I was end busting and placed water to MLG but I then went back into the end city because I saw another shulker. I went up without picking up my water because I thought I would just jump back into it once I got the final shulker but when I jumped back down I found four axolotls in the water I had placed. I had placed just a bucket of water not a bucket of axolotls, those were actually the first axolotls I found in survival. There is no explanation other than that they spawned in the water in the end. I do t know for sure but I am pretty sure that axolotls are not supposed to spawn in the end.