Fish (물고기, mulgogi) appear elsewhere on this site specifically in the taemong (conception dream) context, where catching a large fish points to a capable, resourceful child. Outside pregnancy dreams, a general fish dream is read more broadly as opportunity or wealth swimming toward you.
Catching a fish, especially a large or lively one, is read as successfully securing an opportunity that required real effort — fish, unlike money simply appearing, generally have to be caught, and the dream's reading reflects that active effort. Catching many fish at once is read as a period of unusual abundance rather than a single win.
A fish escaping your grasp or slipping out of a net is read as a missed opportunity, close to the same reading a slipping-away pig or rabbit gets elsewhere in this category — something you were close to securing that got away at the last moment.
A fish jumping out of the water toward you on its own, without any effort on your part, is read as unexpected, low-effort luck — good fortune that arrives without you having to chase it down, a rarer and generally more delightful version of this dream than the effortful catching variant.