I don't know, but if you are growing illegal crops, then it is called as illegal. What I could say is every Government suggest to take care of environment. So don't think this is an illegal method of using Aquaponics.
I would say legal only, but in most countries people may to grow Marijuana which is illegal for them. I would suggest you to check your country laws and could you let us know from which country you are?
You need to contact nearest horticulture authorities , but in most cases it is legal only unless you grow illegal plants. Please c let us know your country and the plants you want to grow.
I don't think the method of growing a specific crop may be illegal, but the crops you are growing and what you are doing with them could possibly to illegal depending on how you got the seed(s).
