Yes you can.  It is safe to can frozen tuna.  I would not thaw it completely.  Thaw until you can easily cut it and then pack it into pint or 1/2 pint jars.  I find if I completely the fish then you lose quite a bit of liquid from the fish since freezing breaks down the cells.  If it is completely thawed the fish might end up being a little on the dry side since you pack it without any added liquid.  If it is completely thawed you could add a Tablespoon of water or oil to each jar.

Be sure to pressure can it for 100 minutes at 10# weighted gauge or 11# dial gauge canner.

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Nellie Oehler