Okay, I have some results after I tested to see what would happen when you stock foreign fish into an existing pond. The fish you stock with do not add on to the current spawner but form their own. For example, what I did was go to Central Park (is it Central Park?) in the middle of SV and I clicked the option to stock fish where fish were already active (the minnows, goldfish, lobsters, etc.) and chose to stock crocodiles. However when I inspected the water, the crocodiles were not with the other fish and were not active. So, when I inspected one patch, it would say active and then you could catch minnows, goldfish, etc. Move a very little bit away from that and inspect it again, and I found that it said decent place to fish, and only crocodiles are available to catch. Does this makes sense?