My job requires me to shuck oysters I am not necessarily Buddhist but I am a vegan and killing doesn't sit well with me. I have suffered terrible sleep condition over the past 2 years and can't work in my field anymore and have no experience in any other field and have a hard time getting to work at an early time so midday work is best for me. Unfortunately the restaurant I work at currently has oysters for sale and they are alive when you prepare them which involves killing them. I don't know how to rationalize this but I am struggling financially and am working on getting a different restaurant job where they might not serve this dish. But I have killed some oysters already. How do I come to terms with this?
The Buddhist teachings do not exist for you to create suffering for yourself. Oysters are extremely primitive life forms. While they breathe oxygen, they are very close to plants. Oysters have a nervous system but not a brain. We practise non-killing as Buddhists so we cultivate a respect for life and cease to be violent people. If killing oysters (that don't suffer or don't have relatives or loved one's who suffer about them) is against your moral principles then find a new job. However, if you think deeply about what or who you have harmed, I don't think much will be found. Don't worry about it. Let it go. An oyster does not have a  brother, sister, mother or father somewhere in the universe grieving about their lost relative oyster. The Buddha appeared to infer in SN 12.63 that lifeforms consuming other lifeforms is part of the cycle of life. As a "vegan", I imagine your views about food are more extreme than the average Buddhist. For example, the Buddha did not preach vegetarianism. The above said, personally, I would not like to kill oysters for a living.