Browsing by Author "Mwandya, Augustine W."
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Item Biological connectivity and nursery function of shallow-water habitats in Chwaka Bay(2012) Gullström, Martin; Dorenbosch, Martijn; Lugendo, Blandina; Mwandya, Augustine W.; Mgaya, Yunus D.; Berkström, CharlotteItem Comparative Performance of Mixed-Sex and Hormonal-Sex-Reversed Nile Tilapia Oreochromis Niloticus and Hybrids (Oreochromis Niloticus × Oreochromis Urolepis Hornorum) Cultured in Concrete Tanks(Springer Link, 2016) Mbiru, Moses; Samwel Mchele Limbu; Chenyambuga, Sebastian W.; Lamtane, Hieromin A.; Tamatamah, Rashid; Madalla, Nazael A.; Mwandya, Augustine W.Uncontrolled breeding and precocious maturity in Nile tilapia, Oreochromis niloticus can be avoided by using all-male population. This study compared the growth performance, survival rate, condition factor and final fish tank biomass (yield) of mixed-sex and hormonal-sex-reversed O. niloticus and hybrids (O. niloticus × O. urolepis hornorum) cultured in tanks. Sex-reversed males were produced by feeding newly hatched fry with a diet containing 60 mg of 17α-methyltestosterone for 28 days. Fourteen O. niloticus with initial mean weight (±standard error) of 0.50 ± 0.04, 0.48 ± 0.06 and 0.46 ± 0.01 g for mixed-sex, sex-reversed and hybrids, respectively, were separately stocked in triplicate tanks at a density of two fish m−2 and fed a 300 g kg−1 crude protein diet for 12 weeks. Results showed that hybrids had significantly higher final mean weight (31.41 ± 0.33 g) than hormonal-sex-reversed (25.82 ± 1.51 g) and mixed-sex O. niloticus (19.50 ± 1.26 g; p < 0.05). Similarly, sex-reversed O. niloticus had significantly higher final mean weight than mixed-sex (p < 0.05). The condition factor of hybrids (1.71 ± 0.05) was significantly higher than that of sex-reversed (1.46 ± 0.01; p = 0.001) and mixed-sex O. niloticus (1.43 ± 0.01; p = 0.001). Survival rate was not significantly different among treatments (p = 0.445). The final fish tank biomass was significantly higher in hybrids (535.24 ± 31.67 g tank−1) and hormonal-sex-reversed (486.52 ± 33.70 g tank−1) than mixed-sex O. niloticus (330.05 ± 17.08 g tank−1; p < 0.05). This study demonstrates that hybrids have superior growth performance and condition factor than sex-reversed and mixed-sex but have similar yields to hormonal-sex-reversed O. niloticus. These results suggest that O. niloticus farmers can improve growth rate and yield by rearing hybrids without affecting survival rate.Item Distribution patterns of the striped mullet (Mugil cephalus) in mangrove creeks of Zanzibar, Tanzania. African Journal of Marine Science(2010) Gullström, Martin; I, Bryceson; Öhman, Marcus C; Mgaya, Yunus D.; Mwandya, Augustine W.Spatial and seasonal variations in density of striped mullet Mugil cephalus were investigated in four mangrove creeks in Zanzibar, Tanzania, during a one-year cycle. Fish were collected monthly in the lower, intermediate and upper reaches of each creek using a beach-seine net. All fish collected were juveniles between 2 and 16 cm standard length. The density of juvenile mullet differed significantly among the creeks, but the spatial patterns within them were consistent with higher densities upstream in three of the creeks. Generally, small mullet (2–10 cm) were more abundant in the upper reaches compared to the lower and intermediate reaches. Seasonal patterns were weak, although mullet densities were high during the period of heavy rains (March–May). Principal component analysis showed that a muddy substrate with microphytobenthos was positively correlated with high mullet densities, although site-specific variables such as shallow water depth and water clarity were also significantly correlated. Our findings suggest that the densities of juvenile striped mullet vary among sites and creeks in response to refuge availability from turbid, shallow water and the accessibility of food from benthic microalgae.Item Effects of Elevated Carbon Dioxide and Temperature on Survival and Morphology of Japanese Whiting Sillago