Aquaculture is the world’s rapidly expanding and economically important food enterprise and is predicted to provide the most consistent supply of high biologic value protein in future. Due consideration is required for the improvement of certain issues related to fish nutrition for sustainable aquaculture development and optimization of the nutrition for the efficient raising of fish can warrant sustainable supply of protein to the rapidly growing population. There is a dire need to achieve a balance between proficient and safe food production with environmental sustainability in order to overcome the challenge faced by the industry. Due to environmental degradation of natural aquatic environment, semi intensive aquaculture with supplementary feeding has become predominant. Feed is usually believed as a main limitation to the development of aquaculture representing up to 60% of the total expenditure and highest recurring cost. Formulation of suitable high quality and cost effective feed from locally available and economically valuable feed ingredients is a prerequisite for the provision of quality fish fingerling that can withstand the environmental disturbances for maximum yield throughout the fish growth period. Thus the use of artificial diets to culture carps under intensive conditions particularly rohu has become inevitable in recent years to enhance aquaculture production in Pakistan. Fish meal being an essential and costly ingredient in conventional feeds formulations for fish and other animals possess various stresses for economizing the development of aquaculture including incurring costs, especially for areas far off from sea sides. The limited supplies and rising cost of fish meal have led workers to explore alternative acceptable sources of protein that can substitute fish meal and decrease its use in diets of fish to meet the demands of growing aquaculture production. Several protein sources derived from plants, animals or microbes have been worked out to serve as alternatives of fish meal without affecting fish growth. The protein obtained from bacteria, yeasts, moulds, blue green algae etc. is called as single cell protein (SCP) and is more beneficial than animal and plant proteins due to greater protein content, its production throughout the year, broad amino acid range, low fat content and eco-friendly and it can be employed in recycling of agri wastes thereby reducing pollution. Yeast has been reported by many workers to substitute fish meal in feed formulations of fish with a growth promoting and immunity development effect on fish. Yeast is a cheaper non-pathogenic fungi having large cell size and greater easily digestible protein content as compared to bacteria and can accomplish provision of protein source with balanced essential amino acids profile along with other growth promoting molecules such as vitamins for fish feed. Keeping in view the significance of cost-effective aqua feeds, the present study was aimed to cultivate yeast by employing abundantly available food wastes such as apple, mango, water melon and sugarcane bagasse followed by its identification and use and as a replacement of fish meal in feed formulations singly as lysed cell biomass as well as non lysed cell biomass with the remnants of substrate. Amongst the several agri wastes tried, higher growth of yeast was supported by 2% aqueous extract of water melon peels (WM). In this study, the optical density (1.22±0.03) was recorded after 72 hours. The growth at the last incubation period in WM was 111% higher than the mango peels, for instance. The yeast expressed highest growth at pH 7.0, 37 ᴼC and 15% inoculum size. The yeast grew best under non aerating conditions as compared to aerated conditions with corresponding cells optical density of (2.41±0.25) at 48 hours of incubation. The 2% substrate concentration was also found optimum as evidenced with optical density (3.49±0.05). Best growth of the cells under non aerating conditions is another plus point for the economical microbial cultivation at large scale wherein efforts to provide aeration cannot be accomplished without input of cost. Following cultivation under optimum conditions upto 48 hours, the wet cell biomass of the yeast was 25.6g/litre that corresponded to 6g/litre of dry biomass. Proximate analysis revealed carbohydrate, crude protein and fat upto 40.31, 33.44 and 5.08% respectively. In case of 4% powdered substrate medium the highest growth in terms of number of cells/ml (150±8.56) was obtained at pH 7.0, temperature 37 ᴼC and 15% inoculum size under non aerated conditions. When the yeast was cultured in 4% WM peels suspended medium under non aerated conditions, the dried yeast plus substrate remnants was found to