I am not aware of anyone in our circles who understands why Australian, Asian, African, or SA black arowana are any different with respect to a potential effect on the Florida ecosystems than the SA silver. I get your question. Black and silver are like GMC and Chevrolet, or six one way and half a dozen the other.
I have never met an explanation. Not that I looked anyway. The government doesn't have to explain but I am sure if one digs up the legislation papers, something could be understood. I for one have better things to do as doing something like this sounds as exciting as a short and senseless jail sentence to me personally.
That was my thought too. black and silver aros are the same to me except for their scientific name and coloration.
I even think the ban on asian aros is ridiculous. Since 99.9% of all asians on the market is farmbreed and has to come with legit papers and a microchip just like any purebred dog or cat. But thats for another discussion IMO.