Reducing the Fish in Fish Feed: Sciences' Rush to Develop Alternative Ingredients

The ecological argument goes that feeding carnivorous fish and shrimp in aquaculture will either limit the expansion of this type of aquaculture or lead to the depletion of wild forage fish stocks because of the requirement for carnivorous fish to eat fishmeal.  However, the nutritional/physiological paradigm is that all fish require more or less the same 40 or so nutrients (Amino acids, fatty acids, vitamins and minerals) and the energy to metabolically utilize them and once consumed, it does not matter where they come from.  Modern feed ingredients for fish include protein and lipid concentrates from plants, animals, and single-celled organisms.  These are mixed with supplements (vitamins and minerals) and flavorings.    It turns out that there are only a couple nutrients that are in short supply and could limit the expansion of aquaculture of marine carnivores, however these molecules can be sustainably produced and supplemented to diets.  In general, 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 better at digesting diets high in protein and fat than herbivores.  Herbivores tend to be able to tolerate carbohydrate better than carnivores.  Recent feeding trials with carnivorous fish fed all plant (with or without algae) diets, with added key nutrients have shown performance equal to those made from fishmeal.  As fishmeal prices have risen, modern commercial diets for fish and shrimp now contain less and less fishmeal and fish oil, being replaced by lower cost proteins and fats.  Recent data shows the use of fish meal and fish oil in aquaculture has decreased while production of the products of carnivorous fish aquaculture has increased.  In addition, the types and supply of key protein and lipid ingredients are undergoing a change due to the use of carbohydrates for ethanol production.  These changes tend to favor production of concentrated protein by-products from the growing bioenergy industry favoring the production of carnivorous fish.  As we move forward, feeds will be evaluated not only for nutritional and economic performance as is done today, but also for environmental and human health performance by taking into account the environmental footprint of feed production and use, and the resulting quality of the product for human consumption.  This “triple bottom line approach”–economics, environment and human health–is supported by 20 specific recommendations and illustrated with seven case studies in a report from NOAA and USDA released last year.  Copies can be obtained at http://aquaculture.noaa.gov.