contain carbohydrate, crude fiber, fat, crude protein, ash and moisture contents upto 46.56±0.09, 14.7±0.70, 1.34±0.02, 18.3±0.26, 4.00±0.06% respectively.Water quality parameters recorded on daily basis as well as physicochemical parameters after every ten days interval of control and experimental aquaria were found within the permissible limits. The room temperature was maintained between 24-30ᴼC. A 40 days’ trial was conducted to evaluate the growth profile corresponding to yeast incorporated fish diets along with control and growth was recorded after every ten days interval. At the termination of the trial (40 days) T75 showed maximum weight gain (1.38±0.100) and showed significantly increased trend from rest of the treatments T0 (0.77±0.043) (P0.001), T25 (0.90±0.022) (P<0.01), T50 (0.94±0.058) (P<0.01), T100 (0.82±0.048) (P<0.01) and TYW (0.93±0.100) (P<0.01). The corresponding percentages were 79.22, 53.33, 46.80, 68.29 and 48.38% respectively. After 20 days T75 showed significant (P<0.05) increase in feed conversion ratio as compared to control (T0) .Similar trend was also noticed for 30 days. At the termination of the trial (40 days), significantly improved feed conversion ratio was recorded for T75 in contrast to rest of the treatments T0 (P<0.01), T25 (P<0.05) and T100 (P<0.05) except T50 and TYW. T75 also showed highest feed conversion efficiency after 10 days and the value was (52.51±3.1) %. The difference was significant as compared with T0 (P <0.05), T50 (P < 0.05) and T100 (P<0.01) as shown in table 4.24 and Fig 4.24. After 20 days, T75 could express significant (P<0.05) increase over T0 only. At termination of the trial (40 days), T75 (86.82±7.3) showed significant (P<0.01 to P<0.05) increase in feed conversion efficiency from rest of the treatments In case of TYW, significantly (P<0.05) increasing trend in feed conversion efficiency (%) was recorded after 40 days as compared to 10 and 20 days. After 30 days, the average weight of T50 (P<0.05) andT75 (P<0.01) fingerlings increased significantly from T0 and the differences were 18.84 % and 30.43%, respectively. At end of the experiment T75 (2.37±0.084) showed significant (P<0.01) increase in average weight from T50 (1.97±0.063), TYW (1.95±0.103), T25 (1.94±0.007), T100 (1.81±0.052) and T0 (1.79±0.055) with corresponding percentages of 20.30, 21.53, 22.16, 30.93 and 32.40. Significant (P<0.001) increase in average weight for T25 (1.94±0.007) 86.53% was observed after 40 days as compared to zero day. Similarly T50 also showed maximum increase in average weight (1.97±0.063) 93.13% at termination of the trial. Significantly increasing trend in average weight was noticed after 20, 30 (P<0.01) and 40 (P<0.001) days and T50 showed maximum increase in average weight at termination of the trial (1.97 ±0.063). In case of TYW, significantly (P<0.001) higher average weight was observed after 30 and 40 days with values (1.4±0.020) 37.25% and (1.95 ±0.103) 91.17% as compared with zero day (1.02±0.010), respectively. No considerable increase in daily wet body weight gain (g) was observed among all the treatments upto 10 days except T75 which increased significantly from T0 (0.01±0.001) (P<0.05), T50 (0.01±0.001) (P<0.05) and T100 (0.01±0.001)(P<0.01) except T25 (0.01±0.002) and TYW (0.01±0.002). ). After 20 days T75 showed significant increase (P<0.05) in daily wet body weight gain of (0.02 ±.001) as compared to T0 (0.01 0.002) (P<0.05), T50 (0.01 0.001) (P<0.05) and T100 (0.01 0.001) (P<0.01) in a similar manner as that was recorded for 10 days. After 30 days, T75 showed significant increase in daily wet body weight gain from rest of the treatments, except T50 (0.02 ±0.001).T75 also showed significantly increasing trend (P<0.001) in daily gain of wet body weight (0.03 0.001) from T0 (0.01 ±0.003).At the termination of trial T75 (0.03±0.002) showed maximum gain in daily wet body weight that was significantly (P<0.01 to P<0.05) higher from all the other treatments. T75 showed significantly increased (P<0.01 to 0.05) relative body weight gain from T0, T50 and T100 treatments up to 10 days. After 20 days T75 (39.95± 8.62) showed maximum gain in relative body weight that was significant (P<0.05) as compared with T0 (14.78±2.38) which further increased significantly (P<0.01 to 0.05) after 30 days from rest of the treatments except T50 (59.73±2.88). At the termination of trial (40 days), T75 showed maximum gain in relative body weight (140.20±12.16) that showed significant increase from the rest of the treatments as well as control treatmentT0 (76.24±4.29). In TYW relative weight gain rate increased significantly after 30 days (P<0.05) and 40(P<0.001) days as compared with 10 days in a similar manner as that was recorded in T0 .Relative