlotte
Changes in species composition and abundance of commercially important fish population in Kigoma Area, Lake Tanganyika, Tanzania
(2008) kimirei, Ismael; Mgaya, Yunus D.; Chande, A. I.
The pelagic fishery of Lake Tanganyika provides employment to about 1 million consumers and protein to many more people living around the lake. It is mainly based on three commercially important fish species namely two clupeids Stolothrissa tanganicae and Limnothrissa miodon commonly known as “dagaa” and a perch Lates stappersii. A declining trend of the perch both in its composition and abundance in the pelagic fish landings is partly tied to local over-fishing and climate change. There are three important periods in the exploitation process identified as: (1) a traditional fishery period, the pre-1975 period marked by low catches of Lates spp. and a dominance of clupeids; (2) an industrial fishery period (1975–1978) marked by high catches of Lates stappersii and high total landings; and (3) an artisanal fishery period (post 1984) with relatively low catches and high dominance of clupeids especially Stolothrissa tanganicae. Population growth and refugee influx from the politically volatile Burundi and Democratic Republic of Congo both caused high fish protein demand, particularly for dried clupeids. Also changes in the rural economy caused by drought in the area are resulting into high exploitation pressure on the pelagic resources. Concerted efforts to prevent/reduce exploitation pressure on the pelagic fish resources should take into action a lake wide management strategy where by management issues in all the riparian countries should be harmonized. More effort should be geared towards preventing the use of beach seines and small meshed nets subsequently ensuring a sustainable utilization of the pelagic fish resources.
Coastal and Marine Fisheries: Towards a New Vision for the Exploitation and Sustainable Management of Africa’s Fishery Resources
(2005) Ba, Moctar; Berraho, Abdellatif; Biodiguel, Clotide; Cunningham, stephen; Mgaya, Yunus D.
Coastal resources and their use. In: Eastern Africa Atlas of Coastal Resources
(UNEP, 2001-01) Francis, Julius; Mahongo, Shigalla B.; Semesi, A.; Muhando, Christopher A; Mgaya, Yunus D.; Daffa, J.; Ngoile, Magnus
Coastal resources utilization and conservation issues in Bagamoyo, Tanzania
(1998) Semesi, A. K.; Mgaya, Yunus D.; Muruke, M. H. S.; Francis, Julius; Mtolera, Matern; Msumi, G.
A study was carried out to provide information about the importance of the management of coastal resources in Bagamoyo, Tanzania. The results showed that the coral reefs at Mwamba Kuni and Mshingwi are the main fishing grounds for the artisanal fishermen. Trawlers compete and conflict with artisanal fishermen. The mangroves provide habitats for fish and other animals and are a source of fuelwood, charcoal, fishing stakes, building materials, and traditional medicines. Solar salt production is also an important activity. Although Bagamoyo depends on renewable resources, the harvesting rates of most resources are not known. Habitat destruction and overexploitation of resources have resulted in declining catches. There is unawareness among the resource users of the linkages between the various coastal ecosystems, but they do have vast traditional knowledge about the resources. In this article, we present the crustacean resources, fish, sea cucumbers, mangrove products, coral reefs, tourism, and salt production activities.
A comparison of diurnal dynamics of water quality parameters in Nile tilapia (Oreochromis niloticus, Linnaeus, 1758) monoculture and polyculture with African sharp tooth catfish (Clarias gariepinus, Burchell, 1822) in earthen ponds.
(Springer, 2014) Shoko, Amon P.; Samwel Mchele Limbu; Mrosso, Hillary D. J.; Mgaya, Yunus D.
