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Food
Tortoises are most active during early morning or late afternoon. Underwater observations throughout Australia have shown that these are the times when most food is taken. During these hours the water is clearest, as the sun is not directly overhead and therefore does not cause a hazy effect below the surface. Feeding does not continue throughout the day, but to a lesser extent.

At times tortoises leave the water to bask on a protruding rock or log, but they are always alert. Their eyesight and hearing are acute and at the slightest unfamiliar sound or movement they will drop gracelessly into the water and swim for safety.

When the sun is highest, tortoise numbers appear to dwindle. They are always more apparent along a shaded stretch of water than in the areas exposed to direct sunlight. Shaded banks are probably selected for the security they afford.

Tortoises' food preferences vary slightly depending on the species and the food available, but all tortoises appear to thrive on a similar diet in captivity. Some hatchlings feed on mosquito larvae, small crustaceans such as water fleas, and weeds. But some do not eat for some time, as they are sustained by a supply of yolk which remains attached to the plastron. This is a very tender area and care should be taken when handling hatchlings in this condition. The long-neck tortoises (especially the Broad -shell Tortoise) are known to have the largest amount of yolk attached on hatching. Hatchlings of all species from artificially incubated eggs showed greater evidence of this yolk retention than those hatched under natural conditions.

Adult tortoises in the wild feed largely on molluscs, crustaceans and aquatic insects. A large short-neck tortoise crushes small mussels in its powerful jaws. The thin tapering edge of shells of larger mussels is snapped by the tortoise's jaw-this eventually causes the shellfish to die, and when the shell relaxes the mussel is eaten. Tadpoles, frogs and small fish are included in the regular food supply and carrion (dead fish and animals) is also eaten.

All Australian tortoises include some plant matter in their diet. In districts where the introduced Water Hyacinth is abundant, the bulbs and purple flowers of this floating plant are regularly eaten. The Pig-nose Turtle feeds on the ripe fruit of the Pandanus or Screw Pine which drops into the water from overhanging plants. Water weeds are eaten occasionally by all species, and algae are on some species' diet.

The stomach contents of two Broad-shell Tortoises from the same small waterhole showed that one was feeding exclusively on shrimp, the other only on small fish. A Krefft's Tortoise from the same pond ate the fruit of wild mulberries. The Elseya Dentata that were present ate algae. Elseya Latisternum ate weeds and Chelodina Longicollis ate larvae and small crustaceans.