I've spent a lot of time in Maine (40 years ago)
I have three ponds, the biggest is 400' by 100', the smallest 120 x 50.
I'm raising tilapia, catfish, bass, etc. I feed them the floating catfish pellets. The biproduct of this is a lot of nitrogen and phosphate in the water. I've added water lettuce and a floating plant similar to duckweed and water hyanthics (*sp?{. They bind up the minerals as vegetable matter. Then, I harvest about two wheel barrows a day and feed it to the chickens.
As you know, the little buggers are gluttons, so they pig out on the veggies first thing in the morning. After that, I feed them their corn and mash. The plants as I understand are about 8 percent protein, so it's filling and nutritious
Since the fish are used to eating those little pellets, I tie fishing flies out of deer hair, trimmed and dyed to imitate the pellets and fish for them just like you would for trout in a river or lake. They get up to 12 lbs, but the average adult is about 5 pounds. that's about 20 inches and the 12 lb fish is nearly 30 inches in length.
After filleting the fish, I take the carcasses par boil them and feed them to the chickens. At first I was afraid that they might choke on the bones, but in several years of feeding, I've never had it happen.
Also, I've found several plants which grown in my butterfly gardens which overpopulate such as the spanish needles and the birds love them. It cuts my feed bill by 50 percent. I have 140 birds and use slightly over two bags of food per week.
Jack