7 research outputs found
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NON-NATIVE FISH SPECIES AS AN IMPORTANT PART OF ZAMBIA'S FOOD SYSTEM: A CASE STUDY OF THE LAKE KARIBA FISHERY
Fish have an important role in food systems of Zambia and are a cheaper source of animal protein, vitamins and minerals. Presently, fish catches are dwindling and many children and women in rural Zambia are malnourished because their diet consists mainly of maize, vegetables and legumes. The main component of the diet is nsima, a form of thick porridge prepared from maize flour, which provides energy as carbohydrates. This study was done to assess the impact of a nonnative fish species (Oreochromis niloticus, Nile tilapia) which has both positive and negative impacts on Zambia’s food system, with particular reference to the Lake Kariba fishery. The study was based on a networked systems framework, achieved through the administration of questionnaires, interviewing 377 randomly selected respondents from the three areas of the lake (I, II and IV) and 156 respondents from 7 selected open fish markets. Focus group discussions (FGD) were done with women, men and youth, who were key informants. Analysis of results using chisquare analysis, which cross-tabulated variables were used to obtain the results. Non-native fish were introduced in the early 1980s for cage culture production in Lake Kariba but some fish accidentally escaped. This has changed the composition and abundance of fish species in the lake. Despite the negative ecological impact on native biodiversity, results showed that more fish are available to households, improving nutrition and disposable income from fish sales. The disposable income is used to purchase other foods, thereby reducing malnutrition among rural households. Thus, the introduction of appropriate non-native species might benefit households and the nation as a whole
Effects of common carp and African catfish on plankton, periphyton, benthic macroinvertebrates in pond ecosystem
As the common carp Cyprinus carpio and African catfish Clarias gariepinus affect biotic assemblages in aquatic ecosystems through their benthivory, their introduction has been considered an environmental concern. We compare the effects of common carp and African catfish on adjacent trophic level assemblages of plankton, periphyton, benthic macroinvertebrates and native tilapia in a pond ecosystem at the National Aquaculture Center, Zomba, Malawi. Four treatments were involved in the study: ponds with common carp (T1), ponds with African catfish (T2), ponds with both common carp and African catfish (T3), and ponds lacking both common carp and African catfish (T4). In all treatments, the endemic Shire tilapia Oreochromis shiranus was also present as part of the local macrofauna. Results showed that T1 had the most abundant phytoplankton but the lowest periphyton, zooplankton and benthic macroinvertebrate abundance and diversity. T4 had the least phytoplankton but the most abundant and diverse zooplankton, periphyton and benthic macroinvertebrates. There was no significant difference between T2 and T3 (both intermediate to T1 and T4) in terms of phytoplankton, periphyton and benthic macroinvertebrate abundance and diversity. Better water quality regime and increased biomass of native tilapia fish were observed in T3 ponds. We conclude that the farming of common carp in aquatic ecosystems containing African catfish may not adversely affect the environment and that the polyculture of African catfish and common carp can be adopted as a management strategy to mitigate the potential adverse effects of common carp
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MORPHOMETRIC VARIATIONS AMONG OPSARIDIUM MICROLEPIS (GÃœNTHER, 1864) FROM LAKE MALAÅ´I MIGRATING TO DIFFERENT RIVERS FOR BREEDING
Fish is an important resource in Malawi as a source of food for the majority as it provides affordable source of dietary animal protein as well as income. A number of fish species in the Malawi water bodies have their population dwindling. One of the species under serious threat of extinction is the Opsaridium microlepis - a potamodromous fish species that migrate to the rivers during its spawning period and its management seems a nightmare. A number of studies reveal contrasting results on genetic makeup and morphological aspect of this fish species. With changes in the ecosystems of the rivers connecting Lake Malawi, coupled with absence of strong management measures in the major rivers adjoining the lake, problems have arisen in the conservation of potamodromous fish species. This necessitated the present study to investigate if the morphological features of stocks of O. microlepis are the same or not and if they have changed to adapt to changes in the ecosystems. One hundred and eleven O. microlepis fish samples were collected from Linthipe River (48), Bua River (59) and North Rumphi River (4) monthly from March to August 2020 using trawled and static gillnets. Twenty-four morphometric characteristics were measured to determine if any morphological differences existed among the fish samples from the three rivers. Principal component analysis (PCA) was used to compare morphology of the fish. Results of the study showed no significant morphological differences among stocks from the three rivers, implying that O. microlepis in these rivers belong to same stock morphologically. The study reveals that the species do not differ morphologically even though they migrate to different rivers for breeding. The study further notes that numerous activities taking place along the tributary rivers (as observed during the study) such as modification of fishing gears as well as fishing methods and the deterioration of the spawning grounds due to siltation from soil erosion caused by deforestation and agriculture, are putting the potamodromous fish species such as O. microlepis under serious threat. The study recommends that the populations of O. microlepis from the rivers can be managed equally since they are morphologically similar. Adopting uniform catchment management and sustainable exploitation of O. microlepis (such as regulations on mesh sizes and fishing methods, closing the rivers from fishing activities during spawning period, river bank and catchment management and restoration) with the aim of conserving the stocks from further overexploitation in these rivers is recommended so that the communities and the people at large continue to utilize the resource sustainably and at the same time, sustaining their livelihood