The overall performance of an aquaculture system is partly determined by its water quality parameters. Poor water quality stresses and adversely affects fish growth causing low production, profit and product quality. Diurnal dynamics of water quality parameters were investigated in Nile tilapia (Oreochromis niloticus) monoculture and polyculture with Clarias gariepinus in earthen ponds. Dissolved oxygen, temperature and pH were measured and monitored for 24 h. Water samples for nutrient analysis were collected from the middle of ponds in triplicate at about 30–35 cm below the water surface using a plastic bottle. Nitrite–nitrogen (NO2–N), nitrate–nitrogen (NO3–N), unionised ammonia (NH3–N), soluble reactive phosphorus and free carbon dioxide were analysed following standard methods and procedures. The results show that dissolved oxygen concentrations during the past midnight and pre-dawn hours were significantly lower than the levels in the morning and afternoon hours (ANOVA, F = 45.709, P < 0.05) which is dangerous to the life of the cultured fishes. The levels of unionised ammonia and temperature were higher and lower, respectively, than the acceptable levels for optimum growth of O. niloticus and C. gariepinus. Nitrite–nitrogen, nitrate–nitrogen, pH, soluble reactive phosphorus and free carbon dioxide were within the recommended limits for fish growth in aquaculture. Growth parameters, feed conversion ratio and survival rate were not significantly different between culture systems (P > 0.05). Fish yield was relatively higher in polyculture (45.74 ± 0.44 tons/ha) than monoculture (30.77 ± 0.54 tons/ha). During fish farming, optimum fish growth and hence economic benefits can be accrued by devoting some efforts on monitoring the fish pond water at regular intervals. This quality assurance process will ensure that fish farmers produce fish with maximum growth and yield without polluting pond water and the surrounding environment.
Coral bleaching and habitat effects on colonisation of reef fish assemblages: An experimental study
(Elsevier, 2011) Yahya, Saleh A.S.; Gullström, Martin; Öhman, Marcus C.; Jiddawi, Narriman S.; Andersson, Mathias H.; Mgaya, Yunus D.; Lindahl, Ulf
Degradation and mortality of corals is increasing worldwide and is expected to have significant effects on coral reef fish; hence studies on these effects are essential. In the present study, a field experiment was set up within Mafia Island Marine Park in Tanzania (East Africa) to examine the effects of bleaching and habitat structure on colonisation of coral reef fish assemblages. Live and bleached staghorn coral Acropora formosa was transplanted onto plots in a site dominated by sand and rubble, and the experimental design comprised of three treatments: live coral, bleached coral and eroded coral rubble. There was an immediate increase (within 24 h) in fish abundance and diversity in the two treatments with standing corals. Overall, live and bleached coral plots showed similar effects, but differed from the eroded coral plots which had a much lower abundance and diversity of fish. In general, fish species diversity changed with time over the study period while fish abundance did not. Multivariate analyses showed that while there were differences in fish assemblage structure between standing corals and the eroded coral treatment, there was neither a difference between live and bleached coral treatments nor any temporal effects on fish assemblage structure. Our findings suggest that physical structure and complexity of habitat have stronger effects on colonisation of reef fish assemblages than changes in coral health (such as bleaching) which do not affect coral structure. This may have important implications for appropriate coral reef management.
Coral bleaching and habitat effects on colonization of reef fish assemblages: an experimental study.
(Coral bleaching and habitat effects on colonization of reef fish assemblages: an experimental study., 2011) Ulf, Lindahl; Mgaya, Yunus D.; Mathias H., Andersson; Narriman S., Jiddawi; Marcus C., Ohman; Martin, Gullstrom; Saleh A. S., Yahya
Degradation and mortality of corals is increasing worldwide and is expected to have significant effects on coral reef fish; hence studies on these effects are essential. In the present study, a field experiment was set up within Mafia Island Marine Park in Tanzania (East Africa) to examine the effects of bleaching and habitat structure on colonisation of coral reef fish assemblages. Live and bleached staghorn coral Acropora formosa was transplanted onto plots in a site dominated by sand and rubble, and the experimental design comprised of three treatments: live coral, bleached coral and eroded coral rubble. There was an immediate increase (within 24 h) in fish abundance and diversity in the two treatments with standing corals. Overall, live and bleached coral plots showed similar effects, but differed from the eroded coral plots which had a much lower abundance and diversity of fish. In general, fish species diversity changed with time over the study period while fish abundance did not. Multivariate analyses showed that while there were differences in fish assemblage structure between standing corals and the eroded coral treatment, there was neither a difference between live and bleached coral treatments nor any temporal effects on fish assemblage structure. Our findings suggest that physical structure and complexity of habitat have stronger effects on colonisation of reef fish assemblages than changes in coral health (such as bleaching) which do not affect coral structure. This may have important implications for appropriate coral reef management.
Cyanobacteria blooms—A possible cause of mass mortality of Lesser Flamingos in Lake Manyara and Lake Big Momela, Tanzania
(Elsevier, 2006) Lugomela, Charles; Pratap, Harish B.; Mgaya, Yunus D.
