A lot of this advice is bang on, Ive done lots of canning fish and its great to have around to eat. You need to use a pressure canner. I've got two canners, both from the thrift store for 10 and 12 bucks and replaced the seals and they work perfectly.
Last year a buddy gave me some canned tuna he did with hot peppers, man that was good, gotta do the tuna this year.