At a glance explanation of fish fumigation, There are 2 main ways of fumigation that is usually done is cold fumigation (cold smoking) and fumigation (hot smoking), in cold fumigation the temperature of smoke should not exceed 400C, the best relative humidity (RH) between 60-70% . Above 70% the drying process takes place very slowly and below 60% the surface of the fish will dry out too quickly, the water content of smoked fish produced by cold fumigation is relatively low, so fumigation is mainly applied for the purpose of preserving fish (smoked fish are more durable than produced by heat fumigation). For more details you can learn in the fumigation application that I have provided in Playstore, thank you GOOD SUCCESS