I have seen this several times on the net and it is just plain silly. The notion is that the mitre that bishops wear in the Catholic Church is actually a representation of the fish god "dagon".
Here is a sketch showing the evolution of the Mitre from the 11th Century onward:
Now, notice that the mitre has only been in use since about the year 1000AD, and that (according to wikipedia) the cult of Dagon disappeared about 500BC, how can bishops be referencing a pagan God whose followers died 1500 years before? It is ridiculous to think they are.
Here is also some good articles on the history of the Mitre:
Now can we stop this "dagon" nonsense? You have been educated.