Plankton is not the name of a plant or animal but more of a category for any drifting organism that inhabits the middle to upper levels of the ocean, namely the pelagic zone.
Most vets do spays, neuters, bone surgeries, spleen surgery, tumor removals, and intestinal surgeries. Heart surgery and more complicated surgeries are done by specialists that requires more schooling. If you want to be a vet, you have to have REALLY good grades and Vet school is MUCH harder to get into than human medical school.
Zoo veterinarians provide both emergency and routine medical treatment to the many species of exotic animals kept at zoos. By observing an animal's behavior and providing a physical examination, a zoo veterinarian can diagnose illnesses, learn the extent of injuries and provide treatment.