The first time you turn in a stack of 20 fish at the Tuskarr Fishing Holes for the Catch and Release quests, you receive 100 Iskaara Tuskarr reputation for the five normal fish (Scalebelly Mackerel, Cerulean Spinefish, Aileron Seamoth, Thousandbite Piranha, and Temporal Dragonhead), and 200 Iskaara Tuskarr reputation for a stack of 20 Islefin Dorado. This was added recently as another way to earn Tuskarr reputation.
What you might not know is that you can repeat this every week!