Modern fishing frequently does on-ship flash freezing and the results are often better than fresh fish. At least one reason is that the freezing kills parasite

Modern fishing frequently does on-ship flash freezing and the results are often better than fresh fish. At least one reason is that the freezing kills parasites. But also the fish will stay viable longer. The important detail is the method of freezing. Just tossing a fish into a regular freezer doesn't work. Flash freezing doesn't create large ice crystals which mess up the tissue.