The safety of these limits is again dependent upon proper handling at sea. As previously mentioned, recontamination with enzyme-forming bacteria and significant temperature abuse is necessary for histamine formation under these conditions. It is an effective means of detecting fish that have been subjected to a variety of abusive conditions. However, odors of decomposition that are typical of relatively low temperature spoilage may not be easily detected if the fish has undergone high temperature spoilage. This condition makes sensory examination alone an ineffective control for scombrotoxin.
Chemical testing is an effective means of detecting the presence of histamine in fish flesh.
However, the validity of such testing is dependent upon the design of the sampling plan. For this reason, chemical testing alone will not normally provide adequate assurance that the hazard has been controlled. Because histamine is generally not uniformly distributed in a decomposed fish, a guidance level of 50 ppm has been set. If 50 ppm is found in one section, there is the possibility that other sections may exceed 500 ppm. Additionally, recent studies suggest that if histamine production is advanced, histamine formation can continue even in frozen storage.