weight gain rate also showed a significantly (P<0.001) increasing trend between 20 and 40 days. Maximum gain in relative body weight was recorded as 91.09±.9.63 at the termination of trial (40 days). As regards average total length (cm) no significant increase in average total length was recorded up to 10 days among all the treatments as compared with control as well as with zero days except T100 (4.91±0.041) which showed a significantly (P<0.05) increasing trend from zero day. However, the average total length increased significantly after 20, 30 and 40 days as compared with zero days. The average total length increased significantly at end of the trial (40 days) in T75 as compared with other treatments (which didn’t differ significantly from each other) and the maximum increase recorded in T75 was 6.39±0.13 cm followed by T100 (5.70±0.053) which showed a significantly increasing trend from T100 as well as from rest of the treatments (which didn’t differ significantly from each other). No significant increase in average standard length was recorded among all the treatments upto 30 days .The average standard length increased significantly (P<0.001) after 40 days in all the treatments as compared with zero day .No significant increase was recorded among all treatments except T75 wherein maximum increase was recorded in T75 (4.73±0.06) which showed significantly increasing trend as compared with T25 (4.28±0.06) and T100 (4.23±0.06). No significant increase in average total width was recorded among all the treatments up to 30 days as compared with zero day .The average total width increased significantly (P<0.01) after 40 days in all the treatments. In general no significant increase was recorded among treatments. However, T75 did express maximum increase (1.63±0.029) which was significant as compared with T25 as well as from rest of the treatments (which didn’t differ significantly from each other) except T0. The biochemical analysis of muscle tissue of control and experimental fish fingerlings revealed no significant difference among the different fish fingerling groups regarding protein content. However, the protein content showed a significantly (P<0.01) increasing trend after 30 (400.45 mg/g) days in TYW as compared with the zero day. Non-significant increase in protein content was recorded after 40 days. As regards the total fat content, a significant increase after every 10 days interval as compared with zero day was noticed. No significant increase in fat content was recorded after 20 and 30 days followed by significant (P<0.001) elevations after 40 days. The highest fat content was recorded in T100 treatment after 20 days that was significant P<0.001as compared with rest of treatments as well as zero day, except the control T0. . No significant increase in cholesterol was observed among the control T0 and experimental fish fingerlings, except T25 and T100 which showed significantly (P<0.01) higher cholesterol level as compared with T50. The cholesterol level in the muscle tissue showed a significantly (P<0.001) decreasing trend among all fish fingerlings groups as compared with zero day. The cholesterol level decreased significantly (P<0.01) in T50 after 40 days as compared with zero days. The DNA content was found significantly higher in T50 from rest of the treatments, except TYW which showed less significant results. Significant increase in total DNA of muscle tissue was recorded after 40 days in TYW. There was no marked difference noticed between the control and experimental fish fingerlings groups regarding RNA content. RNA content increased significantly after 40 days as compared with zero days. Maximum increase in RNA content was found in TYW after 30 days. As regards the moisture and ash content, no marked difference was noticed between the control and the experimental fish fingerlings groups till the termination of the trial. Cross section of 40 days old fingerlings of different experimental groups revealed differences in the histomorphology of various anatomical structures. Differences were noticeable in the form of total diameter of intestine, size and number of villi as well as in the sub mucosa and tunica serosa .Tunica mucosa of control (T0) looked less in height as compared to T25 and other tunica layers collectively sub mucosa, tunica muscularis and tunica serosa formed a layer of less thickness as compared to the situation observed in T75. It is surprising to note that for T100 very less intestinal structural development was observed. The villi were of low height. Same was case with the other gut layers. In case of the whole yeast the overall gut structure was observed to develop better than a many of the other experimental groups." xml:lang="en_US