I bred to get a Greenfin Fatfish and have been unable to sell it for its list price of $800. Is this a mistake in the game or what? I have not been able to research advertising yet, could this have something to do with it? Help!

Which version of Fish Tycoon are you playing?

The online version

There are some differences in that version from the purchased game. One of those differences is a limitation as to what research you can buy, since the online version is really a demo of Fish Tycoon. You may have to lower the prices to get the fish to sell.