Limnological studies were conducted in three alkaline lakes (Lake Big Momela, Manyara and Embagai) with the aim of investigating the cause of mass mortality of the Lesser Flamingos in Lake Manyara and Lake Big Momela during July–August 2004. High concentrations, up to 150 million filaments per liter of the potentially toxic planktonic cyanobacterium Arthrospira fusiformis were found in surface scum of Lake Big Momela where Lesser Flamingos were dying at a rate of between 15 and 50 individuals per day during the study period. Gut content analyses indicated that A. fusiformis was the main food item in moribund flamingos. Mouse bioassay suggested that the crude microalgal extract dominated by A. fusiformis was toxic with all mice close to death becoming lethargic, with loss of balance, uncoordinated movements, intermittent tremors, dyspnoea with gasping followed by respiratory arrest. This observation gives circumstantial evidence that A. fusiformis at such high concentrations was toxic to the Lesser Flamingo in Lake Big Momela. # 2005 Elsevier B.V. All rights reserved.
Cyanobacteria blooms–a possible cause of mass mortality of Lesser Flamingos in Lake Manyara and Lake Big Momela, Tanzania
(Elsevier, 2006) Lugomelaa, Charles; Pratapb, Harish B.; Mgaya, Yunus D.
ical studies were conducted in three alkaline lakes (Lake Big Momela, Manyara and Embagai) with the aim of investigating the cause of mass mortality of the Lesser Flamingos in Lake Manyara and Lake Big Momela during July–August 2004. High concentrations, up to 150 million filaments per liter of the potentially toxic planktonic cyanobacterium Arthrospira fusiformis were found in surface scum of Lake Big Momela where Lesser Flamingos were dying at a rate of between 15 and 50 individuals per day during the study period. Gut content analyses indicated that A. fusiformis was the main food item in moribund flamingos. Mouse bioassay suggested that the crude microalgal extract dominated by A. fusiformis was toxic with all mice close to death becoming lethargic, with loss of balance, uncoordinated movements, intermittent tremors, dyspnoea with gasping followed by respiratory arrest. This observation gives circumstantial evidence that A. fusiformis at such high concentrations was toxic to the Lesser Flamingo in Lake Big Momela.
Demography of fish populations reveals new challenges in appraising juvenile habitat values.
(2013) Kimirei, Ismael; Nagelkerken, Ivan; Slooter, N.; Gonzalez, E. T.; Huijbers, Chantal; Mgaya, Yunus D.; Rypel, Andrew
Understanding the ‘value’ of nursery habitats is increasingly perceived as essential to conservation management of marine ecosystems globally. Yet, most work on this topic has assumed that population dynamics are temporally and spatially static, which clearly oversimplifies some highly complex and integral ecological processes. We used size-frequency data of fish species from mangrove and seagrass habitats collected at various locations over a >2 yr period to explore demographic structure and variability along with potential factors (such as growth, food abundance, and relative predation risk) that might encourage such variability. While demographics were skewed predominantly towards juveniles, older fish (up to 13 yr) were regularly observed in some mangroves or seagrass beds, indicating relatively complex population demographics. Juvenile habitats varied substantially in both prey abundance and relative predation risk—an effect that appeared to give rise to habitat-specific differences in somatic growth rates and fish densities. Fish population size structure was further related to position within the seascape, suggesting complex spatial dynamics in the production of fish biomass. Our results demonstrate that effectively appraising juvenile habitats will be a more convoluted process than previously thought, as greater integration is needed between basic ecological processes (e.g. predation risk and food availability) and population demography. Whereas current approaches often identify and manage single, complete nursery habitats based on those that contribute most individuals to adult populations, our study shows that a more dynamic and spatially-explicit management approach is needed, as nurseries have divergent benefits for separate life stages, species, and locations.
Diel vertical distribution and life history characteristics of Tropodiaptomus simplex and its importance in the diet of Stolothrissa tanganicae, Kigoma, Tanzania.
(2014) Mgana, H. F.; Herzig, Alois; Mgaya, Yunus D.
