i dont see you know 3D modelling...
the fish tank is half transparent not 100% transparent thats why normally mmo engine dont support it
if all those holes are actual models which means it will need more polygons and will stress the gpu more, obvious less fps
the alex floor holes are not actual models but a flat plank, they are just texture that with 100% visible and 100% transparent, which called alpha map texture, it used on many things like grass, leafs etc...
https://docs.unity3d.com/401/Documen...Specular-0.jpg