I would say someone with over 10 years of experience. In not only knowledge but also with practical experience in raising and taking care of rays of all kinds.
but then i have no experience with rays in the wild
also a Brazilian native may not have any idea how they breed as they probably haven't caught any rays when they are giving birth
experts in different Fields
rays in their native habitat
keeping rays
breeding rays
ray anatomy
I think an expert also is aware of how much they still have to learn. Once you close your mind to learning new things and consider yourself too much of an expert, you loose the ability to keep growing. Also- an expert should clearly state what is opinion based on their experiences and what is scientific fact. I agree with Matt that to really be a well-rounded expert you need to know some basic biology. You can probably be a great aquarist without a lot of knowledge, but to be able to really take your observations and apply them in the bigger picture, you need that foundation.
Not me im an armchair so the "experts" dont have to answer the .... can I keep a ray in my 55 gallon for life But i do try and learn what I can and add from what I have noticed about my rays
Not me im an armchair so the "experts" dont have to answer the .... can I keep a ray in my 55 gallon for life But i do try and learn what I can and add from what I have noticed about my rays