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Large lakes throughout the world offer development opportunities for cage aquaculture. However, due to their vast area, identifying the most suitable locations can be a challenge. This is also complicated as lake systems are often multi‐use environments, so a strategic approach to managing the resource is required. This study uses geographic information systems (GIS) to develop a broad‐scale approach that identifies potential areas that may be suitable for cage aquaculture development. Volta Lake, one the world's largest man‐made lakes, is used as a case study. The overall GIS model combines four sub‐models, bathymetry, hydrography, water quality and access, and a constraints layer, to identify the most suitable locations for tilapia production. Three different cage sizes are modelled: small, medium and large. The model outputs suggest that approximately 102 km2 (1.7%), 406 km2 (6.9%) and 407 km2 (6.9%) of Volta Lake can be categorized as highly suitable for development of small, medium and large cages respectively. A further 634 km2 (10.8%), 1264 km2 (21.4%) and 1055 km2 (17.9%) can be categorized as suitable for the same. The results can be used by stakeholders and decision makers to identify specific areas where aquaculture development for cage farming of tilapia could be prioritized.

Over the past decade, the aquaculture sector in Ghana has experienced tremendous growth—driven mainly by large-scale cage aquaculture. Pond aquaculture, traditionally extensive and with limited external inputs, has been transforming over the same period. Farm profitability was wide-ranging, between −12.00 and 46.00 Ghanaian cedi (GHC) per square meter (m2), with an average of GHC 8.82/m2 for farmers active in 2019. Despite wide variability in production and profits, the majority of farmers experienced positive profits—on average, GHC 3.24 per kilogram of tilapia produced, or a 27% profit margin. Farmers who adopted good aquaculture practices and intensified their production have high productivity and positive profits. Nonetheless, the cost to produce 1 kg of tilapia in Ghana (roughly US$1.51 on average) was much higher than in other major tilapia-producing countries (averaging roughly US$0.78 to 1.29). COVID crisis further affected fish farmers: 54% experienced difficulties in accessing inputs, 56% experienced difficulties selling their fish, and farmgate fish prices went down in April–August, although slowly bounced back by end of 2020. Improving the competitiveness and resilience of Ghanaian tilapia sector will require improved seed, increased adoption of good management practices, lower-cost quality feed, and enabling policies and regulations.

Over the past decade, the aquaculture sector in Ghana has experienced tremendous growth—driven mainly by large-scale cage farms—but it has been unclear how the rural poor have shared in this growth. A research project has been initiated to help diagnose, design, and test interventions for better inclusion of the rural poor, women, and youth in the tilapia value chain. This report describes the baseline data on 603 small-scale tilapia farmers in Ghana. The data collected during two-hour face-to-face interviews during May–July 2019 are disaggregated by socioeconomic indicators, gender, and age group. Baseline data show that 9 percent of farm managers and owners were women, and an additional 9 percent of farms engaged women in some decision-making. Moreover, women contributed 16 percent of family labor and 5 percent of hired labor on farms. Youth represented 14 and 24 percent of owners and managers, respectively, but contributed 68 percent of the total family and hired labor on farms. A large majority of managers and owners had at least high school education, with a third of owners and a quarter of managers attaining at least a college degree. In Brong Ahafo and Ashanti regions especially, most farmers engaged mainly in crop farming and non-farm businesses as their main livelihood, with fish farming as a small contributor to overall household income and livelihood. Farmers in all regions had poor record-keeping and management practices and low compliance with sanitation, fish health, and food safety standards. A wide variety of input usage, management practices, and performance was observed among fish farms. As a result, the profitability of fish farms was also wide-ranging, between –12.00 and 46.00 cedi per m2, with an average of 8.82 cedi per m2. Despite wide variability in production and profits, the majority of farmers experienced positive profits. On average, a farmer received a profit of 2.4 cedi per kilogram of tilapia produced or a 27 percent profit margin. These encouraging figures indicate that farmers who adopt good aquaculture practices can achieve respectable profits.

