Browsing by Author "Munubi, Renalda N."
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Item Assessment of body size and catch per unit effort of Nile perch (Lates Niloticus) caught using different fishing gears at Magu district in Lake Victoria, Tanzania(African Journal of Biological Sciences, 2020) Munubi, Renalda N.; Nyakibinda, Julitha N.Effort (CPUE) of Nile perch (Lates cf. niloticus) captured using three common fishing gears at Magu district in Tanzania. Three landing sites along Lake Victoria were selected for this assessment. Each site was visited twice per week for two months. At each site 10 boats were identified based on the gear used and randomly selected for fish count. Ten fish per boat were taken for weight and length measurements. The results show that the main fishing gears used to catch fish at all sites were gillnet (GN), long line (LL) and beach seine (BS). Mean length of captured fish recorded from each gear were 33.7, 41.5 and 43.8 for beach seine, gillnets and long lines respectively, which was below the minimal required length of 50 cm. Large proportion of small landed fish were observed in vessels fishing with beach seine, this was due to illegal nature of the beach seine, where by fishermen used small mesh sizes of 10 mm to 12 mm. However, beach seine had higher CPUE (kg/gear/day) (44.9) and gillnet had the lowest (22.6). This study revealed that the mean length from all sites were below the legal minimum size required by the Tanzanian government, suggesting that all beaches are involves in over exploration of fish.Item Do grazers respond to or control food quality? Cross-scale analysis of algivorous fish in littoral Lake Tanganyika(Springer-Verlag GmbH Germany, 2018) Munubi, Renalda N.; Mclntyre, Peter B.; Vadeboncoeur, YvonneFood quality determines the growth rate of primary consumers and ecosystem trophic efficiencies, but it is not clear whether variation in primary consumer densities control, or is controlled by, variation in food quality. We quantified variation in the density and condition of an abundant algae-eating cichlid, Tropheus brichardi, with respect to the quality and productivity of algal biofilms within and across rocky coastal sites in Lake Tanganyika, East Africa. Adjacent land use and sediment deposi- tion in the littoral zone varied widely among sites. Tropheus brichardi maximized both caloric and phosphorus intake at the local scale by aggregating in shallow habitats: algivore density decreased with depth, tracking attached algae productivity (rETR MAX ) remarkably well (r 2 = 0.84, P = 0.00033). In contrast, algivore density was unrelated to among-site variation in algal productivity. Rather, there was significant increase in algal quality (r 2 = 0.44, P = 0.011) and decrease in algal biomass (r 2 = 0.53, P = 0.0068) with T. brichardi density across sites, consistent with strong top-down control of primary producers. The amount of inorganic sediment on rock surfaces was the strongest predictor of among-site variation in algivore density (r 2 = 0.69, P = 0.00096), and algivore gut length increased with sedimentation (r 2 = 0.36, P = 0.034). These patterns indicate extrinsic and top-down forcing of algal food quality and quantity across coastal landscapes, combined with adaptive habitat selection by fish at the local scale. Factors that degrade food quality by decreasing algal nutrient content or diluting the resource with indigestible material are likely to depress grazer densities, potentially dampening top-down control in high- light, low-nutrient aquatic ecosystems.Item Effect of water velocity on ammonium and nitrite removal in pilot scale fixed bed biofilters(ELSERVIER, 2021-03) Arvind, Erik; Munubi, Renalda N.; Chenyambugaa, Sebastian WThe effect of water velocity on nitrification rates in fixed bed biofilters was investigated in three freshwater pilot scale RAS with rainbow trout. Removal of total ammonia nitrogen (TAN) and nitrite-nitrogen were assessed by NH4Cl spikes and tested at four different water velocities in the biofilters (1.4, 5.4, 10.8 and 16.2 m h− 1) under identical conditions. Water velocities below 10.8 m h− 1 significantly reduced TAN- and nitrite removal rates. The surface specific TAN removal rates correlated with the TAN concentrations at the water velocities 10.8 and 16.2 m h− 1, and the first order surface removal rate constant was estimated at 0.45 m h− 1. However, no correlations between TAN removal and TAN concentrations were found at the lowest velocities. Up to five-fold elevated nitrite levels were found in the RAS when biofilters were operated at 1.4 m h− 1 compared to the trials at other water velocities, substantiating the significant effect of water velocity on both nitrification processes. The importance of biofilter hydraulics documented in this pilot scale RAS probably have implications for design and operation in larger scale RAS.Item Effects of Climate Change and Anthropogenic Activities on Algivorous Cichlid Fish in Lake Tanganyika(IGI Global, 2021) Munubi, Renalda N.; Lamtane, Hieromin A.Over the last century, water temperatures in Lake Tanganyika have risen due to climate change, which increased thermal stratification and reduced the magnitude of nutrient availability. A rise in temperature increases the C:N:P ratio resulting in a poor algal diet. In addition, lake littoral habitat is experiencing increased sediment load due to deforestation of the watershed caused by anthropogenic activities. Sediments cover benthic algae and reduce its nutritional value, consequently affecting the foraging behavior, distribution, and growth performance of algivorous fish. Algae and algivorous fish are an important link in the lake food chain; therefore, if the rise in temperature will continue as predicted, then this may have a cascading effect for the rest of the community in the food chain including human being. This, in turn, may contribute to food insecurity at local and regional levels. To counteract this adaptation and mitigation measures such as environmental monitoring systems and creating new opportunities should be considered.Item Effects of fertilization and concentrate feeding on water quality and growth performance of Nile tilapia (Oreochromis niloticus) grown in concrete tanks(African Journal of Biological Sciences [Associate Organisation], 2020-10) Chenyambuga, Sebastian W; Munubi, Renalda N.; Madalla, Nazael A.; Quagrainie, Kwamena; Frimpong, Emmanuel; Egna, HillaryAn experiment was conducted to compare the effects of fertilizer application alone, concentrate feeding alone and combination of fertilization and feeding on water quality parameters and growth performance of sex-reversed Nile tilapia (Oreochromis niloticus). Three treatments (weekly fertilization with urea and DiAmmonium Phosphate (DAP), concentrate feeding at 5% of fish body weight and weekly fertilization with urea and DAP plus concentrate feeding at 2.5% of fish body weight) were randomly allotted to nine concrete tanks. Three fingerlings per m2 were stocked in the tanks and grown for 166 days. Results indicated that treatment had significant effect (p 0.001) on water Dissolved Oxygen (DO), conductivity, total dissolved solids, nitrate and phosphorus but not on pH, salinity, temperature, ammonia and alkalinity. Fish cultured under the combination of feeding and fertilization had higher (p 0.0001) weight gain (257.37 ± 5.71 g), growth rate (1.50 ± 0.04 g/day), yield (13,128.35 kg/ha/year) and lower Feed Conversion Ratio (FCR) (1.89 ± 0.03) than those reared under feeding alone and fertilization alone. It is concluded that the combination of weekly fertilization and concentrate feeding at 2.5% of fish body weight is better than either weekly fertilization alone or feeding alone at 5% of fish body weight.