Ok first of in the US, WE DO NOT KILL ASIAN AROWANA THAT ARE SMUGGLED IN.
This is a rumor and a lie. Don't spread it.
There are several facilities that hold the animals as criminal evidence until trial. If some do die while being held, blame the idiots smuggling them. Protection of an endangered species is NOT a stupid law. It's the kind of law that needs to be in place to protect rare animals from money hungry idiots exploiting them for profit.
If you really are upset about the endangered status of the asian arowana, spend money to any group that is reintroducing them into the wild and doing a current wild population study to show they are making a come back.
End of story.