Unbalanced.

The lower leveled sharks last longer, and the higher leveled sharks struggle to survive. For a comparison, the lower level sharks tend to last around a minute without eating, but higher level sharks must continuously eat or die after around 20 seconds. Also, the higher level sharks should earn more currency. What I mean is to have a % bonus depending on the max health of the shark. That way, the higher level sharks can earn a bit more to help earn enough to get the upgrades.

-E135- about Hungry Shark Evolution