I'm gonna politely and constructively add to your explanation of the round goby;
It has been so successful due to the abundance of resources it encountered. The Zebra Mussels were and are more of a secondary food source, as the Gobies are generalist predators. They did what many invasives do; they exploited a niche. The niche was a bottom dwelling predator, which had been filled previously by Cottus bairdii and various darters. What i'm saying is the gobies succeeded because they eat everything, not just zebra mussels.