Pebbles are a common substrate for captive aquatic environments such as fish tanks. For turtles, they're suitable only insofar as you can ensure your turtle won't potentially swallow some. They're functional as well as decorative, and they can serve as a substrate for aquatic and semi-aquatic turtles. Just be sure they are too big for him to scoop up with his mouth.
Pebbles are a kind of sediment known as gravel. Gravel includes a variety of stones, including pebbles, cobbles and boulders, that are classified according to size. A pebble, according to the United States Geological Survey, can be as small as 2 millimeters -- a particle barely larger than a grain of coarse sand. Pebbles can be as large as 64 mm, or 2.5 inches -- more than double the size of a newly hatched red-ear slider turtle and roughly half the size of many pet turtles. When shopping for a substrate for your turtle's habitat, focus on the actual size of the stones rather than what the packaging says, as your pet product supplier may not follow USGS guidelines in their labeling.
Most pet turtles eat a diet of commercial turtle foods sold in pet stores, but as omnivores -- consuming a wide variety of foods from plants to fish, tadpoles, worms and bugs in the wild -- some turtles are game to try anything. Whether hungry or simply curious, your turtle could potentially gobble up any object he finds in his tank, including pebbles if they are small enough for him to swallow. This could lead to serious health issues, including intestinal blockage and the need for surgery. If you wish to use pebbles in your turtle's tank, they should be at least the size of your turtle's head: too big for your pet to consume.
Your turtle spends much of his time in the water, but he needs to haul himself out of the water on occasion to sun himself and warm up -- because, like other reptiles, they do not produce their own body heat. You can facilitate them various ways, including using pebbles, as long as they are too large for your turtle to snack on. Grading the habitat's substrate, which can be made up of appropriate-size pebbles or an aggregate of large pebbles and sand, will create a dry shelf on one end, where your turtle can exit the water and bask, and a deep end where he can fully submerge.
Using a substrate in a turtle's tank, whether pebbles, sand or other material, is optional. Some turtle owners put a layer of large, smooth pebbles on the bottom of their pet's aquarium because it creates a visually appealing, natural-looking setting. In addition to the aesthetic benefits, a bed of pebbles -- appropriately sized for the inhabitants, can be functional because it provides a barrier between the turtle and the bottom of the tank. This barrier may be of benefit to some species of aquatic turtles, helping to prevent pressure sores on the bottoms of their feet.
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