Fish stock, you only cook it for around 30 mins. I remember reading somewhere that fish stock loses flavor when you cook for longer times.

The ginger helps with the aroma. What fish are you using? In theory you could age the bones for a few days, since ultra fresh fish actually has less glutamates. You can also roast the bones to get some light color. Or add in some kombu for more umami.

I started spearfishing recently. All the "cool" people are dry aging their catch. I didnt realize aging increases glutamate content.