IMO the invasives have now become the natives. No animal should be killed because it is in the wrong area. If he were to kill it and eat it that would have a purpose. Not senseless killing. You should treat them like native fish now. Yeah maybe he should not have brought them home but what is done is done. He now knows and it is his choice what he will do in the future. No sense in keeping on his case about it.
Thankyou for all the reply's, I can't believe how many views and replys I got from showing you the fish I caught, turned into quite the debate. I will no longer bring the fish home with me for pics, I will just take the picture like the Largemouth was taken. If I catch anything else interesting to the board I will post it. Thanks Again
You could always make a photo box out of acrylic if you really like to photograph your catches. It is just a fish sized box made from acrylic. There are pretty good instructions in Herbert Axelrods' Guide to Freshwater Fishes. The box will keep the fish still and you can photograph in sunlight. IMO, as long as the tank was clean, you just used a large photo box. I guess if you euthanized these fish, you would have to euthanize a lot of the wild fish photographed for books or magazines.