or at least how i did it... you can also buy washer shaped magnets (with a hole in the center). those could be sewn onto the inside body of the fish with a few stitches. or you could even use a large washer in the fish's nose (and just have a magnet in the worm). i put round magnets in both the fish and the worm. and i wanted them to stay in the fish's nose so i sewed them into little pockets.
magnet completely stitched into two layers of thin recycled wool.

i put the encased magnet in between the nose of my blanket-stitched fish.

...and continued stitching around nose through all four layers of wool
(inner covered magnet and outer pieces of wool).
then, finish stitching all the way around leaving a small opening to stuff with wool. use a small dowel to move wool into ends. and stitch closed!

same thing for the worm. all important: finding the perfect fishing pole (i.e. stick).

more to share too! it's just taken me over two weeks to write this post! i'm belated-ly linking up with
julia's
sewing bee thursdays.