Tropocyclops simplex abundance, diel distribution and the impact of the planktivore fish Stolothrissa tanganicae on the T. simplex population were studied at a deep-water site in Kigoma Bay, Lake Tanganyika during the wet period (October 2008–February 2009). The top 40 m were examined using discrete depth samples, filtered through a 40-μm mesh. Ovigerous and copepodids of Tropodiaptomus simplex exhibited a very clear diel vertical migration. Ovigerous females of Tropodiaptomus were negligibly low in the 0–30 m depth during the day, while at night they stayed above 20 m. Tropodiaptomus nauplii did not show any clear diel vertical migration. The contribution of adults, copepodite and nauplii stages to the total numbers of Tropodiaptomus simplex was 8.2, 8.6 and 83.2%, respectively. Stolothrissa tanganicae stomachs were analysed to quantify the contribution of zooplankton in their diets, which revealed a dominance of Tropodiaptomus females and the electivity indices proved that T. simplex females (with or without eggs) were highly selected by S. tanganicae, which could probably be explained by size-selective feeding. Life table analysis indicated that approximately 60% of T. simplex nauplii did not develop into copepodites, a loss which could not be explained by the results of the present study. 68% of the fish gut contents were contributed by female Tropodiaptomus individuals and the contribution of shrimps and Cyclopidae increased substantially to almost 20%. S. tanganicae consumed largely ovigerous Tropodiaptomus females. However, eggs found in the guts were significantly smaller than those found in the zooplankton discrete samples, suggesting that digestion had started. The calculated electivity indices underline that ovigerous and non ovigerous females of T. simplex are being positively selected in the feeding process. It infers existence of selective predation in L. Tanganyika by S. tanganicae on females of T. simplex (with or without eggs) and as a result distinct vertical migration as a predation escape mechanism is performed.
Distribution patterns of the striped mullet (Mugil cephalus) in mangrove creeks of Zanzibar, Tanzania. African Journal of Marine Science
(2010) Gullström, Martin; I, Bryceson; Öhman, Marcus C; Mgaya, Yunus D.; Mwandya, Augustine W.
Spatial and seasonal variations in density of striped mullet Mugil cephalus were investigated in four mangrove creeks in Zanzibar, Tanzania, during a one-year cycle. Fish were collected monthly in the lower, intermediate and upper reaches of each creek using a beach-seine net. All fish collected were juveniles between 2 and 16 cm standard length. The density of juvenile mullet differed significantly among the creeks, but the spatial patterns within them were consistent with higher densities upstream in three of the creeks. Generally, small mullet (2–10 cm) were more abundant in the upper reaches compared to the lower and intermediate reaches. Seasonal patterns were weak, although mullet densities were high during the period of heavy rains (March–May). Principal component analysis showed that a muddy substrate with microphytobenthos was positively correlated with high mullet densities, although site-specific variables such as shallow water depth and water clarity were also significantly correlated. Our findings suggest that the densities of juvenile striped mullet vary among sites and creeks in response to refuge availability from turbid, shallow water and the accessibility of food from benthic microalgae.
Eastern Africa Atlas of Coastal Resources: Tanzania
(2001) Francis, Julius; Mahongo, Shigalla B.; Semesi, A. K.; Muhando, Christopher A.; Mgaya, Yunus D.; Daffa, J.; Ngoile, Magnus
Ecosystem engineering potential of the gastropod Terebralia palustris (Linnaeus, 1767) in mangrove wastewater wetlands - A controlled mesocosm experiment
(2010) Kristensen, Erik; Mgaya, Yunus D.; Cannicci, Stefano; Samwel Mchele Limbu; Bartolini, Fabrizio; Penha-Lopes, Gil Pessanha
The effect of different sewage concentrations (0, 20, 60 and 100%), vegetation (Bare, Avicennia marina or Rhizophora mucronata) and immersion periods (immersion/emersion period of 12/12 h or 3/3 days just for 100%) conditions were studied for 6 months on survival and growth rates of Terebralia palustris (Linnaeus, 1767). Gastropods' activity and ecosystem engineering preformed at bare and A. marina planted cells and 3 sewage conditions (0, 20 and 60%) were determined. Survival rates were higher than 70% in all treatments. Growth rate decreased significantly with increasing sewage concentrations (mainly at unplanted conditions) and longer immersion periods. A complete shift (from immersion to emersion periods) and a significant decrease in mobility and consequently its engineer potential, due to sewage contamination, lead to a 3-4 fold decrease in the amount of sediment disturbed. Sewage contamination, primary producers' abundance and environmental conditions may have influenced the gastropods survival, growth and its ecosystem engineering potential.
Effect of initial stocking size of the predatory African sharptooth catfish (Clarias gariepinus) on recruits, growth performance, survival and yield of mixed-sex Nile tilapia (Oreochromis niloticus) in concrete tank culture system
(Springer, 2015-01-21) Samwel Mchele Limbu; Amon P., Shoko; Lamtane, Hieromin A.; Shirima, Evantuce D.; Kishe-Machumu, Mary A.; Mgana, Huruma F.; Mgaya, Yunus D.
