The simple answer is no, dolphins don’t have gills.
In fact gills are actually a common characteristic of fish, sharks (a variation of fish) and a variety of amphibious creatures that enables them to pull oxygen directly out of the water so that they can breathe in an aquatic environment without needing to rise to the surface of the water.
Depending on the species some amphibians can breathe both underwater and on the surface, however most fish and sharks can only breathe underwater and unlike mammals fish would actually suffocate above the surface of the water.
In contrast to fish and sharks dolphins are marine mammals and must come to the surface in order to breathe.
Dolphins are equipped with lungs (like humans and land animals) not gills and would drown if they tried to breathe underwater just as a human would drown if they tried to inhale while submerged underwater.
In order to breathe dolphins swim to the surface and inhale oxygen through their blowhole, which can be found on the top of their head.
One interesting characteristic that separates dolphins from land based mammals is that unlike humans and land animals dolphins are incapable of breathing through their mouth because their trachea and air passage are not connected.
This serves several purposes for dolphins.
First of all having a separate trachea and esophagus allows dolphins to surface partially above the water while only exposing their blowhole, which makes it easier to breathe and allows them to rest without having to constantly monitor whether or not their head is above the surface.
If a human or land animal were to obtain oxygen they would have to lift their head completely out of the water which would take additional energy and require the animal to orient their entire body into a position where they can successfully breathe above the water.
A dolphin on the other hand can simply log around at the surface using little or no energy to acquire its oxygen.
Secondly, by having a separate breathing system dolphins are able to hunt for and consume fish and various other prey while under the water without the fear of drowning.
They don’t have to be concerned with opening up their lungs and accidentally filling them with water every time they hunt for fish and other prey.
Third, having a blowhole on the top of their head allows them to maintain good visual awareness of objects, prey and predators around them as they do not have to be distracted with lifting their head out of the water.
When it comes to breathing some dolphin species such as the killer whale may be seen spouting water from its blowhole when it rises to the surface of the water.
When this occurs the dolphin is simply blowing the water that has collected around its blowhole away.
It isn’t water that has been ingested through the mouth, lungs or blowhole as most people assume, its just water surrounding the outside of the blowhole that has been powerfully forced away when the dolphin exhales.
Before the dolphin dives back underwater it takes in a fast deep breath and closes the sphincter muscles around its blowhole to prevent water from getting in so that it can hunt and travel underwater without drowning.
The amount of time a dolphin can hold its breath for varies from one species to the next with estimates of 3 – 15 minutes being considered average for certain species.
In order for dolphins to stay submerged for extended periods of time certain unnecessary biological functions shut down to conserve energy and as much as 90% of the air a dolphin inhales is considered usable oxygen which is several times higher than that of a human and some land mammals.
Living in the ocean for millions of years has allowed dolphins to become extremely efficient at minimizing energy usage and maximizing the amount of quality air they inhale.
Dolphins are marine mammals not fish and like humans these marine mammals would drown if water entered into their lungs.
Unlike fish they cannot breathe underwater so they must come to the surface to get air.
In addition to helping them get air their blowhole also helps them survive in the ocean by minimizing the energy it takes to breathe near the surface, allowing them to maintain awareness of their surroundings and minimizing the chances of taking water into their lungs when consuming food underwater.
Dolphins have also perfected their ability to inhale quality oxygen and use it effectively in order to stay submerged underwater for extended periods of time, search for food, navigate the ocean or escape an attack from a predator.