Start with a good stock. I only started making it 2 years ago, so I don't have it perfected yet, but it's good. Keep in mind, I cook a lot, don't eat processed foods, and enjoy doing it. Sorry, I don't have exact amounts. I can repost this with some measurements if you're interested after I catch some fish. I cook by sight and taste.
For the stock, when I clean all my fish, I fillet them out and save everything but the guts and gills. I take all the normal "waste" and throw it in a big pot. I add some thyme, a bayleaf or 2, and peppercorns. I also add in some celery, parsley, a carrot and an onion. Some fresh lovage would be great as well, but that's pretty obscure...but delicious. Cover all that with water and boil. Yeah, it's going to smell like a lake in your house. That smell will go away after a while and it will smell great. After an hour or two, I strain it though a fine strainer. Throw out everything else. Yes, even the veggies. If you try and eat them, they don't taste like anything after making a stock.
Now comes the goodness. I'll take a little pork fat...bacon, salt pork (my favorite), panchetta, it doesn't matter. I'll render a little of that down and add in some onion and celery. I'll sweat those down. Then I add in a bunch of potatoes diced finely...like 1/2 inch, and the broth. Cook that down until the potatoes are done. Stir in some fish fillets and let it steep for a bit. If you're using bluegill, they're pretty much done after a minute, but if you have huge chunks I'll wait. I usually turn it off when I add the fish. Sometimes I'll also add in a little chopped or dried tarragon. Not much, you can overdo it easily. I always salt things when I eat them. The broth won't taste like anything until you add salt to it. Just add it a little bit by a little bit until it's magical.
I made this when I was visiting my parents last winter. I went out to my dad's pond and caught a bunch of gills. My dad came home as I was boiling it and was completely grossed out by it. I mean grossed out by it! After I finished it, I wanted him to try a bite. He has a very meat and potatoes diet, but knows that if I make something and claim it's good it's probably good. I ended up betting him something and he tried it. He ended up eating the whole batch. I was not happy about it. It's worth the effort. I also like how I don't waste any of the fish outside of a few edible organs.