Although there are more than 200 species of turtles in the world, only about 150 of them make suitable pets. Sea turtles, giant tortoises and of course, the ever-increasing number of endangered turtles, should not be kept, even by the most dedicated hobbyist. The amount of time pet turtles can spend underwater depends largely on the variety of turtle, and whether he's in an active or resting state.
How Turtles Breathe
Turtles can go for long periods without breathing; however, they are not fish and therefore do not have gills with which to breathe underwater. Neither do they have diaphragms to force air in and out when above the water. Instead, a turtle pumps air into his lungs by moving his limbs and throat.
Most aquatic species, such as softshell and snapping turtles, spend most of their time underwater. The secret enabling them to remain mostly submerged is a special sac found on the inside of their throats called the pharyngeal cavity. When these turtles are resting or in a hibernating state, this cavity allows them to take the oxygen they need from the water. Some aquatic turtles can perform the same trick through the cloaca cavities located in their behinds. These respective types of breathing are called pharyngeal and cloacal respiration. Although species such as the softshell emerge only to lay eggs, when active, they do take air at the surface from time to time.
Semi-aquatic turtle pets, such as mud and musk turtles, tend to prefer a ramp up to a dry surface in their aquariums where they can bask in the sun or beneath a heating lamp. However, they can nevertheless remain submerged underwater for periods exceeding an hour. In fact, these turtles are likely to spend most of their time in the water, including feeding time!
Although it may seem strange, even terrestrial turtles can survive for longer than you'd think underwater. However, because they aren't equipped for pharyngeal or cloacal respiration, they have to rely on another clever turtle feature: a hermetically sealable shell. A box turtle, for instance, can remain immersed in water for up to an hour without drowning, simply by retreating into his shell. Terrestrial turtles all spend time in the water, some even mate in the water. But pet terrestrials must always have access to a dry perch.