Throwing in some local, small zoo experience here.
Years ago I worked for a rather small zoo, and only a few of the keepers had degrees. The owner was much more interested in experience, oddly enough, since overall zoo work is what I call the Elephant Experience: you canNOT be an elephant zookeeper unless you have experience with elephants, but you can't get experience with elephants unless you are an elephant zookeeper, overall. I did know a lead keeper who moved to INDIA for three years to work with elephants there, before coming back to the US, and with that experience under her belt, got a base job as an elephant keeper.
In short, my experience was with the freshwater and a few small marine tanks. A few sharks, eels, cichlids, etc. Nothing huge, perhaps the most exotic was the electric eel, and Fly River turtle. People wanted to see Nemo and Dory more than actual exotic fish.
The pay was almost minimum wage; most keepers only survived because they had wealthy spouses, or had a second job.
In this zoo, all keepers were hired (save for one or two) from the volunteer staff, and many people volunteered for years before an opening came. Why pay people when they will do the work for free? And since so many people want to work as a zookeeper, the pay could be kept low.
Don't get me wrong, it can be rewarding, but for a while I worked 40 hours a week at the zoo, and 20 at another job, just to make ends meet. Later I worked 40 at a retail job, and 20 hours at the zoo, and even then, the zoo pay covered a month of rent at most. You won't get rich, and there are a million people itching to take your job the second you screw up or mention you want more money or hours or to work somewhere other than the restroom janitorial.