It is absolutely correct that marbled crayfish (Marmorkrebs) were found by hobbyists first, who introduced them to scientists second. The only known wild populations are where they have been introduced by people.
There has never been any serious suggestion that someone specifically bred Marmorkrebs. If it was a pet owner, you would think that person would want to take credit, as pet owners are often proud of such things.
Asexual species can be bred from scratch in the lab, but it seems to be incredibly
hard. One research team, working on asexual lizards, tried to do this for 29 years, failing all the time, before another team succeeded. Marmorkrebs: Celebrate diversity: Instant whiptail!
Much more about this on the research website I run, http://marmorkrebs.org