The aim of the present study was to evaluate the relationship between histamine content and microbial load of refrigerated rainbow trout fillet during different storage times (0, 5, 10, 15 and 20 days). In order to determine the extent of reduction in quality of the fillets, spoilage indicators including total bacterial load, psychrotropic bacteria, coliforms, lactobacillus, Staphilococcoi, yeast and mold, E. coli and Salmonella were studied. The results showed that histamine content increased significantly (p<0.05) from 1.96 to 7.98 mg kg-1 during 20-day storage. The bacterial load of the plates indicated that all bacterial spoilage parameters with the exception staphilococcoi increased significantly during the 20-day refrigeration period, in which the highest rate of growth was achieved for the psychrotropic bacteria (10.23 log CFU g-1 ) and total bacterial load (11.48 log CFU g-1). All fillets were declared unfit for consumption after the fifth day of preservation according to the allowable limit defined for the total bacterial load (7 log CFU g-1). No salmonella and E. coli were observed in all samples. There was a highly significantly (p<0.01) positive correlation (0.64) between histamine content and total bacterial load. Generally, the results indicated that total bacterial load and psychrotropic bacteria were more beneficial than histamine content to determine the reduction of fillet quality. It was found that histamine could not be regarded as a suitable spoilage parameter in trout as its level failed to achieve the European Community Standard of 100mg kg-1. The histamine increase rate was on the other hand highly dependent upon the total bacterial load, coliforms, yeast and molds, all of them can result from the rise in the content of this parameter during the spoilage process.

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