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.
And of course, the surgery may be long, intricate, and complicated. Your veterinarian may work with traditional scapel and suture or use the latest in electro-cautery, lasers, and maybe even remote, micro-surgery techniques. Your veterinarian may be a general practioner or a board certified surgeon with 3-7 years of post doctoral training.