Is fish-flavored cat food bad/dangerous to a cat's health?

Question

Our (two male) cats normally eat turkey and chicken flavoured canned wet cat food from our favorite cat food brand. However, we don't feed the cat's any other flavours which all contain fish, such as tuna or salmon, because of a vague recommendation from our vet:

"Don't feed fish-flavored cat food to cats, especially male cats. It's bad for them."

I attempted to find any evidence or statistics that any wet cat food causes any health problems of any kind in cats, specifically due to them having fish as an ingredient. Asking the manufacturer if the food has "safe" amounts of fish probably wouldn't be a trustable answer, either. Yet, this claim appears to be widespread and also very inconsistent:

http://www.justanswer.com/cat-health/2zknn-heard-foods-contain-fish-bad-male-cats.html

I have heard foods that contain fish are bad for male cats. It can cause damage to their colon.

http://answers.yahoo.com/question/index?qid=20101121172648AAd7Ny1

...male cats tend to have more UTI problems when fed a high amount of fish based foods. Its not really good to give fish food more then once a week.

http://ask.metafilter.com/175111/How-much-fishbased-cat-food-is-too-much:

Our vet warned us against feeding our cats too much fish-based wet food as we were dealing with Melon's second urinary-tract blockage.

http://www.catinfo.org/?link=cannedfoods#Ingredients

Fish and beef are common food allergens in the cat and can cause inflammatory bowel disease and skin allergies in some cats. ... If you want to feed a fish-based food as a treat, please limit it to once or twice a week.

http://www.catforum.com/forum/38-health-nutrition/98679-fish-bad-cats.html

I've heard that fish contains a lot of ash that can cause UTI's.

http://www.littlebigcat.com/nutrition/why-fish-is-dangerous-for-cats/

In general, the small amounts of “fish meal” included as a flavoring and/or source of omega-3 fatty acids in cat foods are not a problem, but fish should not be a mainstay of any cat’s diet.

http://pet.solazylife.com/cat-health/179.html

I would recommend avoiding fish flavored foods, which are said to be suspect in crystal formation.

At least one brand of cat food, and many others, use fish such as Tuna and Salmon as the main ingredient (not just a "flavour"). Given that this is true, the question is threefold:

1. Can any amount of fish cause health problems in cats?
2. If so, are there any observed amounts of fish that cause said health problems in cats?
3. If so, how does this relate to the amount of fish in canned cat foods?

Answer 1

I have a male cat that seems to have urinary tract problems all too often – not infection but blockage. After quite some time researching the problem and talking with vets and technicians this what I understand.

The problem is not seafood per se. The problem is the amount of magnesium in the food as blockages in the urinary tract are often caused by magnesium-based crystals. Seafood naturally has a higher level than meat but you can’t guarantee that all meat-based products are low in magnesium either. I guess we need to labels bores – check each one when buying to get the lowest available. For me that’s just an extension of my behavior anyway as I have to be very careful about what I eat too.

The other part of the equation is the amount of water the cat drinks. I know there is a vet posting somewhere on the Internet who makes it very clear that water intake is the most important factor. My problem child seems more interested in watching bubbles go around in the water than actually drinking it. I trick him a bit by adding water to his canned food but it’s still not enough.

One way to encourage cats to drink is to add the juice from a can of tuna or similar. Although they get a bit of magnesium I’m told by my vet it is outweighed by the extra water they get. Giving the cat moist canned food rather than dried food also helps with liquid intake. On the other hand some dried food promotes healthy teeth. I’m gradually moving my cats to the same diet with more canned food than dry. I also need to check the contents of the treats I give them to make sure that’s not a source of magnesium.

Hope this helps. Good luck.