Globally, aquaculture production is faced with numerous challenges, notable among which is water quality. The study determined seasonal environmental changes in Lake Volta and its implications on cage production of Nile tilapia, Oreochromis niloticus in experimental and commercial farm (Sun Woo Farm) set-ups. For each set-up, three cages were used, each measuring 81 and 162.5 m3 for experimental and commercial, respectively. The cages were stocked with 22.5 g fingerlings at a rate of 40 and 80 m−3 in experimental and commercial cages, respectively, and fed commercial diet. The growth performance, yield, economics, and selected water quality parameters were monitored during the dry and wet seasons between November 2014 and July 2015. There were no differences in water quality parameters between dry and wet seasons (p > 0.05). Water quality for both seasons remained within limits required for good Tilapia growth in both set-ups. There were minimal variations in growth characteristics between seasons which were not significant; however, final mean weight and yields were high in the dry seasons in both set-ups. The cost of feed and fingerling accounting for about 80% of total costs were the major components identified to affect cost of production. A higher profit index and returns on investment were observed in the dry season in both set-ups and was linked to higher survival rates in the season. Production of Nile tilapia in cages can be cultured throughout the year without any adverse effects as exhibited in similar production patterns in both experimental and commercial set-ups.

Fish species assemblage and selected environmental variables were monitored in Lake Volta from September 2014 to August 2016 to determine seasonal variability in species composition, catch and environmental variables that determine the structure of the fish community. A total of 1,557 individual fish belonging to 41 species, 25 genera and 13 families were recorded. The important fish species with respect to frequency of occurrence, abundance and weight, respectively, were as follows: Chrysichthys (100%; 43.03%; 17.93%), tilapias (100%; 28.97%; 17.86%), Alestes (100%; 14.13%; 32.10%) and Bagrus (91.67%; 5.65%; 12.80%) in that order. The composition of fish species and their temporal variation in experimental catches were similar to that of commercial catches. There were no significant differences (p > 0.05) in species abundance, weight and diversity indices between the dry and wet seasons. The modal class of length frequency distribution of the dominant species in the catch, Chrysichthys, reduced from 125 mm in 2006 to 95 mm in the current study indicating overfishing. Environmental variables considered showed little variation and within optimal ranges for fish survival and did not differ significantly between seasons. Canonical Correspondence Analysis showed that environmental variables explained 43.30% of the variation in species abundance with Lake water level, nitrite-nitrogen and total dissolved solids being the main environmental factors influencing the structure of the fish community.

The extent to which statistical bias-adjusted outputs of two regional climate models alter the projected change signals for the mean (and extreme) rainfall and temperature over the Volta Basin is evaluated. The outputs from two regional climate models in the Coordinated Regional Climate Downscaling Experiment for Africa (CORDEX-Africa) are bias adjusted using the quantile mapping technique. Annual maxima rainfall and temperature with their 10- and 20-year return values for the present (1981–2010) and future (2051–2080) climates are estimated using extreme value analyses. Moderate extremes are evaluated using extreme indices (viz. percentile-based, duration-based, and intensity-based). Bias adjustment of the original (bias-unadjusted) models improves the reproduction of mean rainfall and temperature for the present climate. However, the bias-adjusted models poorly reproduce the 10- and 20-year return values for rainfall and maximum temperature whereas the extreme indices are reproduced satisfactorily for the present climate. Consequently, projected changes in rainfall and temperature extremes were weak. The bias adjustment results in the reduction of the change signals for the mean rainfall while the mean temperature signals are rather magnified. The projected changes for the original mean climate and extremes are not conserved after bias adjustment with the exception of duration-based extreme indices.

