My cat loves tuna. So do the ants. The solution to the ant problem is to put a water moat around the cat food bowl.
Starting with the stainless steel bowl for the tuna, I found that it fits perfectly inside the plastic container that CDs come in. For the feeding bowl you use, you may need to find a different container it will fit into. That container, in turn, needs to fit inside another plastic container. Leave an adequate distance between them for the water moat. The moat has to be wide enough that an ant can not reach across it without swimming, which they tend not to do.
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A few dabs of epoxy glues the center container to the base of the outer container. It will stay centered and not float around when the gap between them is filled with water. That is all there is to it. It is a very simple thing to make once you find the right size containers to make it with.