The Tidepool

This is my favorite species of polychaete worm btw

Fun fact: this fish has my favorite color scheme and pattern combo of any animal

This is very delightful and whimsical

Hi, fish nerd here. So, the way that gills work is that as water passes over them, the oxygen kinda just diffuses into them, and carbon dioxide is released. For this to work, they need a high surface area. Gills can actually take oxygen from air just as well as water, but only if they remain wet and don't collaspe onto themselves. As for the other two questions, fish can be "out of breath" so to speak, especially if the water they're in has too little dissolved oxygen. This is the reason many unrelated fish have independently evolved air breathing, as they live in waters with low or inconsistent oxygen levels. Some fish are also very active, like tuna for example, and they can get exhausted if they keep up a chase for too long. Fish cannot hiccup, that happens when your diaphragm is upset, and that muscle is exclusive to mammals. But the way some fish breath does resemble a hiccup, as they suck in water to pass it through their gills. Hope this helped!