This study has been conducted in Lake Tana Nile tilapia, Oreochromis niloticus, fishery. The length and weight of individual O. niloticus from fishery-independent data and catch as well as effort data of fishers have been used to analyses O. niloticus fishery for 2016/2017 production year. The aim of the study was to examine the extent of immature O. niloticus exploitation in the Bahir Dar Gulf of Lake Tana area, to estimate age, growth, maximum sustainable yield (MSY) and effort at maximum sustainable yield (fMSY) for the whole lake. Fish samples were collected monthly from April 2016 to March 2017 using gillnets of different mesh sizes. Samples collected during the breeding time were used to determine the length at first maturity of fish (L50%). A logistic function was fitted to estimate L50%. Catch and effort data were collected from three sites starting June 2016 to May 2017 from Reed boat and motorized boat fisheries. Catch and effort data were also collected from the chase and trap fishery from May to July 2016. The percent of catch below L50% was calculated from the two types of fisheries. The difference in the distribution of the catch per unit effort (CpUE) of O. niloticus among study sites and seasons was tested using two-way ANOVA. Otolith samples collected from June 2016 to May 2017 were placed at 97% of ethanol for three days and they were transferred into 45% glycerol for 7 days. Sagittal otolith was ground using Carborundum papers for microscopic examination. The age of the fish was determined from the total number of translucent macrozones counted in the otoliths based on knowledge of the time of translucent zone formation and breeding season of the fish. The precision of estimated age was done by average percent error (APE) and coefficient of variation (CV). The periodicity of annuli formation was validated using marginal increment analysis (MIA) and edge analysis (EA). The von Bertalanffy Growth Function (VBGF) parameters for observed and back-calculated length at age function were estimated following a non-linear curve fitting procedure. For MSY and fMSY estimation, catch and effort data were collected from four landing sites. Linearized lengthbased catch curve analysis was employed to estimate the total mortality coefficient (Z) and natural mortality was estimated with Pauly’s empirical formula. Fishing mortality (F) was calculated as Z-M. The Jones length-based cohort analysis was used to estimate the population abundance and F coefficient by length group. The outputs of length-based cohort analysis were used as input data for the Thompson and Bell yield prediction model to predict sustainable fish yield at different levels of F-array. The L50% for males (20.5 cm) was relatively higher than xv females (19.6 cm). The overall mean CpUE for O. niloticus in Lake Tana was 23.8 kg per trip. The CpUE was significantly different among the study seasons (P = 0.000) and sites (P = 0.002). Of the total catch at Bahir Gulf, about 24% of the motorized boat and reed boat fisheries and 46% of the chase and trap fishery were below L50%. Totally 1,596 samples were collected for age and growth works. The highest percentage of the translucent zone was recorded in June, July, January and February; whereas the lowest was observed in October, November, March, April, and May. The mean relative marginal increment was highest in November, December and May; and the lowest was observed in June, July, J