You need to get special aquarium silicone, most LFS's will stock it. Shower silicone has fungicides and mildew repellants that will kill your fish very quickly.
If you can't rehouse your fry, lower the water to below the level of the leak, otherwise empty the tank.
Use a sharp blade to remove the silicone from around the leak, if you can, clean the surfaces where you are going to apply the silicone with a solvent of some type, acetone is the best you can use, methylated spirit would also work, and is probably easier to get hold of. (be careful not to get it in the water if you still have the fish in the tank)
Run a bead of silicone along the join, then smooth it in with your finger.
You are essentially done now, but leave the silicone to dry for 24 hours at least. It will smell very much like vinegar, it's meant to so don't worry.
When the silicone has set, start to refill the tank, SLOWLY! watch for leaks as the water level rises above the repaired seam.
You should be done by now. But keep an eye on the repair for a few days, just in case.
Hope it goes well!
