Campaign Lore

After being stung by an aboleth's tentacle a humanoid who is unable to resist the poison or be otherwise cured physically transforms into an amphibious creature that is blindly obedient to the commands of the aboleth. The stung area will be a source of pain unless it is kept wet.

Someone who has been stung may resist the mind control by distancing themselves from the aboleth, but too much distance puts the person in mortal jeopardy. If they can succeed in maintaining this optimal distance then their life will be bound to the aboleth. None are sure what happens to the victim when the aboleth perishes. (See: Swamp Hermitess

...hapless humanoid creatures transformed by aboleths as their servants. A skum resembles a horrific combination of fish and humanoid. It has a slimy, scaly skin and a finned tail used for swimming. A skum attacks with its teeth and razor-sharp claws, or with any weapon provided by its master.

Sources

The Basic Fantasy Field Guide, Volume 1