There are three of them and they are all buff and strong. The blue fish is the tallest and wears white clothing. The green fish is the shortest and wears white and purple clothing. He has a black face mask on as well. Lastly, the purple fish is the most buff, and wears green.
Only one of them has been heard talking.
It is possible that they are only actors, as they are seen being knocked out by SpongeBob without a single touch.