Gefilte fish (געפֿילטע פֿיש, German: Gefüllter Fisch, English: filled fish) are poached fish patties or balls made from a mixture of ground deboned fish, mostly carp (common carp). They are popular in the Ashkenazi Jewish community.
Sometimes, gefilte fish are found in patty form. The ground fish mixture is shaped into balls or oval patties and poached in a fish stock made from the head and bones of the fish. The poached balls are usually chilled and served with or without the jelled broth, accompanied by a horseradish-vinegar sauce known as chrain (either the red variety, flavored with beets, or plain white chrain, which has a sharper taste).
Commercial gefilte fish is sold in cans and glass jars, and packed in jelly made from fish broth. The US Patent #3,108,882 "Method for Preparing an Edible Fish Product" for this jelly, which allowed mass-market distribution of gefilte fish, was granted on October 29, 1963 to Monroe Nash.
There are even frozen and vegetarian variations.
Others say that fish are not subject to "ayin hara" ("evil eye"), so that a dish prepared from several fish varieties brings good luck. In the Bible, fish are symbolic of fertility: In Genesis 48:15-16 Jacob blesses Joseph and his sons by saying: "[Jacob] gave Joseph a blessing. He said, 'The God before whom my fathers, Abraham and Isaac, walked, is the God who has been my Shepherd from as far back as I can remember until this day, [sending] an angel to deliver me from all evil. May He bless the lads, and let them carry my name, along with the names of my fathers, Abraham and Isaac. May they increase in the land like fish.' "
Fish is parve, neither milk nor meat, and may be eaten at both meat and dairy meals (although some Orthodox Jews avoid eating fish and meat on the same plate).