Primary keys are generally an attribute of the record that is unique to the record - something that is never repeated in any other record. I am not sure any of the fields you've named would be unique. Perhaps some sort of autoincrementing field could be used?
Species MIGHT be the PKF, but without the context it's impossible to say. I doubt it is tbh. What is the name of the table? What does the table contain... if it is something like a medical SAMPLE, then I'd suggest making a SampleID field that is set to Autonumber.