Exie, by the first week, you get a sense of what the more popular fish are so learn about them, their environment, what their compatible with, their temperament and care requirement. These should be a minimum... Then you can branch out on the breeds and expand your knowledge that way as you would be building on what you already learned. Good luck. A new job is always exciting.
Unfortunately, the most popular fish are salt. It's a whole other world on that half of the fish room :p I am building on what I already know quite a lot, but salt is a different subject entirely.