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Sustainable agriculture intensification is an urgent challenge in developing countries including Tanzania. One potential solution is to adopt farming systems that increase farm production by optimizing resource use efficiency, and integrated aquaculture system, which involves farming of fish and crops, is an example of such systems. This study investigated the impact of Integrated agriculture and aquaculture (IAA) farming on water use efficiency, fish and vegetable production and overall system profitability, and how these parameters are affected by fish stocking densities. Oreochromis niloticus (2.5 g average initial weight) were cultured at low stocking density (five fish m−3, LSD), medium stocking density (eight fish m−3, MSD), and high stocking density (12 fish m−3, HSD) for 205 days. Brassica rapa pekinensis and Amaranthus hybridus cultivated adjacent to the fish tanks were irrigated with; (i) fish tank water, without any fertilizer inputs; (ii) fish tank water, partially fertilized; (iii) tap water, fully fertilized (farmers’ practice); and (iv) tap water without any fertilizer inputs. Although the use of tank water from the high fish stocking density resulted in significantly higher vegetable yield, high fish stocking resulted in lower fish growth, profitability and water use efficiency compared to the other fish stocking densities, probably because of low survival rates (28%) at high stocking densities. The integration of fish at a medium stocking density with vegetables resulted in significantly higher net income than when fish and vegetables were grown separately.

Growth performance of 120 fi sh fi ngerlings of Tilapia sparmanni stocked in three rectangular tanks was evaluated after feeding on three different formulated chicken feeds for eight weeks. Fish wet weights and lengths were measured after every two weeks, they indicated considerable increase.

Lake Tanganyika, the largest tropical freshwater lake and the second largest by volume on Earth is characterized by strong oxygen and redox gradients. In spite of the majority of its water column being anoxic, Tanganyika hosts some of the most diverse and prolific fisheries and ecosystems on Earth. Yet, little is known about microorganisms inhabiting this lake, and their impacts on biogeochemistry and nutrient cycling underlying ecosystem structure and productivity. Here, we apply depth-discrete metagenomics, single-cell genomics, and environmental analyses to reconstruct and characterize 3996 microbial genomes representing 802 non-redundant organisms from 81 bacterial and archaeal phyla, including two novel bacterial candidate phyla, Tanganyikabacteria and Ziwabacteria. We found sharp contrasts in community composition and metabolism between the oxygenated mixed upper layer compared to deep anoxic waters, with core freshwater taxa in the former, and Archaea and uncultured Candidate Phyla in the latter. Microbially-driven nitrogen cycling increased in the anoxic zone, highlighting microbial contribution to the productive surface layers, via production of upwelled nutrients, and greenhouse gases such as nitrous oxide. Overall, we provide a window into how oxygen gradients shape microbial community metabolism in widespread anoxic tropical freshwaters, and advocate for the importance of anoxic freshwater habitats in the context of global biogeochemical cycles and nutrient cycling.

The distribution and some biological characteristics of commercially important giant sea catfish, Arius thalassinus (Rüppell, 1837) were studied in Mafia Island from October 2010 to October 2011. Samples were collected from artisanal fishing gear, mainly longlines, sharknets and ringnets, which yielded a total of 2,723 kg comprising 756 A. thalassinus individuals with the largest specimen measuring 1,000 mm TL. The species occurred only on the western coast of Mafia Island with the highest catch rate of 19.3 kg/fisher/day in March when murky water predominates. The reproductive biology of A. thalassinus was investigated to infer its vulnerability to fishing. A. thalassinus reached size-at-first maturity at (LM50 = 520 mm TL) and exhibited lower mean (± s.e.) batch fecundity of 65.6 ± 3.37 eggs per female of size range 605 – 970 mm TL comprising large-sized hydrated oocytes with mean (± s.e.) diameter of 15.2 ± 0.12 mm. A. thalassinus spawned once in a year during February and April under heavy precipitation conditions (124 - 499 mm). We therefore conclude that restricted distribution, large-bodied size, lower fecundity, late maturation, and reported high trophic level signify that A. thalassinus is potentially vulnerable to fishing pressure. It is therefore recommended to restrict fishing A. thalassinus during spawning season for its sustainability.

International audience; Climate change is affecting lake stratification with consequences for water quality and the benefits that lakes provide to society. Here we use long-term temperature data (1970–2010) from 26 lakes around the world to show that climate change has altered lake stratification globally and that the magnitudes of lake stratification changes are primarily controlled by lake morphometry (mean depth, surface area, and volume) and mean lake temperature. Deep lakes and lakes with high average temperatures have experienced the largest changes in lake stratification even though their surface temperatures tend to be warming more slowly. These results confirm that the nonlinear relationship between water density and water temperature and the strong dependence of lake stratification on lake morphometry makes lake temperature trends relatively poor predictors of lake stratification trends.

Lake Tanganyika, the deepest and most voluminous lake in Africa, has warmed over the last century in response to climate change. Separate analyses of surface warming rates estimated from in situ instruments, satellites, and a paleolimnological temperature proxy (TEX86) disagree, leaving uncertainty about the thermal sensitivity of Lake Tanganyika to climate change. Here, we use a comprehensive database of in situ temperature data from the top 100 meters of the water column that span the lake’s seasonal range and lateral extent to demonstrate that long-term temperature trends in Lake Tanganyika depend strongly on depth, season, and latitude. The observed spatiotemporal variation in surface warming rates accounts for small differences between warming rate estimates from in situ instruments and satellite data. However, after accounting for spatiotemporal variation in temperature and warming rates, the TEX86 paleolimnological proxy yields lower surface temperatures (1.46 °C lower on average) and faster warming rates (by a factor of three) than in situ measurements. Based on the ecology of Thaumarchaeota (the microbes whose biomolecules are involved with generating the TEX86 proxy), we offer a reinterpretation of the TEX86 data from Lake Tanganyika as the temperature of the low-oxygen zone, rather than of the lake surface temperature as has been suggested previously. Our analyses provide a thorough accounting of spatiotemporal variation in warming rates, offering strong evidence that thermal and ecological shifts observed in this massive tropical lake over the last century are robust and in step with global climate change., PLoS ONE, 10 (7), ISSN:1932-6203