Back in the 1949, a new product called "Friday Franks" appeared on supermarket shelves. You might be able to guess from the name that this was a meat replacement aimed at Catholics for a particular day of the week, but they weren't vegetarian. Nope, "Friday Franks" were made of tuna fish. 

Can you imagine? Maybe this excerpt from the Wall Street Journal can help: 

Friday Franks are composed of 100% tuna meat with a small amount of vegetable oil and spices for flavoring. No filler is added. The franks can be eaten either hot or cold. The tuna now being used is caught in New England waters. 

The original Friday Franks don't seem to have been all that popular, but that didn't stop another company, Bounty of the Sea, from attempting to produce a whole line of "hot dogs and assorted cold cuts made from tuna fish" in 1987. This time around, they were targeting dieters and other health-conscious folks, and the founder was optimistic: "We have the makings of a great new industry. I can see this being a $300-million company within five years."

Perphaps predictably, the trend never caught on, and the company went out of business by 1990. If you want to be the next chapter in this story and bring the trend back, you can purchase tuna franks on Alibaba. 

All of this history is from the great folks over at foodtimeline.org! I searched for ages trying to find some photos, but the internet is pretty dry for these sorts of things.