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.
Veterinarians provide medical care to animals, particularly pets, zoo animals, livestock and laboratory animals. Along with diagnosing and treating illnesses, veterinarians may work as researchers or help control the spread of disease to humans through food.