Its water supply drains completely in eight seconds when out of a lake or an ocean. It moves slowly on land, too.
Sharks are large, bluish-gray animals, featuring two side fins and a dorsal fin on top, as well as an extended snout with small white teeth. They also have a thin, vertical oval for a tail.
As a Shark, you should always stay in an ocean. The ocean is your safe place; you move extremely quickly in the water and you can use your Speed Boost to escape your predators easily. If you are feeling bold, you can use your Speed Boost to bite a predator's tail, but it is very risky, especially with Krakens (their whirlpool ability can suck you back in when you try to flee after biting their tail).
If you are tired of staying in one ocean for so long, travel through a river. Rivers provide plenty of food, such as Mushroom Bushes and Clams. You can gain XP rapidly while traveling through a river. If a predator sees you and tries to hunt you down, dive underwater and use your Speed Boost, along with the river's current, to your advantage.
Consuming the food that spawns naturally in an ocean is not good enough. If you want to upgrade fast, you have to hunt other animals. Go for Octopuses and, if you find a Crocodile that is wandering around aimlessly in the ocean, go for it. Watch out for whirlpools (the ones that animals can hide in, not the Kraken's ability) and the Octopus's ink ability, which can help it escape from your sight while you are stuck and immobile for a couple of seconds. Lone Crocodiles are harder to hunt, as they can simply dive underwater and stay underwater until they reach the land and flee. Crocodiles can hold their breath for a very long time, more than long enough to reach the beach from wherever they are in the ocean. It's better to catch the Crocodile off guard so that it doesn't have much time to react. If you can't ambush it, just go for it straightforwardly and hope that it just tries to sprint away and doesn't dive underwater.
If neither an Octopus nor a Crocodile is available, just go for the animals that range from one to two tiers below the Octopus/Crocodile. Pufferfishes and Swordfishes still provide a decent number of experience points for a Shark.
Overall, just stay in an ocean most of the time. You should travel through a river to another ocean occasionally, too. Stay away from lakes and DO NOT go onto the land and you should stay safe long enough to upgrade to the next tier.