With all the science behind pond and aquarium hobbies, I'm surprised how difficult it is to find nutrition information about commonly used "feeder fish". I did manage to find some "freeze dried minnows" that are intended as cat/dog treats. The analysis shows 60% crude protein. That is better than I expected and may explain why feeding time in my pond doesn't result in bluegill feeding frenzies. They are surrounded by a higher quality food all day.

https://www.amazon.com/Vital-Essentials-Freeze-Dried-Minnows-Ingredient/dp/B01HC1ZV58


-Jason