Browsing by Author "Yunus D., Mgaya"

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    Effect of stocking density on growth performance, survival, production and economic benefits of African sharptooth catfish (Clarias gariepinus) monoculture in earthen ponds.
    (Springer, 2016-08-02) Amon P., Shoko; Samwel Mchele Limbu; Yunus D., Mgaya
    The present on-farm study assessed the effect of different stocking densities on growth, production, and financial benefits of African sharptooth catfish (Clarias gariepinus) in earthen ponds for 180 days. Low stocking density (LSD), medium stocking density (MSD), and high stocking density (HSD) of 3, 6, and 9 fish m−2, respectively, were tested. C. gariepinus stocked at LSD and MSD showed significantly higher weight gain, specific growth rate, and final mean weight than those cultured at HSD (P < .05). There was a significant linear relationship between the stocking density and the yields and financial variables (P < .05). Net fish yields were significantly higher for C. gariepinus reared at HSD and MSD than those stocked at LSD (P < .05). Similarly, C. gariepinus raised at MSD and HSD generated significantly more profit than those cultured at LSD (P < .05). Results demonstrated that farmers can achieve high net yield and financial benefits by stocking C. gariepinus at HSD of 9 fish m−2.
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    Phytoplankton and food selectivity in Nile tilapia reared in earthen ponds under monoculture and polyculture with African Sharptooth catfish.
    (Multidisciplinary Digital Publishing Institute (MDPI), 2017-06-16) Athanasio S., Mbonde; Samwel Mchele Limbu; Amon P., Shoko; Yunus D., Mgaya
    Phytoplankton availability is one of the most important biotic factors affecting the successful culture of Nile tilapia (Oreochromis niloticus, Linnaeus) in semi-intensive ponds. The present study investigated phytoplankton composition, abundance and food selectivity in Nile tilapia Oreochromis niloticus (Linnaeus, 1758) reared in monoculture and polyculture system with African sharptooth catfish Clarias gariepinus (Burchell 1822) in earthen ponds. Water samples and stomachs of 144 O. niloticus were collected from respective pond systems for examination of phytoplankton composition and abundance. The obtained phytoplankton species in water and stomachs were used to determine food selectivity of O. niloticus. The results showed significantly higher Chlorophyceae in polyculture than monoculture ponds. The gut contents of O. niloticus from both systems were mainly composed of Bacillariophyceae, Euglenophyceae and Cyanophyceae and detritus and insect remains. Bacillariophyceae, detritus and insect remains were selected as food by O. niloticus cultured in both systems. Findings from this study show that, under monoculture and polyculture pond systems, O. niloticus exhibit selective feeding consuming more Bacillariophyceae, detritus and insect remains.The results suggest that fish farmers can practice either monoculture or polyculture of O. niloticus without affecting its food selectivity.
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    Temporal patterns in phytoplankton, zooplankton and fish composition, abundance and biomass at Shirati Bay, Lake Victoria, Tanzania.
    (Wiley, 2017-03-22) Revania K., Waya; Samwel Mchele Limbu; Godfrey W., Ngupula; Chacha, Mwita; Yunus D., Mgaya
    Shirati Bay is among the important breeding and nursery sites for major fish species in Lake Victoria. Weekly samplings were conducted to assess the temporal patterns in phytoplankton, zooplankton and fish composition, abundance and biomass in relation to prevailing water quality parameters. The study also determined the influences of plankton dynamics and water quality on the fish catch composition and biomass. It was hypothesized that temporal patterns in the composition, abundance and biomass in the plankton in the bay are controlled by water quality parameters that, in turn, affect the composition and biomass of fish catches. The phytoplankton comprised mainly cyanophytes and bacillariophytes, while the zooplankton were dominated by copepods. The heavy rain season exhibited a significantly higher plankton abundance and biomass than the dry season. The plankton abundances in both seasons exhibited significant positive correlations with water temperature and transparency. The phytoplankton community was controlled by calanoid and cyclopoid species. At higher trophic levels, Lates niloticus juveniles, Oreochromis niloticus juveniles and haplochromines controlled Cladocera and Cyclopoid copepods, while Tilapia rendalli juveniles controlled the Rotifera. This study revealed that Cyanophyta and Bacillariophyta are the dominant phytoplankton, whereas cyclopoids dominate the zooplankton species in the bay. These dominant plankton groups are partly controlled by rainfall, water temperature and transparency. Fish biomass, zooplankton and phytoplankton exhibit a typical predator–prey inverse relationship. Thus, evaluation of the plankton composition, abundance and biomass should be mandatory during fisheries stock assessments to effectively manage the fishery resources in the bay.