Fish that has been previously frozen and thawed may be refrozen if it was thawed in the refrigerator and kept in a thawed state for no more than 48 hours. If the fish was thawed at room temperature or in hot water, it should not be refrozen.
If the thawed fish was kept below 40 degrees Fahrenheit or still has visible ice crystals, it is most likely safe to refreeze. Cold temperatures inhibit the growth of most types of harmful bacteria. However, bacteria may still develop in the refrigerator over time. Thawed fish should be either cooked or refrozen within two days of thawing.
The freezing process affects the texture of foods by breaking down the cell walls found in fish and proteins. Each time the fish is frozen, the structure of the protein is broken down more. Fish that has been thawed and refrozen more than once may have a mushy or unpleasant texture when cooked. Cooks may prefer to use refrozen fish in soups, stews or casseroles, since the texture is not as noticeable in these dishes.
Fish that was thawed in a microwave or cold water should be cooked before being refrozen. Fish kept at a temperature of 40 degrees or greater Fahrenheit for two or more hours is likely to develop harmful bacteria and should not be refrozen.