Leave it outside in the sun for a week to dry then wrap it in a cloth and call it an egyptian mummyfish.
Poke it with a stick and sell it as a dead vampire fish.
Shoot it in the head and sell it as zombiefish that you only barely managed to kill before it started the zombie apocalypse.
Replace it with a similar living fish and sell it as a resurrected jesusfish.
Dye it green, sell it as an alienfish.
Dye it green and sell with a goldfish bowl full of goldfish as a leprechauncichlid.
Burn it to ashes in a fireplace then sell the ashes as a phoenixpleco
Before it dies put it in a blacked out box, sell it as schroedinger's catfish.
Sell it as a live fish that does tricks and is really really really good at playing dead.
Roll it in glue and then lots of cat/dog fur and call it a werewolf cichlid.
Sell a dead yellow fish as a blondefish, drowned to death.
Throw it as high as you can then sell it as New Zealand's first attempt at a fish astronaut(Failed)
Send an empty box and insist it's a black ghost knife fish and you just aren't open minded enough to see it.
Midas cichlid, started changing everything in its tank into gold, decided to keep it.