Tuna, salmon, eel, and other carnivorous fish are fed ground-up fish meal. Many think this is an unsustainable practice. Every pound of meat-eating fish requires between two and twenty pounds of fish meal. This continues the drain on our ocean life. Alternatives can and should be looked into.
One protein source is readily available, and currently being used in many areas around the world. Composting earthworms have potential as a substitute. These worms feed on vegetable scraps, wood, and other organic material. In return, they produce a rich compost. Some varieties reproduce at a rate of up to eightfold per year.
Given a large enough worm stock to start with and a steady food supply, worms ought to be a good supplement or possibly an outright substitution for fish meal. Does anyone have experience with this?