But, frankly, I’d go with something totally different like he treaures this goldfish to himself for years, looks after it all, is the only one to see and appreciate it, spends lots of time loving it, and when it dies no one else knows why he’s so upset and he got much more than his money’s worth out of the fish because he treasured it so highly (worth/value is individual, you can’t explain what is worthless to one person is valuable to someone else, only you see the worth in things). Why shouldn’t he keep the fish to himself? It makes him feel more special about it. I would squeeze every penny out of specialness out of the fish if I spent all my money on it.

your story sounds like something that’d be the same as “The necklace” by Guy de maupassant. why don’t you try getting an idea from it?

it goes like this:
A french husband and wife borrowed an expensive looking necklace to the wife’s friend so that they could attend the ball looking elegantly. the wife is ambitous, but they didn’t know the necklace is a paste.

they lost it during the ball. and then they didn’t admit it at first to the wife’s friend. they tried doing something to cover it up.. the biggest thing they did was to see a real and expensive necklace that looks exactly like it. they worked so hard for many years to buy it.. and after that, only they found out upon admitting to her friend that it was their biggest mistake not to admit what they’ve done and cover it up…. =)