It Takes Guts to be a Carnivore - Some Thoughts and Recent Developments on Feeds for Aquaculture

The ecological argument goes that feeding carnivorous fish and shrimp (aka “tigers of the sea”) in aquaculture will lead to the depletion of wild forage fish stocks because of the “requirement” for carnivorous fish to eat fishmeal.  What happens when ecological theory meets modern feed ingredients, feed formulation, fish physiology and metabolism?  It turns out that all fish (herbivores, carnivores and everything in between) require the same 40 or so nutrients (Amino acids, fatty acids, vitamins and minerals) and the energy to metabolically utilize them (typically protein and fats).  Modern feed ingredients for fish include protein and lipid concentrates, supplements and flavorings.  The guts of carnivorous fish differ from herbivores in that they have an acid stomach (gastric digestion), while herbivores have no stomach, just a long intestine.  Consequently, carnivores tend to do a better job at digesting diets high in protein and fat than herbivores.  Recent feeding trials with carnivorous fish feed all plant (with or without algae) diets have shown performance equal to those made from fishmeal.  Indeed, as fishmeal prices rise, modern commercial diets for fish and shrimp contain less and less fishmeal and fish oil, being replaced by lower cost alternative proteins and fats