Environmental impacts of cage culture in Lake Victoria: the case of Shirati Bay‑Sota, Tanzania (original) (raw)
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Uganda Journal of Agricultural Sciences
Growing of fish in cages is currently practiced in Uganda and was first introduced in northern Lake Victoria in 2010. An environment monitoring study was undertaken at Source of the Nile, a private cage fish farm, in Napoleon gulf, northern Lake Victoria. In-situ measurements of key environmental (temperature, dissolved oxygen, pH and conductivity) and biological (algae, zooplankton, macro-benthos) variables were made at three transects: Transect 1-the site with fish cages (WC); transect 2-upstream of the fish cages (USC-control) and Transect 3-downstream of the cages (DSC). Upstream and Downstream sites were located approximately 1.0 km from the fish cages. Environment parameters varied spatially and temporally but were generally within safe ranges for freshwater habitats. Higher concentrations of SRP (0.015-0.112 Mg/L) occurred at USC during February, September and at DSC in November; NO 2-N (0.217-0.042 mg/L) at USC and DSC in February and November; NH 4-N (0.0054-0.065 Mg/L) at WC and DSC in February, May and November. Algal bio-volumes were significantly higher at WC (F (2,780) =4.619; P=0.010). Zooplankton species numbers were consistently lower at WC with a significant difference compared to the control site (P=0.032). Macro-benthos abundance was consistently higher at the site with cages where mollusks and low-oxygen and pollution-tolerant chironomids were the dominant group. Higher algal biomass, concentration of low-oxygen/pollution-tolerant macro-benthos and depressed zooplankton diversity at WC suggested impacts from the fish cages on aquatic biota.
Since the proliferation of cage fish farming in Uganda has raised concern over water quality deterioration, a study of the effects of cage fish farming on water quality in the Napoleon Gulf, Northern Lake Victoria was conducted during October 2012 to February 2013. Selected water column physico-chemical parameters and benthic macro-invertebrates' community parameters (i.e. numerical abundance, Shannon-Weaver diversity Index and modified Hilsenhoff Biotic Index) were analyzed monthly at both cage and non-cage sites. No significant differences were observed in physico-chemical parameter values, benthic macro-invertebrates' numerical abundance and Hilsenhoff Biotic Index between cage and non-cage sites. On the other hand Benthic macro-invertebrate species diversity differed significantly between the reference site and cage site 2 (P<0.05). Pollution tolerant Chironomus sp. and Melanoides tuberculata Muller, 1774 were significantly higher at the cage sites than the non-cage s...
Journal of Great Lakes Research, 2011
The initiation of cage aquaculture in the shallow southeast arm of Lake Malawi has raised concerns about its possible impact on the surrounding environment and the highly diverse fish community. To evaluate the impact of the cage operation on the surrounding environment, observations were made over an annual cycle in 2007 at a production capacity of~200 tonnes fish/year. Impacts of the cage wastes in the water column in the vicinity of the cages were minimal despite the substantial discharges from the cages. No significant differences were observed in concentrations of dissolved and particulate nutrients (ammonia, nitrate, phosphate, particulate C,N and P), chlorophyll, chlorophyll fluorescence, dissolved oxygen, total suspended solids, Secchi depths and extinction coefficient of photosynthetically active radiation between the cage site and the control stations upstream or downstream of the fish farm. Although sedimentation rates measured in traps were higher under the cages than at control sites, the sediment flux was a small percentage of total feeds added to the cages. Apparently cage wastes were efficiently dispersed by water currents which averaged 9.3 cm/s below the fish cages. Consumption of the wastes by wild fish species which aggregated around the fish cages and their movement in the vicinity of the cages also contributed to the dispersion of the cage wastes and served to dilute impact of the cages. In combination, these physical and biological processes reduced the immediate impact of the cage farming operation and must be considered in the siting of future cage farms.
