Many turtles eagerly accept a variety of foods. They like to eat and will "run" over to you at feeding time. But their dietary requirements are quite strict and an improper diet will lead to early death.
Key to Health
Particularly devastating for these animals is a lack of the calcium required for both bone and shell growth. In order to metabolize the calcium, however, the turtle requires vitamin D3. While many species can utilize D3 that they get in food, others, such as desert dwelling species like the Egyptian tortoise, Testudo kleimanni, and confirmed basking turtles like the map turtle, Graptymys kohni, require sunlight or a full-spectrum light over their enclosure in order to produce the necessary D3 in their skin. As important, then, as how much food, are the kinds of food and supplements.
The Turtle Salad Bowl
In order to provide sufficient calcium, the salad forms a part of nearly every turtle's diet. This should be chopped finely and mixed (so the turtle can't pick out only the parts he likes) using calcium-rich vegetables such as dandelion, carrots, collard greens, bok choy, avocado, beet greens, cauliflower, endive and swiss chard. Add fruits such as blueberries, blackberries and cantaloupe. Cuttlebones, or calcium blocks, that your pet can gnaw on are available in pet shops.
For aquatic turtles such as the Florida softshell and slider species, the salad will be a side dish to its main course of fish, earthworms and crayfish. Trout chow, a prepared pellet of dehydrated fish meal, is a good diet for these turtles when supplemented with earthworms and greens. Prepare the trout chow by soaking the pellets so they will re-hydrate before you feed them to your pet.
Turtles, such as box turtles, that divide their time between water and land generally favor earthworms, fruits and insects such as crickets and mealworms. Most will also take trout chow that has been re-hydrated or prepared turtle chow. All of these should be supplemented with greens.
Forest and grassland species like the red-footed tortoise do well on mixed fruits and vegetables with a protein booster such as earthworms or commercial turtle feed. Desert tortoises such as the spur-thighed tortoise should be given timothy hay along with vegetables and turtle chow. This can be left in the enclosure for the turtle to graze on as needed. Too much protein can cause shell deformities in tortoises so give a bit of cat or turtle chow only once every four to six weeks.
How Often and How Much?
A turtle's stomach is about the size of its head. For most species, this should be the key to how much to feed each day. Most turtles, especially young ones, should be fed daily. For an adult box turtle, a day's food would be three tablespoons of the vegetable mixture and a couple of earthworms. You know your turtle is hungry when it begins to roam around its enclosure checking the place where you feed it.
Diet and Exercise
Although turtles have high metabolism they still need their exercise. In the wild they spend a good deal of their day searching for food. Giving them invertebrate prey such as earthworms and insects that they have to "hunt" will increase their activity level enough to keep them from becoming obese. How to tell if your turtle is becoming obese? Just like in humans his flesh bulges out, not from his beltline, but from his shell.
Proper digestion can occur only when temperatures are optimal. This depends on the species, but anywhere between 76 and 90 degrees Fahrenheit is appropriate.
Most turtles will get enough water from the aquatic area of their enclosures. Tortoises get plenty of moisture from the vegetables they eat, but a small bowl of fresh water is worth having in the enclosure.