you then pull the drawbridges lever and make the bridges lower into the water,then rise and voila!you have fish.
Sadly, this is impossible. Drawbridges can't actually lift animals. As best, they can throw them sideways.
My last 40d fortress, before I stopped playing it through a combination of single digit FPS and the new version being released, had the following wonders:
Automated trash incinerators: A single-tile refuse pile in an elaborate mechanism. A dwarf walks to the refuse pile and steps on pressure plates that prime the system. The dwarf drops a piece of refuse on the pile, then walks out and steps on a different pressure plate that triggers the device. The machine seals the chamber, then dumps magma on the refuse pile. 100 steps later the magma is pumped back to storage, having ignited the refuse, which rapidly burns away and leaves the refuse pile clean and ready for use again. I had three of these running constantly to destroy chunks and other refuse.
Automatic animal breeding engine: A really elaborate machine full of wild rabbits (from the Dig Deeper mod). It used pressure plates with carefully chosen trigger plates to filter adult animals. Exactly a dozen adults would be retained in storage, and excess adults routed to a drop chute that would drop them onto a pile of weapon traps next to a butcher's shop. Baby animals would be stored in a waiting area until they became adults. Worked completely automatically, providing a steady supply of meat to the fortress. Later I built a second one using wild camels.
Invader killing mill: A 90 tile long three tile wide path covered with 9 10X3 retracting copper bridges, flanked by 10 Z-level deep pits on either sides. This normally served as the main entrance to my fortress. When a siege came, I would throw a lever activating an automatic repeater to the bridges. Goblins would run into the entrance and then be thrown sideways by the bridges, falling to their doom. The bridges were placed on a solid path so the pathfinding into the fortress would never be disrupted, so the goblins would never stop at the end and mill around like they will sometimes on basic retracting bridge over a pit design. This design won't work as well in DF2010 where the goblins come riding building-destroyer, bridge-immune mounts.
Brownian rachet conveyor belt: Underneath the entrance, I built an array of retracting bridges in a three-dimensional repeating sawtooth shape. Constantly running on a repeater, these would cause bodies and gear dropped into the pits to eventually be thrown to a safe collecting area deep inside the fortress. Unfortunately, this was a massive contributor to the FPS drain that led to me not playing this fortress anymore.
The Dwarven children's academy: I used pressure plates set to trigger for children but not adults and some floor hatches to route children into a sealed building. In that building I put everything the children would need - a stockpile of prepared food (dumped from above), and had a waterfall feeding multiple wells, a room full of beds, a dining room, even a tame dragon on a chain in the meeting room. A second pressure plate system would divert dwarves out of the sealed-off area when they matured to become adults. This kept children out of the rest of the fortress, safe and not underfoot.
Suspended animation chambers: In 40d there was a bug in which if you saved while a creature was airborne, there was a chance that when you loaded the game, that creature would be stuck permanently airborne forever. As far as I could tell, stuck airborne creatures didn't get hungry or thirsty or interact with the world in any way. So I build a single-tile bridge on a flat surface, lured an annoying noble there, locked him in place, then triggered the bridge repeatedly while saving and loading the game. Eventually the noble became stuck in the airborne state. Then I disassemble the mechanism and then surrounded him with glass windows. He never made another mandate for bismuth items, but I didn't get a replacement noble or the bad thoughts from killing him. I don't know if this trick is still possible in DF2010.