One of the biggest problems the world is currently experiencing is the rapid rise of antimicrobial resistance, especially in developing nations. This cross-sectional study determined the antimicrobial susceptibility pattern of Escherichia coli, Klebsiella pneumoniae, and other Gram-negative bacteria isolated from farmed fish, manures, pond water, and fish feed in Dar es Salaam, Tanzania. 210 isolates belonging to 17 bacteria species, most predominantly K. pneumoniae (38.6%), followed by E. coli (17.1%) were recovered. Overall, the highest resistance was against ampicillin (80.5%), cefoxitin (29.5%), doxycycline (21.4%), and sulfamethoxazole-trimethoprim (15.2%). Of the 210 isolates, 68 (32.38%) were multidrug-resistant (MDR), with some isolates being resistant to 5 or more different classes of antibiotics, including cefoxitin, cefotaxime and ceftazidime (cephalosporins), imipenem, and meropenem (carbapenems), tetracyclines, ciprofloxacin (quinolones) and sulfamethoxazole (sulphonamide). The most frequent MDR patterns for E. coli were ampicillin-doxycycline-sulfamethoxazole-trimethoprim and ampilicilin-ciprofloxacin-doxycycline-sulfamethoxazole-trimethoprim, each was observed in 18.8% of the isolates. The highest proportion of MDR bacteria was found in manure (64.3%), followed by water (31.0%), fish (30.2%), and feeds (20.0%). The abundance of resistant bacteria in the aquaculture environment is concerning since they can be transferred across human-animal-environmental compartments, thereby affecting the whole ecosystem.