No, the Pope does not worship a fish god.
In the rush to denounce Tradition in the Church, some Protestant leaders have an unfortunate tendency to go a bit overboard. For instance, one of the most common (at least, “common” in more radical circles) objections is that, through certain liturgical customs, the Pope worships a fish god. While most would probably laugh at the thought, the allegation has been made on numerous sites.
First, there are many things wrong with that allegation, but I’ll start with the simplest one. Catholics do not “abstain from eating fish on all days except Fridays.” Many Catholics abstain from meat on Fridays and consume fish instead. This is a popular form of penance and sacrifice in honor of God, especially during Lent. However, there is no rule against eating fish on normal weekdays.
And as for the historical accuracy of their claims about the origins of the mitre, it appears that they just do not hold up to close inspection. For a relatively in-depth look at the history of the mitre, click here.
There is something semi-almost-but-not-really-accurate in the allegation, though: the Church does utilize symbolism.
There is a picture (taken by Alessandra Benedetti, it seems) in which you can see part of a papal chasuble with shell designs on the back, which a lot of the aforementioned Protestants point to.
Christianity has a close association with aquatic symbolism. The symbol of the early Church was the fish (the use of the cross did not come until later), St. Peter was a fisherman, and priests even use shells to scoop and pour water when baptizing, so shells also remind us of our baptism. To read about the origins of the Christian fish symbol, click here.
In conclusion, even if we make the false assumption that the Papacy is merely a temporal institution with temporal goals, it simply would not be in the Pope’s best interests to worship anything other than God. The Pope gets his temporal influence (what little he has in today’s hostile anti-religious environment) from Christians. Christians worship a single God in three persons: the Father, the Son, and the Holy Spirit (or “Holy Ghost,” if you prefer). Christians have no interest in supporting the idea of some random fish god. Therefore, the Pope does not even have a temporal reason to worship a fish god, as his power base does not want one.
The concept that the Pope worships a fish god is illegitimate and hardly constructive, and I hope that the few that believe it will drop it. It only serves as an obstacle in the way of meaningful ecumenical dialogue among believers.