In practice, the time restriction for storage in ice often means that fishing vessels must return to their home port with the fish room partly empty. There is therefore a need for some means of preservation that will extend the storage life without substantially altering the nature of the raw material. Quick freezing and cold storage is an excellent way of doing this. When newly caught, fish are frozen quickly and stored at a low temperature on board, so there is no limit imposed on the length of voyage due to spoilage of the catch. Fishing vessels can remain at the fishing grounds until the hold is full. This increases the proportion of time spent at the fishing ground and improves the economics of fishing. It also allows the fish to be distributed to a wider market even without the existence of an elaborate "cold chain."

Fish which have been frozen at sea are of very good quality when landed; therefore, more time is available for the fish to be distributed over a wider area and still be in good condition. Freezing at sea has therefore an important role in world fisheries. A look at a map will show that large areas of ocean are far distant from any centres of population or even land, and many potential fisheries are therefore unexploitable without a method of preserving the fish for long sea voyages. Only quick freezing and low temperature storage has so far satisfied this need and, as traditional near water fisheries become overfished or are unable to satisfy the growing demands of an ever increasing population, freezing at sea will become more and more necessary. Sea-frozen fish, properly handled between landing on deck and loading into the freezer, when thawed are almost undistinguishable, from fresh fish kept in ice for a few days. The loss in quality as a result of freezing, cold storage and thawing is small when these treatments are properly applied. Thus, when very fresh fish are frozen at sea, the final product can be equal to the best on the market.