Pescetarians are vegetarians who do not eat any type of meat except fish.
It is allowed to do that for some time, but it is not allowed to claim that eating meat is totally harmful . The Prophets and infallible Imams (AS) used to eat mean and Allah (SWT) is ordering us to eat from the meat of the animal which we sacrifice (Sura Al-Hajj, Sura 28).
It is Makrouh (disliked) to eat meat daily for 40 days, and Makrouh as well to abandon eating meat for 40 days. The believers eat a little of meat even if they prefer vegetarian food, but claiming that eating meat is totally harmful contradicts with the Quran and teachings of the Prophets and Infallible Imams.