The study determined the impacts of fish cage farming on the gorge area of Lake Volta. Water and sediment samples were collected from six sites in the Lee Cage Farm; four from sections with cages and two from about 1300 m upstream of the farm which served as the control. Water quality variables monitored were pH, temperature, dissolved oxygen, nitrate-nitrogen, ammonia-nitrogen, orthophosphate, faecal coliforms and total coliforms. Variables monitored in the sediment were organic matter, total carbon, total nitrogen and total phosphorus. There were variations in water quality between the farmed and control sites but the differences were not significant (p > 0.05). The mean counts of total coliform in the water ranged from 940 - 3318 cfu/100 ml while faecal coliforms ranged from 113 - 552 cfu/100 ml at the farmed site. The mean total coliform count at the control site ranged from 837 - 6960 cfu/100 ml while the faecal coliforms ranged from 48 - 120 cfu/100 ml. Therefore, there was significant variation between the faecal coliforms count at the two sites (p = 0.046). The results suggest that the general microbiological quality of the water at the study area was unacceptable.

Climatic changes influence the thermal and oxygen dynamics of a lake and thus its ecological functioning. The impacts of climatic changes on tropical lakes are so far poorly studied and the extent of the effects is therefore uncertain, most investigations describing only potential effects. In this study, we applied the one-dimensional lake ecosystem model GOTM-ERGOM to quantify the effects of climate change on thermal stratification, oxygen dynamics, and primary production in meso-oligotrophic lake Volta. GOTM-ERGOM was calibrated and validated using two years of observed data. The validated model was used to evaluate a series of future climate change scenarios. The model simulations showed good agreement with observed water temperature, dissolved oxygen and chlorophyll-a and indicated intensified stratification and reduced oxygen levels in the productive water layers of the lake. However, the longer-lasting stratification (prolonged stability) did not translate into permanent stratification. A relatively small (1 m) upward shift of thermocline depth resulted in an 8%-12% volume loss of the oxygen-rich upper mixed layer, which may be significant for the fisheries of the lake as it diminishes the size of suitable fish habitats. Light limitation of primary production renders the lake somewhat resilient to intensive algae blooms, as traceable in both the present and in the future climate scenarios. In the long term, the ongoing climate change may affect riparian communities that depend on the lake's fisheries for their livelihood. In consequence, future lake management strategies for implementation need to account for the impacts of future climate change. (C) 2018 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.

A mass balance model of trophic interactions among ten key functional producer and consumer groups in Lake Volta was constructed using the Ecopath model to study the energy flows and species interactions in the lake. The present study was based on secondary and primary data on fish catch, diet composition, phytoplankton and zooplankton biomasses, collected in 2015 and 2016. Additional information on growth parameters of major species required for balancing the Ecopath model was obtained from sampling and FishBase. The functional groups were detritus, phytoplankton, zooplankton, benthos, prey fish, Tilapia, Bagrus, Chrysichthys, Alestes and Synodontis species. Four trophic levels were identified in the Lake Volta ecosystem, with the energy flow occurring mainly within the first three trophic levels. The calculated ecotrophic efficiency value of the primary producers (phytoplankton: 0.17; detritus: 0.22) indicated they were least exploited, compared to the secondary producers, zooplankton (0.80) and benthos (0.50). All secondary consumers had ecotrophic efficiency values higher than the primary producers, indicating they are exploited in the ecosystem. The main energy flows in the lake were from phytoplankton and detritus at trophic level I, and Bagrus species, the top predator, at a level of 3.30. The network analysis, illustrating a connectance index of 0.43 and an omnivory index of 0.06, in the lake system indicated the ecosystem is unstable, somewhat immature and still in a developing stage.

The effects of cage fish farming on physico-chemical and bacteriological water quality in Lake Volta, Ghana, were investigated in 2013–2014. Farmed and unfarmed (control) areas of the lake were selected for monitoring. Nutrients, temperature, dissolved oxygen, conductivity, turbidity, pH, total coliforms, Pseudomonas and Vibrio spp. in the water were monitored monthly. Analyses of the water samples were carried out according to standard procedures. Physico-chemical quality of the water in both farm and control sites were within ranges typical of minimally impacted water and did not vary significantly between the two contrasting sites. The bacteriological analysis, however, revealed contamination of the lake water by fish farming. The bacterial counts at the farmed sites were significantly higher (p < 0.05) than those of the control sites, with figures at the farmed sites ranging from 132 to 1 708 cfu 100 ml−1 for total coliforms, 514 to 5 170 cfu 100 ml−1 Pseudomonas spp. and 14 to 516 cfu 100 ml−1 for Vibrio spp. The results suggested that cage fish farming has increased bacterial loads in the lake water, but has had minimal impact on its physico-chemical quality.Keywords: aquaculture, contamination, fish farming, large lake, pollution

