If you aren't familiar with the story, there is an illustrated version here.
The story was also made into a song by Avraham Fried.
The story is basically about a poor man who spent a lot of energy and money each week preparing for Shabbat, and HaShem rewarded him with a fish containing a precious diamond.
If the story sounds a little far-fetched, take a look at this incident that was reported by AP
The one that didn't get away yields long-lost ring
Wed Dec 3, 9:37 pm ET
BUNA, Texas – The one that didn't get away held an unlikely surprise for a Texas man. The blue-stoned class ring of Joe Richardson, engraved with his name, turned up inside an 8-pound bass 21 years after he lost it while fishing on Lake Sam Rayburn.
"My first reaction was — you gotta be kidding," he said Wednesday.
The fisherman who discovered the tarnished ring inside his catch contacted Richardson on Nov. 28 in Buna, about 100 miles northeast of Houston, after tracking him down with help from the Internet.
His fisherman hero asked to remain anonymous.
Richardson, 41, said he lost the ring about two weeks after his 1987 graduation from Universal Technical Institute in Houston. His mom had bought it for about $200 and wasn't pleased when it went missing.
As a mechanic, Richardson said he doesn't wear jewelry so he tucked the undamaged ring away.
"I have not cleaned it," he said. "I told my wife I don't want to clean it."
Information assist from KFDM-TV: http://www.kfdm.com