Japonica(2016) Yona, G.; Madalla, Nazael; Mwandya, Augustine W.; Ishimatsu, A.; Bwathondi, Philip O. J.The objective of the present study was to examine the effect of elevated CO2 and temperature on survival and morphology of Sillago japonica yolk sac larvae under the Institute for East China Sea Research (ECSER) Nagasaki, Japan. In this study, we examined hatching success, survival and morphology of the larvae of Sillago japonica under four conditions: control (C), seawater pCO2 382µatm, temperature 27 °C; high CO2 (HC), 915µatm, 27 °C; high temperature (HT), 385 µatm, 31 o C; and high CO2+high temperature (HCT), 932µatm, 31 o C. Fertilized eggs were obtained from broodstock reared in natural seawater, and transferred to experimental containers in each treatment. Hatched larvae were observed until the completion of yolk sac absorptions on 3 days post hatching (dph). The experiment was repeated four times with 4 replicates for each treatment in each experiment. Also, the temperature appeared to have exerted a stronger influence on hatching success (Hs) and larval survival (Sv): Hs and Sv at 3 dph were both significantly (p>0.05) depressed in HT (Hs 52.5±1.25%, Sv 23.8±4.38%) and HCT (Hs 51.3±3.13%, Sv 20.0±0.63%) treatments than in C (Hs 98.1±0.94%, Sv 74.4±2.03%) and HC (Hs 95.0±2.5%, Sv 49.7±3.44%) treatments. In contrast, CO2 was the predominant factor responsible for morphological abnormality: percentage morphological abnormality was significantly (p>0.05) higher in HC (15.8±2.72%) and HCT (41.0±10.86%) treatments than in C (0.4±0.65%) and HT (2.4±2.40%) treatments. Most individuals in HC and HCT treatments had body axis either curved or bent, with aberrant swimming behavior. These results indicate that projected future ocean environments will have significant negative impacts on hatching success, and larval survival and morphology of S. japonica, which might have serious ramifications for recruitment of the species. Comparative studies on other teleost and elasmobranch species are critically needed.Item Fish assemblages in Tanzanian mangrove creek systems influenced by solar salt farm constructions.(2009) Mwandya, Augustine W.; Gullström, Martin; Anderson, Mathias H; Mgaya, Yunus D.Deforestation of mangrove forests is common occurrence worldwide. We examined fish assemblage composition in three mangrove creek systems in Tanzania (East Africa), including two creeks where the upper parts were partly clear-cut of mangrove forest due to the construction of solar salt farms, and one creek with undisturbed mangrove forest. Fish were caught monthly for one year using a seine net (each haul covering 170 m2) within three locations in each creek, i.e. at the upper, intermediate and lower reaches. Density, biomass and species number of fish were lower in the upper deforested sites compared to the mangrove-fringed sites at the intermediate and lower parts in the two creeks affected by deforestation, whereas there were no differences among the three sites in the undisturbed mangrove creek system. In addition, multivariate analyses showed that the structure of fish assemblages varied between forested and clear-cut sites within the two disturbed creeks, but not within the undisturbed creek. Across the season, we found no significant differences except for a tendency of a minor increase in fish densities during the rainy season. At least 75% of the fishes were juveniles and of commercial interest for coastal fisheries and/or aquaculture. Mugil cephalus, Gerres oyena and Chanos chanos were the most abundant species in the forested sites. The dominant species in the clear-cut areas were M. cephalus and Elops machnata, which were both found in relatively low abundances compared to the undisturbed areas. The conversion of mangrove forests into solar salt farms not only altered fish assemblage composition, but also water and sediment conditions. In comparison with undisturbed areas, the clear-cut sites showed higher salinity, water temperature as well as organic matter and chlorophyll a in the sediments. Our results suggest that mangrove habitat loss and