Byzantine, Gothic and Early Renaissance paintings are rich in philosophical and Christian symbolism regarding fish.

The Fish is a very early Christian symbol used from the first century. The Greek word for fish, Ichthys, upon which a rebus ( word puzzle which uses pictures to represent words or parts of words) was created, is derived from the first letters of Greek words meaning "Jesus Christ, son of God, Savior."

Fish depicted in the Carolingian,  Byzantine and Gothic art periods are sometimes  symbolic of The Apostles. In the Bible the Apostles were referred to as "fishers of men".  Matthew 4:19 He said to them, "Come after me, and I will make you fishers for men." 

A "sacramental fish", accompanied by a carafe of red  wine and a basket of bread signifies the Eucharist and the Last Supper.

Dolphin - Symbolizes the resurrection, submission to faith, patience and mercy.

Sardine - Represents a peasant or man/woman of the earth, willingness of spirit, thankfulness.

Cod If a unmarried maiden is depicted holding a cod, maybe in a basket or bucket, this indicates she is designed for the nunnery or is a future saint. A soldier or member of the money positioned near a cod denotes a man of lustful ways. This could also symbolize a man in league with the devil or at the very least capable of devilish doings!

Shark symbolizes death, wanton destruction, cunning, a hunger for sinful doings.

Whale symbolizes obedience, willingness of spirit, gratitude, compassion, submission to faith, patience and mercy.

Fish in the Bible

 Mark 1:17: "Come after Me, and I will make you become fishers of men."

John 21:6: "And He said to them, 'Cast the net on the right side of the boat, and you will find some.' So they cast, and now they were not able to draw it in because of the multitude of fish."

Matthew 12:40: "...Jonah was three days and three nights in the belly of the great fish, so will the Son of Man be three days and three nights in the heart of the earth."  

Matthew 14:17: "And they said to Him, 'We have here only five loaves and two fish."

Corinthians 15:39: "All flesh is not the same flesh, but there is one kind of flesh of men, another flesh of beasts, another of fish, and another of birds."