Aquaculture is a preferred alternative to increasing global fish production than management of wild stocks. Its practice is, however, known to have ecological impacts if not managed well. The study was conducted to determine the potential impact of cage culture of fish on food preference of wild fish. A case study was carried out in the Volta Lake at Kpeve-Tornu using Chrysichthys species which is one of the dominant species found in the Lake. Sampling was done for eight months from August 2013 to March 2014. An area of the lake with no fish farming activities was used as a control. The stomachs of 130 Chrysichthys specimens were analyzed. Importance of each food item was determined using frequency of occurrence method. The dominant food items identified were chironomid larvae and detritus; occurring in 27.3% and 36.4% respectively of the stomach contents at the cage culture site and 63.9% and 52.8% at the control site respectively. Plant parts also occurred in 36.4% of the stomachs at the cage culture site. Lampsilis species, a freshwater mussel, was found only in the stomachs at the control site and it occurred in 41.7% of them. Cage culture in the Volta Lake impacted on the food preference of Chrysichthys species by influencing the availability and abundance of food items. As promising as cage culture is in Ghana; in supplementing production from capture fisheries, it must be done on a scale that keeps its ecological impacts in the Volta Lake in control.

The Weija Reservoir is an important resource for the production and supply of potable water, fish and irrigation services in Ghana. The study was undertaken to estimate the potential fish yield of Weija Reservoir to provide information for planning and management and to address the challenges of paucity of information on the potential fish yield of reservoirs in Ghana. Fish and water samples were collected monthly between March and December 2011 at Intake, Machigeni and Galilea sampling stations in the Weija Reservoir. Based on the physico-chemical parameters evaluated, the Weija Reservoir is adequate for fish survival, growth and production despite indications of low levels of organic contamination. Estimates of mean fish yield and potential fish yield for the three (3) stations based on morpho-edaphic index indicate that Machigeni has the highest yields followed by Intake and Galilea due to differences in anthropogenic activities, contamination and species richness. Monthly variations in potential fish yield and physico-chemical parameters follow similar pattern at all three sites with Machigeni recording the highest values and Intake the lowest. For the section of the reservoir sampled, the mean potential fish yield was 68.27 kg ha -1 while the mean fish yield was 229.45 t yr -1 giving indication of declining fish yield compared to the earlier life of the reservoir which is attributable to physico-chemical, environmental, biological and anthropogenic changes. For successful fisheries management, regular monitoring of the fish species as well as control of fish habitat and environmental degradation are recommended.

The speciation of cadmium, lead, copper, zinc, manganese and iron into exchangeable, carbonate, reducible and organic bound fractions was studied in sediments from coastal and freshwater environments in Ghana. This was relevant as the species in which metals are stored within specific sediment components is important in determining their impact on the environment. For both coastal and inland sediments, a higher percentage of cadmium was associated with the more available exchangeable and carbonate fractions, while iron, zinc and manganese were mainly associated with the reducible and organic fractions. Lead and copper were found to have the greatest ability to form different species in the samples examined and were more evenly associated with all the fractions. The metals generally showed more ability to form different species in inland freshwaters than in coastal relatively saline waters. However, differences between inland and coastal waters were based more on whether the environments were oxidising or ...

