In recent years, microbial fish safety is getting a close attention from regulatory agencies and consumers. Therefore, fish farm raising rainbow trout and affiliated slaughterhouse and smoking plants were evaluated for the occurrence of Listeria monocytogenes. Samples including raw fish, swabbings of equipment or other surfaces, as well as processing water, salt, fish feed and fish samples taken after various stages of processing were collected from thirty different locations in the plant. For the detection of L. monocytogenes, both conventional and Listeria Rapid Test (LRT) were used. L. monocytogenes was detected in thirty out of sixty samples (50%) by LRT, while it was detected in thirty-four out of sixty samples (57%) by conventional method. No L. monocytogenes was detected from raw fish, smoked fish (before handling) and processing water, but it was detected in all environmental samples including swabbings of equipment or other surfaces and smoked fish samples after filleting.