Why can't certain cells, like bacteria, get to be the size of a small fish?

The fact that surface area to volume decreases as size increase. There is a limit to this ratio where the surface area can no longer be sufficient to provide nutrients, ions and other things from the outside environment to the inside. Eukaryotes compenaste for this by having organized organneles and they tend to work together to form tissues and then organs.

The fact that surface area to volume decreases as size increase. There is a limit to this ratio where the surface area can no longer be sufficient to provide nutrients, ions and other things from the outside environment to the inside. Eukaryotes compensate for this by having organized organelles and they tend to work together to form tissues and then organs. I hope this helps:)