Sakumo Lagoon, situated near Accra, is a Ramsar-listed coastal wetland threatened by urban and agricultural waste, being located in an urban area where access to domestic and waste disposal facilities is a major problem. The aim of this study was to assess the pollution status as well as trends, in terms of pollution laoding, in the lagoon. Nutrients, dissolved oxygen, biochemical oxygen demand, suspended solids, temperature, pH and faecal coliforms were monitored on a quaterly basis from 1997–1998 and 2001–2002, covering both wet and dry seasons. Significant increases in the mean concentrations of suspended solids, ammonia-nitrogen, phosphate-phosphorus and biochemical oxygen demand indicated an increase in the level of pollution in the lagoon. Faecal coliform counts were fairly high, exceeding 130 counts 100 ml–1, which is the maximum acceptable count in Ghana for water used for recreation. Results from the study suggested rapid deterioration of the lagoon water quality between 1997 and 2002. Domestic a...

The pollution status of Sakumo II and Muni Lagoons and Mamahuma and Gbagbla Ankonu feeder streams, which feed Sakumo II along the coast of Ghana, were assessed and compared. As expected of saline waters, pH values of both lagoons fell within a slightly neutral to saline range whilst, the feeder streams were moderately saline. Conductivity distribution also showed saline (>5.0 mS cm−1) characteristics of the lagoons, while, the feeder streams are brackish (1.5–5.0 mS cm−1). DO concentrations in both lagoons indicated a wide variation. Relatively high BOD and nutrients content of Sakumo II and the feeder streams suggested that, Sakumo II and its feeder streams are moderately to grossly polluted. However, Muni Lagoon was characterized by relatively low BOD and nutrients content suggesting relatively low anthropogenic impact. The ionic dominance patterns for Sakumo II and Muni Lagoons were: Na+ > Mg2 + > Ca2 + and Cl− > HCO3− > SO42−, Na+ > Ca2 + > Mg2 + and Cl− > HCO3− > SO42−, respectively. Using water quality index (WQI), Sakumo II was found to be grossly polluted and requires mitigation measures, while, Muni Lagoon was of fairly good quality and requires monitoring.

Trace metal (Cu, Zn, Pb, Mn, Fe and Cd) levels were determined in water and sediment from the Sakumo II and Muni lagoons and the Mamahuma and Gbagbla Ankonu feeder streams, which feed the Sakumo II lagoon over a 1-year period, and their occurrences compared. Some physical parameters (temperature, pH and electrical conductivity) were also investigated. The aim of the study was to establish the pollution status of the two lagoons, as well as investigate whether the feeder streams of the Sakumo II lagoon have any influence (in terms of trace metal pollution) on the Sakumo II lagoon. Results showed that upper mean values in water and sediment were Zn ( 0.160 ± 0.01 mg/l, 48.7 ± 0.93 mg/kg), Pb (0.057 ± 0.03 mg/l, 29.2 ± 3.2 mg/kg), Mn (0.798 ± 0.07 mg/l, 668.2 ± 6.3 mg/kg), Cu (0.158 ± 0.01 mg/l), Fe (1.32 ± 0.73 mg/l, 3075 ± 14.7 mg/kg), respectively, for Sakumo II lagoon. Cd levels in water and sediment ranged from 0.004 ± 0.001 to 0.009 ± 0.001 mg/l and < 0.002 to 0.88 ± 0.05 mg/kg respectively, in the Sakumo II lagoon. Compared to the maximum contaminant level (MCL) of 0.005 mg/l, the Cd levels in water from the Sakumo II lagoon may be detrimental to the ‘health’ of the aquatic ecosystem and, consequently, consumers of fish products from the Sakumo II lagoon. Water and sediment in the Muni lagoon had trace metal concentrations with upper mean values as Cd (< 0.002 mg/l, 0.325 ± 0.01 mg/kg), Pb (0.033 ± 0.01 mg/l, 1.46 ± 0.18 mg/kg), Mn (0.434 ± 0.02 mg/l, 63.8 ± 1.50 mg/kg), Zn (0.077 ± 0.001 mg/l, 13.7 ± 0.18 mg/kg), Cu (0.013 ± 0.001 mg/l) and Fe (1.085 ± 0.26 mg/l, 3198.4 ± 3.51 mg/kg), respectively. Generally, trace metal levels detected in sediment from the Mamahuma ( Zn: 10.4 ± 4.10 mg/kg, Pb: 10.6 ± 1.84 mg/kg, Mn: 63.7 ± 4.5 mg/kg, Fe: 7487 ± 23.5 mg/kg, Cd: < 0.002), and from the Gbagbla Ankonu ( Zn: 155 ± 13.9 mg/kg, Pb: 37.4 ± 3.07 mg/kg, Mn: 298.2 ± 2.5 mg/kg, Fe: 3209 ± 50.5 mg/kg, Cd: 0.70 ± 0.05 mg/kg) feeder streams were relatively higher than those in the Sakumo II lagoon. Sediment from the feeder streams, therefore, provided a deeper insight into the long- term pollution state of the feeder streams and, consequently, the Sakumo II lagoon. The streams could, thus, be described as potential sources of trace metal pollution to the Sakumo II lagoon. Trace metal levels were also found to be more concentrated in sediment from the mid-section of the Muni lagoon than those from the northern and southern sections, while the northern section had more trace metal concentrations in water than those from the mid- and southern sections. The study also showed that trace metal levels detected in both water and sediment from the Sakumo II lagoon were higher relative to those from the Muni lagoon. The Sakumo II lagoon could be described as relatively more polluted with trace metal load.

