I think of it this way.
Two sheets of metal, between the metal are two ballons. You have 30lbs pushing down even across the metal. The ballons are going to compress to a certin spot then the weight will be transfered through. If you add one more pound of weight, the ballons will feel the weight. But the metal sheets have not compressed, only the ballons between them.
If water does not compress, it will transfers the weight of the air. Anything that is in the water that will compress. Like pockets of air or flesh will feel the pressure change. Since water is a liquid, then all sides of the fish will feel the effect, so it will be muliplied to some degree. I would assume that water some some small degree of compression, so deeper water would be less effected by air pressure. I know high pressure will push water down, out and away. And low pressure will allow for larger waves, like in hurricanes. So in my mind it only makes sense that changes in air pressure are felt by fish much better then some believe. I am a common sense type of person, not an expert on the subject. But if you push down on a hard object that has softer objects between you and the ground. The softer objects will be effected by the added pressure.