Cats are different from dogs when it comes to their eating habits (and in many other aspects, actually, but that’s besides the point now). A dog would eat anything in his bowl, to the very last crumb, and won’t stop eating until it’s empty. A cat, on the other hand, has a sense of satiation, and it can take them a couple of days to finish the food in their bowl.
Cats are also more picky when it comes to food. While dogs would happily eat anything they’re offered, cats would only eat the best of the best. In this case, what could be better than a fresh fish? This cat decided he had enough of his cat food, and he was looking for a new, refreshing treat, right out of the ocean (or the next best thing – the bowl).