Why it takes shorter time to cook fish than meat?

It seems like it takes shorter time to cook fish than meat. Why is that?

Fish live in water. Fish's density is roughly the same as water. It takes less effort to support their weight in water than animals support their weight on land. Probably due to this, fish's flesh is not as tightly glued together as animal meat. That is why fish's flesh is easier to break down by cooking heat than the land animals' flesh.

Is that a reasonable guess?