Process fresh salmon into Sushi / Sashimi salmon?
Sushi fishes are usually flash frozen for a few days before being used for safety (to kill off bugs)
It might change the texture of the fish as it is unfrozen; the better the restaurant the better the fish will be unfrozen.

http://www.pbs.org/food/fresh-tastes/myth-sushi-grade/


  For fish that contain parasites, the FDA provides guidance under their
  Parasite Destruction Guarantee. This states in part that fish intended
  to be consumed raw must be “frozen and stored at a temperature of
  -20°C (-4°F) or below for a minimum of 168 hours (7 days)”.


As for the fluid, I don't know, maybe fat or just water with dissolve fish protein (the thing that turns white when you cook salmon).