International Journal of Fisheries and Aquatic Studies, 2016
Since the proliferation of cage fish farming in Uganda has raised concern over water quality deterioration, a study of the effects of cage fish farming on water quality in the Napoleon Gulf, Northern Lake Victoria was conducted during October 2012 to February 2013. Selected water column physicochemical parameters and benthic macro-invertebrates’ community parameters (i.e. numerical abundance, Shannon-Weaver diversity Index and modified Hilsenhoff Biotic Index) were analyzed monthly at both cage and non-cage sites. No significant differences were observed in physico-chemical parameter values, benthic macro-invertebrates’ numerical abundance and Hilsenhoff Biotic Index between cage and noncage sites. On the other hand Benthic macro-invertebrate species diversity differed significantly between the reference site and cage site 2 (P<0.05). Pollution tolerant Chironomus sp. and Melanoides tuberculata Muller, 1774 were significantly higher at the cage sites than the non-cage sites (P<...
Impacts of cage culture on physico-chemical and bacteriological water quality in Lake Volta, Ghana
African Journal of Aquatic Science, 2016
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.
Bonorowo Wetlands, 2018
Mensah VF, Yemoh T, Ofori BD. 2018. Environmental and socioeconomic impact of cage aquaculture at Kpeve Tornu section of the Volta Lake. Bonorowo Wetlands 2: 84-95. Sufficient data on the financial viability of cage aquaculture in Ghana is limited, and only little is also known of the effects of fish farming on the Volta Lake on fishing communities. This study, therefore, sought to investigate these relevant issues at Kpeve Tornu, a fishing society in Afadjato South District in the Volta Region. Laboratory analysis of physicochemical parameters suggested that there were no significant differences between water quality parameters from four fish farms and two control locations. A cost-benefit analysis performed on five cages of volume 360 cubic meters each was 1.34 in the first production cycle, whereas a gross margin of 104.41 percent in the second production cycle suggesting that cage aquaculture industry in Ghana was financially viable. The cage aquaculture industry also impacted p...
Aquaculture, 2011
The potential impact of Nile Tilapia (Oreochromis niloticus) cage culture on water quality and pelagic community composition was investigated in two Ethiopian small water bodies, one located in the highlands (Yemlo) and the other in the Great Rift Valley (Allage). This study was designed to assess the difference between the cages and open water in relation to those water quality changes attributable to intensive inputs of fish waste and left-over fish feed. All physico-chemical water quality parameters including inorganic nutrients varied temporally, coupled with dry and wet periods. The reservoir's trophic state ranged from eutrophic to hypereutrophic, with a strong correlation between chlorophyll-a and total phosphorus. The phytoplankton community was dominated by Cyanobacteria (84% of total phytoplankton abundance), in particular by Anabaenopsis sp. in Allage reservoir, whereas Chlorophyta (70%), with Pediastrum simplex as the dominant taxon, prevailed in Yemlo reservoir. A total of 23 zooplankton taxa were recorded during our sampling; rotifers were the richest group with 14 taxa distributed in 6 genera, followed by cladocerans represented by 6 taxa (5 genera) and copepods by 3 taxa (1 genus). Dissolved inorganic nutrient concentrations and other physical parameters showed no significant differences between the cages and open water. The exceptions were dissolved oxygen and ammonium nitrogen, which were lower and higher in the cages, respectively. For the whole study period of 240 days, the mean net weight and daily growth rate per fish were 183.3 g and 1.1 g d − 1 , respectively.
Impact of Cage Aquaculture on Water Quality Condition in Lake Maninjau, West Sumatera Indonesia
2015
Water quality characteristic of Lake Maninjau related to the deterioration condition has been intensively reported, nevertheless research on water quality as an impact of cage aquaculture level has never been done. The aim of this research was to identify influence of cage density to water quality condition. The study was conducted at 11 stations in Lake Maninjau, by measuring 11water quality parameters at a depth of 4.5m and sediment organic content on locations that have soft substrate. Measurement periods were on June 2013, September 2013, December 2013, and March2014. Activity of cage aquaculture was distributed in all over the lake shore lines, with the highest density at 1226 units km-1. Water quality measurement indicated similar condition based on spatial patterns (degree of similarity >85%) with tendency that the increase number of cages influence several parameters including increase concentration of chemical oxygen demand (COD), total nitrogen, and ammonium; and decrea...