A Philistine deity represented by the fish emblem is Dagon. The name means "corn," Dagon is an ancient Mesopotamian vegetation god, father of Baal. According to myths he was the god of crop fertility and the inventor of the plough. He passed this knowledge to mankind to let them better till the soil and produce food. Dagon's temples were in the cities of the Philistines for 2000 years. Dagon's temple at Ashdod still existed right up until the time of the Hasmoneans [who ruled parts of Palestine in Jesus' days]. Dagon was portrayed half man and half fish.
As far as the Bible goes, The Most High God has had conflict with this false idol at least since the times of Samson. In Judges 16 is the story of Samson, after the Philistines bound him, they had a party they praised Dagon because of the arrest of Samson.
In 1Samuel 5 during the days of Samuel the priest, the Philistines waged war against Israel. During the battle the ark of the covenant of God was taken by the Philistines and brought to a Philistine city called Ashdod. There the ark was set up in the house of Dagon, next to the idol of Dagon. What happened next is a testament of God’s fury towards this fish emblem.
“When the Philistines took the ark of God, they brought it into the house of Dagon, and set it by Dagon. And when they of Ashdod arose early on the morrow, behold, Dagon was fallen upon his face to the earth before the ark of the LORD. And they took Dagon, and set him in his place again. And when they arose early on the morrow morning, behold, Dagon was fallen upon his face to the ground before the ark of the LORD; and the head of Dagon and both the palms of his hands were cut off upon the threshold; only the stump of Dagon was left to him. Therefore neither the priests of Dagon, nor any that come into Dagon's house, tread on the threshold of Dagon in Ashdod unto this day. But the hand of the LORD was heavy upon them of Ashdod, and he destroyed them, and smote them with emerods, even Ashdod and the coasts thereof. And when the men of Ashdod saw that it was so, they said, The ark of the God of Israel shall not abide with us: for his hand is sore upon us, and upon Dagon our god” (1 Samuel 5:1-12).
When they moved the ark to a different city, the Bible says that the men of that city received emrods in their ‘secret parts’!
Note: an emrod is similar to a tumor. Some scholars say that it was a case of bubonic plague, while others argue it was closer to hemroids.
Either way, it is the penalty for mixing the holy things of the True and Living God with the house of dumb idols.
I wonder if the men of the city got up in the morning, saw their idol face down and instead of 'cursing' said, "Dag-gonit!" In the case of a Christian, I personally think that you'd be better off cursing, rather than speaking the name of a false idol/pagan god and offending the True & living God, rather than saying a word that might offend a couple of people.
This folly was instituted under the catholic church. It should be therefore no suprise that the dress of arch-bishops, cardinals, and even the pope resemble the garments worn by the priets of Dagon (and even Dagon himself) in the Babylonian Mystery Religons.
The youtube link better illustrates this point. (@ 2:58)