Combine fish, onion, parsley, lemon juice & salt in a heavy based saucepan.  Cover & steam mixture over a moderately high heat for 5 minutes.

Add water & wine & bring to the boil.  Skim froth off as it rises to the surface.

Simmer stock for 25 minutes.

Strain stock through a fine sieve into a bowl, pressing hard on the soilds.  Cool.

This is a simple, delicious stock which may be used as the basis for many soups.  It may be frozen.