Indeed you can. As Dellannah noted, fish are just another harvesting node. You can harvest them on the island or in any zone that has water... which is like saying all of them!
Priests (and probably some finger wigglers) have a natural advantage in fishing since they get underwater breathing spells.
There are normally 3 different types of fish in each tier, however T5 seems to only have two. Regardless of the variety, heading out into the water near any dock/bell will get you access to more nodes than you can shake a pole at...
BTW - make food out of the fish and you will end up with +agi food. (And most scouts
+agi food!)