An assessment was conducted on the concentrations of zinc, copper, manganese, iron, lead and cadmium in 10 different fish species caught from some coastal and inland waters in Ghana, as part of a project on monitoring of pollution in water bodies in Ghana. Shellfish species (Egeria paradoxa galanata and Atya gabonensis) caught from inland waters had higher elemental concentrations than those caught from coastal waters. Mean concentrations of Fe and Mn were higher in E. paradoxa galanata, A. gabonensis and Trachiurus trachiurus, while Panulirus regius and Sardinella eba had higher mean concentrations of Cu. T. trachiurus, Dentex congoensis and T. ovatus had higher mean concentrations of Pb, while T. trachiurus and S. eba had higher mean concentrations of Zn. Mean Cd concentrations in the fish species were relatively low, with mean concentrations of Cynoglossus cadenati, D. congoensis and T. ovatus below detection limits. The mean concentrations of Zn, Cu, Pb and Cd for shell fishes were comparable to those obtained from previous studies in Ghana. However, they were lower than those reported in other areas of the sub-region. The mean concentrations of Zn, Cu, Pb and Cd in fin fishes were higher than those obtained from previous studies in Ghana. However, these values were comparable to those obtained from other areas in the sub-region. Compared to WHO limits, the levels of Zn, Pb, Cu and Cd in the fish species were lower, and, therefore, safe for human consumption. The study also showed that all the fish species except S. eba, Solar crumophthalmus and P. regius are safe for human consumption with respect to Zn, Cu and Fe. West African Journal of Applied Ecology Vol. 13 2008: pp. 27-38

A quantitative assessment of air, water and land-based sources of pollution to the coastal zone of the Accra-Tema Metropolitan Area of Ghana was conducted by making an emission inventory from information on industrial, commercial and domestic activities. Three sources of air pollution were analysed, viz, emission from mobile combustion engine sources, stationary combustion sources and industrial processes. The mobile combustion sources were the largest contributors to air pollution. Concerning water pollution, 15 industrial types were investigated. The Food and Beverage industry accounted for more than 80% of the total waste volume discharged per annum. The major rivers collectively contributed more water pollution loads to the coastal zone than the industrial effects. They, however, have less negative effect. Solid waste loads, mainly in the form of dry solids and sludge, from 16 industrial types, commercial and domestic sources were computed. Commercial and domestic activities accounted for more than 50% of the solid waste load discharged per annum. About 40% of waste sludge is discharged into drains; some are incinerated, while others are disposed off by land filling. (Journal of the Ghana Science Association: 2001 3(3): 126-135)