Fish breathing is medical slang for a sign of acute respiratory distress when a person gulps in air through his mouth in an attempt to breathe. It's so called because the opening and closing of the mouth resembles a fish periodically sucking in water. It usually means that something in the respiratory tract or the heart has gone horribly wrong (i.e. gunshot wound, multiple organ failure, pneumonia).
"The patient was fishbreathing when we found him, he turned out to have a GSW to the left chest with hemothorax. We drained out all the blood and sewed him back up but the injury went septic and he died the following morning."
A lawn breather is a firefighter that is breathing through his/or her SCBA (air pack) at unnecessary times, usually in the truck, or standing outside of the fire well away from the smoke and danger. Lawn breathers are normally frowned upon due to the fact, that when they actually have to go into a burning building, they only have 10 minutes of air left, and are the reason the entire hose/interior attack team has to be swapped out after only 5 minutes. Lawn breathers usually have fire department stickers all over their personal vehicles and multiple fire department t-shirts and hats.