As mentioned on this forum a few other times in the past. your fish will maintain freshness depending on the temperature, the type of ice, as previously mentioned by Piperfelcher and how it is handled immediately after catching. If you are inquiring as to how to keep a couple of salmon fresh locally after catching....
Cut the gills immediately and let the fish "bleed out", clean the fish thoroughly. (leave the head & tail on)Place the fish in a large cooler,on top of an inch of chipped/cube ice, pack the cavity with cube or chipped ice and cover with an inch or two of more ice. You can then add a half dozen layers of newspaper if you want to keep the warmer temperatures of the cooler from melting the ice too fast...Your fish will keep for several day this way as long as you regularly drain the water.
Once home, I would eat or freeze the fish and consume it within a few months of freezing for best flavour retention.........Ortho 8)