A little boy once returned home from Hebrew school and his father asked, "what did you learn today?"
He answered, "The Rabbi told us how Moses led the children of Israel out of Egypt."
The boy said "Moses was a big strong man and he beat Pharaoh up. Then while he was down, he got all the people together and ran towards the sea. When he got there, he has the Corps of Engineers build a huge pontoon bridge. Once they got on the other side, they blew up the bridge while the Egyptians were trying to cross."
The father was shocked. "Is that what the Rabbi taught you?"
The boy replied, "No. But you'd never believe the story he DID tell us!"
As Moses and the children of Israel were crossing the Red Sea, the children of Israel began to complain to Moses of how thirsty they were after walking so far. Unfortunately, they were not able to drink from the walls of water on either side of them, as they were made up of salt-water.
Then, a fish from that wall of water told Moses that he and his family heard the complaints of the people, but that they through their own gills could remove the salt from the water and force it out of their mouths like a fresh water fountain for the Israelites to drink from as they walked by.
Moses accepted this kindly fish's offer. But before the fish and his family began to help, they told Moses they had a demand. They and their descendants had to be always present at the seder meal that would be established to commemorate the Exodus, since they had a part in the story. When Moses agreed to this, he gave them their name which remains how they are known to this very day, for he said to them, "Go Filter Fish!"