Couple things to think about when making fish stock..
1. Use Halibut bones if available. They're.. the best.
2. Use COLD water to begin with, and only let it boil once. Otherwise, you'll have solids that you'll have to strain out. After the initial boil, just skim off the top and you should be good.
3. This goes great with any seafood risotto.
=] thank the great chefs at Horizons restaurant, if you live in the lower mainland.