What is the opaque off-white layer settled to the bottom of my fish stock? Do you toss it or keep it for uses where you don't care that it's cloudy?

The writer has a fish stock with a cloudy layer on top, which is about 1/5 of the total volume. The cloudy layer has a sharp border with the clear stock below. The writer thinks the cloudy layer might be caused by albumin and suspended proteins that should have been skimmed. The writer notes that this cloudy layer only appears in fish stocks, not meat stocks. The fish stock was made by simmering fish bones, heads, collars, fins, and skin with mirepoix, aromatics, and vinegar for about 30 minutes. The fish used are from a lake, and there is a concern about PCBs in the wild fish in the writer's region. The authorities recommend limiting consumption of wild fish to a couple of servings a week. The writer wonders if the PCBs would be concentrated in the cloudy layer, and if so, whether it would be best to discard it. The writer is seeking opinions on what to do with the cloudy layer.