This is a simple overview of fish nutrition that gives the basics of what should be in fish feed. 
 
"Fish need energy to maintain basic metabolic activities and to support growth, reproduction, activity, and health. Proteins, carbohydrates, and lipids (the macronutrients) provide this energy and also some essential nutrients. Micronutrients (vitamins and minerals) do not contain calories but are also required for good performance."
 
 
https://freshwater-aquaculture.extension.org/fish-nutrition/