didn't Mary have a cat that lived till about 20 on sardines
Most people know of someone who lived into their nineties on a sixty-a-day habit, doesn't make tobacco any the less deadly.
It partially depends what the cat is getting elsewhere - some will hunt or scavenge others will not.
Susanne: Sea fish are high in sodium which small animals are sensitive to, and they contain little saturated fat which is an essential nutrient for felines. What are the sardines packed in? Brine means extra salt and plant oils cannot be properly utilised by obligate carnivores. Not necessarily the correct ratio of minerals to muscle meat. The cooked bones should be safe providing they are mushed up with the meat, as tinned fish bones tend to be crumbly not splintery.