Cats are obligate carnivores with an excellent sense of smell, evolved to eat freshly hunted meat and little else, who'll have to be very hungry before they eat anything remotely past due date.

We're omnivores who'll eat pretty much anything including stuff that'd kill most other animals that'd try to eat it (seriously, look up the long lists of “normal” foods you can't feed your pets because they'd kill them); we call deadly toxins that plants have evolved over hundreds of millions of years to be as inedible as possible “spices” and “drugs”, and consume them for fun. We'll let perfectly good food rot and ferment for months before we eat it because it somehow makes it better for our tastes.

No, we're most definitely not the picky eaters here, not even when compared to dogs, much less when compared to cats.

As for the ocean, everything in it comes with concentrations of mercury and other heavy elements and industrial waste that are harmful even to us, extremely high percentages of microplastics, and a vast variety of parasites that require anything we get from the ocean to be flash frozen before it can be considered safe to eat (if we ignore the heavy metals and plastics and other shit).

Plus, of course, every bit of crap ever produced on the planet ends up there... if homeopathy was real ocean water would be a fucking universal panacea, the amount of shit it's got dissolved in it.