A dissertation for the degree of master in tropical animal production of sokoine university of agriculture. Morogoro, Tanzania.Growth performance and productivity of Nile tilapia (Oreochromis niloticus) is highly influenced by water quality in the pond. On the other hand, water quality is influenced by the climate and ecological conditions of the place. This study evaluated the growthperformance, survival rate, yield, body length-weight relationship and condition factor of Nile tilapia (Oreochromis niloticus) cultured in two districts; Mbarali and Mufindiof Mbeya and Iringa regions,respectively. Furthermore, plankton biomass yield, species composition and biochemical composition of the algae collected from the ponds located in these two districts were assessed. The two districts experience different ecological conditions withhigh and low temperatures.In each district fish were raised in four earthen ponds,each with an average size of 650 m2 for six months. There were two sites per district and two ponds in each site. All ponds were initially drained, cleaned, dried and refilled with water. The ponds were fertilized seven days prior to stocking using urea and Diammonium phosphate (DAP) at a rate of 3 g/m2 and 2 g/m2,respectively.Thereafter, fertilization was done fortnightly throughout the experimental period. Sex reversed Nile tilapia fingerlings with an average body weight of 1.00 g were stocked at a stocking density of 2 fingerlings/m2. Fish were fed with supplementary diet containing 25% crude protein (CP) at 10% of fish body weight in the first month, followed by 5% for the remaining five months. Feeding was done twice daily, at 10.00 to 10.30 am and at04.00 to 04.30 pm. Body weight, length, width and water quality parameters,namelytemperature, dissolved oxygen, transparency, conductivity, salinity, alkalinity, ammonia, nitrate and phosphorus were measured biweekly. Analysis of variance (ANOVA) was used to test the effect of location on growth performance and water quality parameters. Duncan’s New Multiple Range test was used to test the significance of the differences between a pair of treatment means. The relationships between fish growth and water quality parameters were assessed using correlation analysis while multiple regression analysis was used to assess the influence of water quality parameters on fish growth. All statistical analyses were performed using the General Linear Model (GLM) of the Statistical Analysis System software (SAS, 2000) for Windows. Significant differences were judged at a probability level of p ≤ 0.05. Results revealed that, the growth performance of sex-reversed Nile tilapia was higher (p<0.05) in Mbarali than in Mufindi district where there was high temperature and low temperature, respectively. The mean growth rate (1.26 ± 0.03 g/day), specific growth rate (3.12 ± 0.02%), mean final weight (228.68 ± 4.99 g) and estimated annual yield (6828.43 ± 407.95 kg/ha/year) obtained from the Nile tilapia (Oreochromis niloticus) cultured at Mbarali district were significantly higher than of those reared in Mufindi district (mean growth rate = 0.48 ± 0.03 g/day, specific growth rate = 2.52 ± 0.02%, mean final weight = 86.68 ± 4.79 g and estimated annual yield = 4465.29 ± 407.95 kg/ha/year). Mean final body length and width were also higher for the fishgrown in ponds located at Mbarali (body length = 21.87 ± 0.16 cm and width = 7.71 ± 0.07 cm) than of those grown at Mufindi (body length = 16.14 ± 0.15 cm and width = 5.55 ± 0.07 cm). The results further revealed that, water quality parameters (temperature, salinity, conductivityand alkalinity) were higher in ponds located at Mbarali than in those located at Mufindi district (p< 0.05) while water transparency was significantly higherin ponds located at Mufindi compared to that of those located at Mbarali. The mean temperature, dissolved oxygen (DO), pH, conductivity, salinity, transparency, phosphorusand nitrate in Mbarali were 27.72± 0.25 0C, 6.17 ± 0.27mg/L, 6.91 ± 0.15, 121.62 ±3.27 μS/cm, 57.35 ± 1.86 mg/L, 15.73 ± 0.56cm, 1.33 ± 0.17mg/L, and 7.72 mg/L, respectively. The mean temperature, dissolved oxygen (DO), pH, conductivity, salinity, transparency, phosphorusand nitrate in Mufindi were 21.93 ± 0.25 0C, 6.09 ± 0.27 mg/L, 6.96 ± 0.15, 31.81 ± 3.27 μS/cm, 13.18 ± 1.86mg/L, 17.25 ± 0.56 cm, 0.98 ± 0.17 mg/Land 7.71 ± 0.24 mg/L,respectively. Regression of water quality parameters on growth showed that DO and transparency had significant positive influence only for fish growth at Mbarali while temperature and conductivity had positive and significant influence on the growth of fish at Mufindi district. The correlation coefficients (r) between weight and length in both experimental locations were above 95%, indicating a strong relationship between live weight and body length of the fish. The regression coefficient (b) values in the length-weight relationships were 2.87 and 2.94 for Mbarali and Mufindi, respectively, indicating negative allometric growth. The mean condition factor (K) values ranged from 2.74 to 3.50 for Mbarali and 1.96 to 2.40 in Mufindi. The exponential value ‘b’ and the condition factor (K) differed significantly between the two experimental locations (p< 0.05). The analysis of plankton species composition revealed no significanctdifference in number of species found in experimental ponds located in the two locations (p> 0.05). Common species found in both locations belonged to the following classes; Bacillarophyceae, Chlorophyceae, Cynophyceae, Euglenoidea, Foraminifera, Heterotrichea, Monogononta, Tubulinea and Zygnemaphyceae.The class Eurotatoria was found only at Mufindi district. Algal samples collected from Mbarali had higher (p ≤ 0.05) biomass (51.74 ± 1.83 g DM/m2) and crude protein (CP) (16.46 ± 0.65%) contents compared to those collected from Mufindi (biomass = 39.25 ± 1.83 g DM/m2, CP = 14.44 ± 0.65%).From the results of this study it is concluded that, differences in climatic conditions between experimental locations influence significantly the production performance, length-weight relationship and condition factor of Nile tilapia. Plankton species composition, chemical compositions differ slightly between the two experimental locations.