Blue whales have a repertory system much like other whales. They have a blow hole at the back of here throat. This is how they breath. When a whale sends those massive water columns into the air they are actually expelling old air and refilling their lungs with fresh air. The average length of time a blue whale can hold it's breath under water is about twenty minutes but if properly motivated a blue whale can hold it's breath for up to forty minutes. The blue whale doesn't have gills which is why it has a blow hole. In fact all underwater mammals like dolphins, and whales have blow holes instead of gills. Blue whales though unlike humans do not have a trachea connected to the esophagus. The blow how is separate from the mouth and is there for less likely to choke on the water that enters the mouth when the blue whale eats. The blue whale who ever has two blow holes, one right next to each other. This feature is found mainly with large whales, given their large size requires large amounts of oxygen. This is a feature of baleen whales, whales that have baleen for teeth instead of real teeth. Most people believe that a blue whale shoots water out of its blow hole and this isn't exactly true. The water doesn't start out as water when the whale breaths. The air inside the body of a whale is very warm compared to the colder sea air. When a whale resurfaces the air that is release condenses and is turned back into water. The blow hole has another interesting feature about it. There are muscular flaps right on the inside of a whales blow hole that acts as a plug in the blow hole that keeps water out when under water. when a whale breathes it forces the muscles open and then once it has taken a deep breath it relaxes those muscles and dives back down, thus closing the blow hole and preventing water from entering. In all the blue whales repertory system is just like that of other baleen whales. it has the same set up and same function.