Default Minecraft does not compare to what Loka has to offer when you go fishing. Grab a pole, though some stat tracking on it and head on down to Frodii's Fishing Tournament!
When a fish is caught, it will have a weight to it in its description. It can wary from 1oz to 250lbs, 250 lbs being the maximum size a fish can have. The person that hands in the largest fish in spawn would get Master Angler title before his name.
Fishes also are limited to continents. Each continent has its own fish.
Kalros - Salmon
Ascalon - Normal fish
Garama - Puffer fish
And occasionally goldfish can be caught on all three continents