While many old family recipes call for fish heads and bones to make your own fortified fish stock, there's a wealth of updated recipes that boast a more streamlined method for keeping the tradition alive with a lot less process, like these in Food52, Delish and The Spruce Eats, and this one from Williams Sonoma for Gefilte Fish Loaf that takes the simmering in stock step out entirely.
SAFE HANDLING — Keep frozen until ready to use. Remove from packaging and defrost in the refrigerator 8-10 hours before use. Do not defrost at room temperature. Once defrosted, do not refreeze and use within 3 days.