Small flatfish and fish to be poached keep their shape better when gutted through the gills. Also, fish to be cut in steaks maintain their natural round configuration. Here, bream is shown.
Hook your finger through the gills and pull them out (they can be quite sharp).
With your fingers, reach through the gill opening and pull out the stomach contents.
With scissors, make a small slit at the ventral (stomach) opening and pull out any remaining contents.
Run cold water into the gill opening and out through the ventral opening to clean the cavity.