Browsing by Author "Mgana, H. F."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Diel vertical distribution and life history characteristics of Tropodiaptomus simplex and its importance in the diet of Stolothrissa tanganicae, Kigoma, Tanzania.
    (2014) Mgana, H. F.; Herzig, Alois; Mgaya, Yunus D.
    Tropocyclops simplex abundance, diel distribution and the impact of the planktivore fish Stolothrissa tanganicae on the T. simplex population were studied at a deep-water site in Kigoma Bay, Lake Tanganyika during the wet period (October 2008–February 2009). The top 40 m were examined using discrete depth samples, filtered through a 40-μm mesh. Ovigerous and copepodids of Tropodiaptomus simplex exhibited a very clear diel vertical migration. Ovigerous females of Tropodiaptomus were negligibly low in the 0–30 m depth during the day, while at night they stayed above 20 m. Tropodiaptomus nauplii did not show any clear diel vertical migration. The contribution of adults, copepodite and nauplii stages to the total numbers of Tropodiaptomus simplex was 8.2, 8.6 and 83.2%, respectively. Stolothrissa tanganicae stomachs were analysed to quantify the contribution of zooplankton in their diets, which revealed a dominance of Tropodiaptomus females and the electivity indices proved that T. simplex females (with or without eggs) were highly selected by S. tanganicae, which could probably be explained by size-selective feeding. Life table analysis indicated that approximately 60% of T. simplex nauplii did not develop into copepodites, a loss which could not be explained by the results of the present study. 68% of the fish gut contents were contributed by female Tropodiaptomus individuals and the contribution of shrimps and Cyclopidae increased substantially to almost 20%. S. tanganicae consumed largely ovigerous Tropodiaptomus females. However, eggs found in the guts were significantly smaller than those found in the zooplankton discrete samples, suggesting that digestion had started. The calculated electivity indices underline that ovigerous and non ovigerous females of T. simplex are being positively selected in the feeding process. It infers existence of selective predation in L. Tanganyika by S. tanganicae on females of T. simplex (with or without eggs) and as a result distinct vertical migration as a predation escape mechanism is performed.
  • Thumbnail Image
    Item
    Supplemental Effects of Mixed Ingredients and Rice Bran on the Growth Performance, Survival and Yield of Nile Tilapia, Oreochromis Niloticus Reared in Fertilized Earthen Ponds
    (Springer, 2016) Samwel Mchele Limbu; Shoko, Amon P.; Lamtane, Hieromin A.; Kishe‑Machumu, M. A.; Joram, M. C.; Mbonde, A. S.; Mgana, H. F.; Mgaya, Yunus D.
    Unaffordability of commercial feeds to semi‑intensive Nile tilapia, Oreochromis niloticus farmers has led to reliance on supplemental feeding and fertilization for nutrition of their fish without a scientific basis. This study compared the growth, survival, condition factor and yield performance of O. niloticus fed on mixed ingredients (MI) and rice bran alone (RB) diets reared in fertilized earthen ponds in small scale farmers’ ponds. The study also determined phytoplankton composition, biomass and abundance in the experimental ponds. Quadruplicate ponds were stocked with O. niloticus and African sharptooth catfish, Clarias gariepinus at a stocking ratio of 1:3. The initial mean weights of O. niloticus and C. gariepinus were 14.62 ± 0.61 and 20.34 ± 1.44 g respectively. The fish were fed on MI and RB diets with protein content of 184.74 and 126.06 g kg−1 respectively for 270 days. The results showed that growth performance, survival rate and condition factor of O. niloticus were not affected by either feeding with MI or RB diet (p > 0.05). Moreover, there were no significant differences obtained in phyto‑plankton biomass and abundance in O. niloticus ponds fed on the two diets (p > 0.05). Furthermore, feeding O. niloticus either on MI or RB diet did not affect the net and gross fish yields (p > 0.05). The study revealed that the use of either MI or RB diet does not significantly affect the performance of O. niloticus cultured in semi‑intensive earthen ponds where natural food organisms are an integral part of the culture system. Rice bran could be used for semi‑intensive culture of O. niloticus in fertilized ponds to boost the production based on its availability and low cost.