Prolific breeding and production of high percentage of recruits are main problems in mixed-sex Nile tilapia (Oreochromis niloticus) culture in earthen ponds. The current study assessed the efficiency of different sizes of African sharptooth catfish (Clarias gariepinus) in controlling recruitment in mixed-sex Nile tilapia cultured in tanks and its effect on growth performance, percentage survival and yield. Three treatments consisting of triplicate ponds stocked with mixed-sex Nile tilapia in monoculture and in polyculture with large (62.50 ± 3.26 g) and small (40.00 ± 2.68 g) African sharptooth catfish were fed on a 297.50 g kg-1 crude protein diet for 126 days. Results showed that, the number of recruits was significantly lower in larger African sharptooth catfish predator than smaller ones and monoculture of Nile tilapia. Polyculture with larger African sharptooth catfish resulted in significantly higher growth performance of Nile tilapia. Large African sharptooth catfish in polyculture reduced the amount of small, low-value recruits, while the yield of large and high value Nile tilapia was increased. This study revealed that fish farmers can reduce prolific breeding, obtain higher growth performance and produce larger size of marketable Nile tilapia by predominantly stocking ponds with large African sharptooth catfish predator of at least 60 g.
Effect of social and economic drivers on choosing aquaculture as a coastal livelihood
(Elsevier, 2012-12-10) Slater, Matthew J.; Mgaya, Yunus D.; Mill, Aileen C.; Rushton, Steven P.; Stead, Selina M.
Aquaculture is proposed as a means to income generation and food security in developing nations. Understanding drivers of attitudes and perceptions towards choosing aquaculture as a livelihood is essential to aid policy makers in promoting its development. This paper takes a new approach to establishing a baseline of these social and economic drivers. We used simple metrics familiar to policy makers collected in face-to-face semi-structured interviews – e.g. education level, time availability to work and income level – to predict willingness of individuals to adopt aquaculture as a livelihood. We compared modelling approaches ability to provide insights into effects of social and economic factors on willingness of 422 household decision-makers in coastal villages in Tanzania to participate in sea cucumber aquaculture as an alternative livelihood. Linear regression identified the factors; time available for a supplementary livelihood, gender, social network strength and material style of life as significantly predicting individuals' willingness to adopt aquaculture. A Bayesian Belief Network (BBN) model of community data created using logistic regression results, open response analysis and critical literature appraisal allowed intuitive manipulation of factors to predict the influence of aquaculture uptake drivers and constraints. The BBN model provided quantified predictions of the effect of specific policy interventions to promote aquaculture uptake within the modelled community. The analysis from the BBN model supports its broader use as an assessment tool for informing policy formulation by highlighting key areas of intervention to increase willingness to uptake aquaculture among target groups, such as low income households and women. BBNs provide a modelling approach that allows policy makers to visualise the influence of socio-economic factors on the success of introducing aquaculture in different local contexts.
Effect of stocking density on growth, production and economic benefits of Nile tilapia (Oreochromis niloticus) and African sharptooth catfish (Clarias gariepinus) in polyculture and monoculture.
(2014-04-23) Shoko, Amon Paul; Samwel Mchele Limbu; Mrosso, Hillary Deogratias John; Mkenda, Adolf Faustine; Mgaya, Yunus D.
On-farm fish production experiments were conducted for 240 days to investigate the effect of stocking density on growth, yield and economic benefits of Nile tilapia (Oreochromis niloticus) in monoculture and polyculture with African sharptooth catfish (Clarias gariepinus). Low stocking density (LSD), medium stocking density (MSD) and high stocking density (HSD) of 30 000, 60 000 and 90 000 fish ha−1 respectively, were tested. O. niloticus cultured in polyculture attained significantly higher mean weight gain than those cultured in monoculture. O. niloticus and C. gariepinus raised together in polyculture attained significantly higher net annual yield than O. niloticus cultured alone in monoculture. Profitability analysis using partial enterprise budgets revealed that polyculture is a more profitable system than monoculture. The highest growth, yield and economic benefits were achieved at HSD and MSD than at LSD with no significant difference between HSD and MSD. Results demonstrate that farmers can achieve the highest net yield and economic benefits by culturing O. niloticus and C. gariepinus in polyculture at HSD and MSD, preferably MSD for economic reasons.

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