I think they say it's not great to feed too much, and the article I've linked warns against 'tuna junkies' lol which I have one now. Sammy somehow knows there's tuna when we take it out of the cupboard, he's way ahead of the can opener.

So probably ok in moderation.

Here is a link that might be useful: catsplay.com article

This doesn't include tuna based canned cat foods does it?

Schoolhouse - maybe. There is a lot of debate about this. Cats are desert animals - fish is not a natural part of their diet. It may have too much of some things for some cats - like phosphorus from the fish bones for cats with touchy kidneys. Some cats get addicted to it and won't eat anything else. Fish by itself is missing taurine and some vitamins that are crucial. Commercial foods have those things in them.

I give my cat a tiny bit of my salmon 1-2x a week but her main food is the good-quality chicken/turkey canned foods. Doing that keeps her happy and healthy - and gives her something to do while I eat MY salmon. I am afraid she is very spoiled.

the primary problem with an ALL fish diet is the polyunsaturated fatty acids (PUFAs) in them (particularly canned fish meat without the rest of the fish) that can be very hard on cats, if not also supplemented with vitamin E. Cat foods containing tuna generally have plenty of the proper vitamin supplements to keep the excessive PUFAs from being a problem and get metabolized properly. I am not aware of problems with fish and feline kidneys, though excessive magnesium (present in large amounts in fish) can lead to crystal formation in cat bladders in those cats that have a genetic tendency to make crystals. Generally the canned fish diets have sufficient water to keep this from being a problem, but dry diets containing fish are one potential major contributor to some cat's getting cystitis (that is still not 100% proven), and even blocked (male cats only, thanks to their dinky urethras).

Thanks for the info. Hmmm, I also feed dry Taste of The Wild, Venison and Smoked Salmon flavor. Hope that's ok.