Can fish stock be left simmering for a long time without damaging the flavor? After reading this question regarding how to make a Cantonese fish soup I was considering adding an answer expounding on the fact that fish stock shouldn't be left simmering for too long, or you'll get a "glue flavor" in your soup because of bad tasting compounds being released from the fish trimmings.

However, upon googling for some sources to validate my claim I came upon this article, which among other things claims that


  If no flat-fish bones are used, the stock can cook for four to six hours; this slow cooking extracts all the gelatin from the bones and makes a wonderful, rich broth.


Is it correct that it is only certain kinds of fish / fish trimmings which will create a bad tasting stock if left to simmer for too long? If so, are there any other kinds of fish than flat-fish which can create this bad taste?
I am a European trained chef. This is a very interesting question and there are quite a few answers. In my opinion and experience, the simmer time of a good fish stock is 100% based on the type of fish bones that you are developing the stock with. I remember asking the question many times on my travels through Europe and North Africa. I will share my preferred methods for a few species of fish.


Turbot, 20 minutes after it comes to the boil, bay leaf only in the stock.
Dover Sole, a full mirapoix, simmer for 30 minutes.
Salmon, bring to boil and shut off, a full mirapoix is needed
Northern Hake, 45 minutes full mirapoix
John Dory, 45 minutes full mirapoix, white wine may be added if desired.


I hope that helps you out. Regards.

Michael