An article link "Eight Strikes Against Fishy Feeding: https://catnutrition.wordpress.com/2007/09/22/eight-strikes-against-fishy-feeding-for-cats/
an excerpt: ... Fish, with its high magnesium content, can contribute to a type of urinary tract problem in cats. ...
Urine crystals are caused by magnesium (yes, and too little moisture)
Fish have a decent amount of magnesium
So, if your cat begins having issues with crystals in the urinary tract - look to the diet of fish as being a big contributor in this painful health issue.
We have 12 living inside with us - with various health and feeding issues - so our house has "cat zones".
Five of the cats are still mostly feral-like which contributes to additional considerations. We also take care of 5 feral-born that live on our property and in our garage. If I could...
Good Tips, but not relevant to me - we have too many cats to do anything but have food and water available for them - so, I've given up on planning anything else. Like - which cats do I actually pick to live? I think I'd rather just die with them.