It is a real slaughterfish and real in game screenshot.
If you want one then you will need Darknuts slaughterfish replacement texture from his http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=5980
The rock texture background is an experimental texture i made , which looks good in places when close up and at the right angle , but otherwise not really suitable as a world replacement texture as it doesn't look good when it tiles due to the large distinctive rocks. If you do use it then i suggest take a copy of your regular coastal rock texture first as you will probably want to restore it after , assuming you want to try http://www.freewebs.com/slartibartfast1/FWThumbnails/tx_coastal_rock_01.rar
if you are using Texture Fix version 1.8 you should be able to find plenty of opportunities to take similar screenies in the water south of pelagiad , by Suran and Dren plantation areas.
Happy Fishing.