This mod causes my game to have lag spikes. It also doesn't seem to make any difference in gameplay aside from the added technology. I still just have the typical basic fish, same as before. Maybe they respawn now? I don't know about the open ocean because I couldn't tell, but in some of the smaller ponds that I have been keeping an eye on, there are still no respawns.

https://imgur.com/a/ZO8PkbD
My in-game debug report (F4, F5) showed that the mod was adding 350 ms to the update cycle. I don't know much about scripting but I'd venture a guess that this mod is pinging a lot of the fish to make updates. Optimization in large game worlds is all about simplifying calculations, especially in things which are far away from the player. The script shouldn't need to periodically update each fish unless the player is nearby that fish; otherwise it should use a larger batch function and affect the fish population across a region, or something. Unfortunately I don't know any more than that about scripting.