You can work at an animal shelter or nonprofit.
You can work at a zoo.
Veterinarian - requires college degree (4yrs) and vet school (additional 4 yrs during which the first 2 years is spent in the classroom and the last 2 years is spent doing clinical rotations)
Veterinary Assistant - requires high school diploma
Veterinary technicians - performs medical testing and diagnose injury/illness; requires college degree and board certification exam
Wildlife Biologist - requires college degree and a master's degree for more advanced positions; PhD for research work or to be a professor
Marine Biologist - similar to above