Was fish served at the last supper?

No. At the Last Supper, also commonly called The Last Passover, Jesus and his apostles celebrated a yearly event that Jews and Israelites had celebrated since the day they were release from slavery to Egypt in the 1500's BCE. This yearly memorial, called the passover, was instituted in Exodus chapter 12, and there God commanded the Israelites to take a sheep (or goat) to sacrifice. The Israelites continued in this tradition down to Jesus' day.