Certainly a gray area, however, generally these fish would be wild. Perhaps right at the time of release, when they are still present at the release point where humans did place them, they would not be wild. However, as soon as they are freeswimming and choose a new location for themselves, they would be wild. Of course, identifying exactly when that happens is squishy and people’s opinions may differ. In this specific case, the release was not intentional by humans either!
For the plant scenario you present - if a plant was planted in a specific place by humans, it is cultivated regardless of how long ago that was or whether it remains under care. A pine plantation for instance would not be wild regardless of the age of the stand.
There are a fair amount of threads that deal with the huge variety of wild/not wild scenarios, so if there’s a specific case users are interested in, it can be worth taking a look at those. For captive plants some are:
https://forum.inaturalist.org/t/trees-that-were-planted-but-growing-in-wild-should-be-considered-wild-and-additional-grade-for-grey-zone-is-required/26777
https://forum.inaturalist.org/t/clonal-plants-descended-from-a-captive-cultivated/49240
https://forum.inaturalist.org/t/are-the-standards-of-what-is-considered-cultivated-different-from-captive/46296
https://forum.inaturalist.org/t/restoration-project-plants-be-marked-casual/43856
though there are so many others, I can’t keep track!
Moderators can open those threads up if there’s additional discussion needed.