Your comments are very valid in terms of using fish meal for fish production and the fact that fish are more efficient protein converters than terrestrial land animals.

However, while these other species are less efficient from a kg of protein fed to kg of protein gained perspective, there is the factor of economic efficiency. Historically, land animals are a lot cheaper to produce on a kg basis than fish through aquaculture. In the end, if you are purley comparing protein production, and not omega 3’s or other nutritional substances, then aquaculture still struggles to compete from a price perspective. Therefore, resources such as feed ingredients, tend to flow to those industries that are more efficient, economically.

However, to help alleviate the fish meal situation there is a lot of work going on on utilising wastes from land animal processing for fish production. However, this too is questionable to some.

The solution may be to use land animal bi-products (blood meal, meat and bone meal, etc.) to produce microbial protein with the right balance of amino acids to suit certain animal and fish nutritional profiles. What this space as there is a fair bit of work going on in this area right now. I know of some people in Asia working very hard on this at present and the early results look very exciting.

Regards,
Dale