It's been said that fish and houseguests stink after three days. While the science of chemistry can't help you get rid of a visitor overstaying their welcome, there is a way to get rid of the fish stink. It's important to know where the stink comes from. It's a chemical in the fish called trimethylamine oxide, or TMAO. It's odorless, but as soon as the fish is caught, bacteria break it down to TMA (losing the oxygen and intensifying the amine) and this causes the stink to rise.
It's possible to de-funk the fish. The first thing to try is a cold water rinse. This washes off the bacteria and the TMA and freshens it a bit. Cold water only, hot or warm water will only cook in the smell. If that doesn't work, a milk soak of 20 minutes is a good trick. The protein casein in the milk attaches to TMA and lifts it out like a can of Funk Be Gone. Finally, if all else fails a nice acid bath might do it. TMA molecules are basic and can be neutralized with the acid of lemon juice or vinegar. When the smell goes, so does any nasty less than fresh taste. Fish is best when it's fresh, but in case you have one hanging around, try chemistry!