did they cause any problems? Economic impact or decrease in population of the Holy Trout from 8 years ago to today?

Invasive species suck and they shouldn't be there. No argument on that. I grew up during the Great Lakes invasive species panics... Zebra Mussels, Quagga Mussels, Spiny Water Fleas, Gobies.... and each one of them was absolutely going to be the ruination of the entire ecosystem.