Browsing by Author "Leonard, Levinus"

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    Assessment of some commercial finfish species in mangrove systems of Kisakasaka and Uzi, Zanzibar
    (University of Dar es Salaam, 2013) Leonard, Levinus
    Knowledge on the status of commercially important mangrove dependent finfish in Zanzibar is limited to Chwaka and Makoba Bays. Spatial variation in fish size structure, proportion, relationship between water environmental factors and fish abundance were studied at Kisakasaka and Uzi Island mangrove ecosystems, Zanzibar. The study aimed at generating information on the status of mangrove dependent commercial finfish in these relatively unstudied ecosystems. Samples were obtained with the seine net at low spring tides. Sizes were measured and length-weight regressions were established. Fish assemblage structure was determined and size structure of the most common species established. Correlations between fish species abundance and environmental parameters such as water temperature, pH, salinity and Dissolved Oxygen were investigated. Fish proportion in the catch was determined by calculating percentage composition of the target species. Analysis indicated that environmental factors had little influence on fish abundance at both Kisakasaka and Uzi sites. Size structure varied significantly between sites for all species unlike proportion which varied significantly only for Mugil cephalus species. Absence of key species, such as the milkfish Chaws chanos, which is currently being promoted as a key species for small scale aquaculture in Tanzania, could indicate that fingerling supply from the wild may be a constraint to the fast-growing aquaculture industry in future. It was concluded that commercially important finfish in mangrove systems of Zanzibar are unsustainably harvested and urgent conservation and sustainable management initiatives of these resources and their environment are required to protect them from further decline.
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    Potential for aquaculture of Nile and Rufiji tilapia hybrids
    (University of Dar es Salaam, 2019) Leonard, Levinus
    This study focused on understanding the effects of stocking density, salinity and commercial dietary probiotics on growth performance ofNile tilapiaand Rufijitilapia all-male hybrids. The study also investigated genetic diversity within and between Nileand Rufiji tilapia using ddRAD sequencing. Furthermore, the study explored differences in CP contents between parents and hybrids. Hybridization was done and 100% male hybrids were produced. The experiments were replicated three times while parents and hybrids were fed with on-site formulated diets of 40% protein inclusion. Growth indices SGR, weight gain, FCR and survival rates were measured fortnightly. In the stocking density experiments, the 10 fish/m3 stocking density showed better growth performance than 5 (control), 15 and 20 fish/m3. Salinity showed significant influence on the FCR (p < 0.05) only. The 15-25 salinity revealed higher hybrid growth. Probiotics experiments indicated similar trends in growth performance at 2, 4 and 6g/kg and control (non-probiotics treated) feed treatments. The 4 and 6 g/kg feed treatments indicated significant growth performance differences (p < 0.05) from the control diet and 2 g/kg for both L. plantarum and S. cerevisiae. Protein content varied significantly between parents and the subsequent hybrids (p < 0.05). Both the Nile and Rufiji populations were within the Hardy Weinberg Equilibrium (HWE). The inbreeding values (FIS) for each population showed that the individuals were less related. The Nile tilapia population consisted of two individuals that clustered differently from other individuals. These populations showed great genetic variability between with FST value of 0.81. These findings indicate that tilapia hybrids mariculture can be used to improve fish production. Also, probiotics and salinity improve hybrid tilapia growth. The lower protein content of hybrids is overcompensated by their higher growth rates and and survival in brackish and marine environments making them important for consideration in aquaculture development. Hybrids used in this study can be used as alternative to homonal sex-reversal in production of all-male tilapia fingerlings. The Nile and Rufiji populations studied can be used as raw material for setting up a breeding programme in Tanzania to improve aquaculture production due to their great genetic diversity.