I've devised a simple fishing system that isn't complete grinding. What I did was make a small 16x16 pond. In this pond, there is a grid of 4x4 plates. Each plate randomly sets a FXswirl droplet emitter, and enables raycasting and a certain event. Thus, when a player sees a fish "surface", he must spear it within 250ms. It's not extremely challenging, but it's more fun than circling the same pond for 6 hours catching fish as they respawn. I used a modified LEGOKnights spear that must be charged completely. IT makes an interesting challenge.
Each fish you catch gives you 1 fish, and .1 FishSkill. Skill isn't used for anything other than a statistic so you can measure what you do most often. I might make so some ponds are harder and give you higher skill per fish caught, and/or more fish per fish caught.
I have a server up where I'm running some ideas through, the password is asswor if you're interested.