Cut out sections of the wood and paste together for the walls, skirting and cornices (also cut out a hole for the window).
Also painted the walls and ceiling and overlayed on the walls.
Excuse the shadows, they were added later but onto the image rather than a separate layer (dumb I know).
step 2 of 3
Took a section of the fish and stretched out to make the 'operating table'. Also added some light and shadows - and the fish
step 3 of 3
Added the window from more wood from the source image, and a factory image masked behind (with a quick sign I made).
Also added the light box and the fish x-ray (which was inverted, and chopped)
Added the knife and adjusted the colours to make it greener to reflect the room.
After this all I did was some final colour adjustments and added some more highlights/shadows, and voila!