how thirsty they were after walking so far. They were not able to drink from the walls of Red Sea water on either side since it was salt water.
Then, a fish out of a wall of water told Moses that he and his family heard the complaints of the people. Through their own gills, they could remove the salt from the water and force it out of their mouths to become fresh water for the Israelites to drink.
Moses accepted the fish's offer, but the fish and his family also had a demand: Their descendants had to be always present at the seder meal since they had a part in the Passover story.
Moses agreed to this and then said, "Go Filter, Fish!" To this day, this phrase remains the name of the fish (gefilter) eaten at Passover.