Ernie and Bernie are very close to each other and they are almost never separated. They love joking around and playing video games.
They used to be bullies and rather sadistic ones at that, shocking Oscar many times. However, they were also cowardly, begging Oscar not to hurt them when he pretended to kill a shark.
They were loyal to Sykes and eventually, they became friends with Oscar and quit working for Sykes. After this, they dropped their bullying and became nicer creatures, living at the Reef.