Aquatic mobs mostly tropical fish spawn uncontrollably

While working on a swamp that is mostly surrounded by oceans I started to have huge issues with performance. Tick rate would fluctuate between 5tps and 20 tps. When the game would rise back up to 20 ish tps the next lag spike would follow shortly after. Using gnembons carpet mod I isolated the problem being the game periodically spawning 500 to 1000 aquatic mobs and using carpet mods /tick entities i isolated that almost all of those creatures were tropical fish. Constant spawning and despawning destroys the server performance and makes the game basically unplayable.