Is catch and release fishing permitted? I've heard different opinions on this matter. Whats the official halacha?
Rav Moshe Feinstein has a great responsa in which he says that if it gives you pleasure you may hunt. Fish are generally considered to be lower life forms in that we grant fish fewer halakhic protections (for example eiver min ha'hai does not apply to fish). Though Rav Moshe does say in his responsa that it is not something that he thins is great to do it is not assur. Based on that I would say that in the case of fishing where the fish is not permanently hurt and that fish are generally afforded fewer protections it would certainly be permissible.
My sense is that Rav Moshe would not feel that C&R fishing would be considered unadvisable as he says hunting mammals is.
כי כל דבר שהוא לצורך האדם ליכא איסור צער בע"ח =בעלי חיים= דהא התירה התורה שחיטה ולא רק לאכילת ישראל אלא אף לאכילת נכרים מותר לשחוט, ואף לכבוד דאדם בעלמא
There are a number of opinions that state that catch and release is forbidden halachically on account of צער בעלי חיים - causing the animal pain.
For example, according to the Rav Menashe Klein, Zt"l - Mishneh Halachot - Choshen Mishpat - Chelek 12, Siman 432, it is asur (forbidden) to fish for sport if the fish will not be used for food, and even if the fish is released and survives, hooking the fish's mouth is asur because it inflicts tza'ar (pain):
The following internet sources also maintain that catch and release is forbidden:
HaRav Yitzchak Yosef Shelit"a holds it is asur to fish simply for pleasure. If I remember correctly, it is because of Saar Bale Hayim