changes in environmental conditions caused by salt farm developments will decrease fish densities, biomass and species numbers as well as alter the overall fish assemblage composition in the salt farm area but not downstream in the creek.Item Macroalgae as Biofilters of Dissolved Inorganic Nutrients in an Integrated Mariculture Tank System in Zanzibar(2001) Mwandya, Augustine W.; Mtolera, Matern S. P.; Pratap, Harish B.; Jiddawi, Narriman S.A laboratory experiment was conducted to determine the capacity of themacroalgae Eucheuma denticulatum, Gracilaria crassa and Ulva reticulatato remove dissolved inorganic nutrients from finfish effluents in seriallyarranged tank systems. The aim was to determine the capacity ofmacroalgae which could be used in an integrated maricultre pond systemat Makoba, Zanzibar. Seawater from the reservoir entered the finfish tanksfirst, then drained through plastic pipes into the shellfish units and finallyinto the macroalgae units before being discharged back into the sea. Thewater residence time in each tank was 4 days. The performance of each ofthe different units was assessed in terms of total ammonia-N, phosphate-P and nitrate-N produced by finfish, and then, the removal of these nutrientsby shellfish and macroalgae biofilters. The levels of dissolved inorganicnutrients were highest in the finfish units and lowest in the macroalgaeunits. Increase in stocking density of macroalgae from 1g/l to 2g/l wasrelated to their increase in daily growth rates, specific growth rates andinorganic nutrient uptake rates. However optimum stocking densities werenot reached. Of the three inorganic nutrients, ammonia-N and phosphate-P was taken up by the macroalgae much more than nitrate-N. Ammonia-N removal efficiency in the system reached a maximum of about 63% at2g/l of Ulva reticulata whereas, phosphate-P and nitrate-N maximumremoval capacity were 58 and 54% respectively. Among the three species ofmacroalgae, Ulva reticulata seems to be the most efficient biofilter. It isconcluded that locally available macroalgae are good bioregulators of waterquality, thus can be applied in small scale mariculture activities and canalso generate income.Item Spatial and seasonal variations of fish assemblages in mangrove creek systems in Zanzibar (Tanzania). Estuarine, Coastal and Shelf Science(2010) Mgaya, Yunus D.; Öhman, Marcus C; Andersson, Mathias H.; Gullström, Martin; Mwandya, Augustine W.; Bryceson, IanSpatial and seasonal variations of fish assemblage composition were studied in three non-estuarine mangrove creeks of Zanzibar (Tanzania). Fish were collected monthly for one year at three sites (lower, intermediate and upper reaches) in each creek using a seine net (each haul covering 170 m2). Density, species number and diversity of fish were all higher at sites with dense cover of macrophytes (seagrass and macroalgae) than over unvegetated sandy sites. In general, fish assemblages mainly comprised juveniles of a few abundant taxa, e.g. Mugil cephalus, Mugilidae spp. and Leiognathus equulus at sites with mud substratum and Gerres oyena, Lethrinus harak and Sillago sihama at sites dominated by macrophytes. Multivariate analyses revealed significant separations in fish assemblage composition within the two creeks where the bottom substratum differed among sites. Overall, season seemed to have little effect on density, species number, diversity index (H′) and assemblage structure of fish. Water condition variables were also relatively stable across the season, although a short-term fluctuation primarily induced by decreased salinity, occurred during the heavy rains in April and May. Fish assemblage structure was not significantly affected by any of the abiotic factors tested. However, significant regressions were found between the other fish variables and environmental variables, but since these associations were mostly species-specific and generally inconsistent, we suggest that the overall distribution patterns of fish were mainly an effect of particular substrate preferences of fish species rather than contemporary water conditions.