Download New Direction in Fish Feeds and Feeding: Long Term Implications

New Direction in Fish Feeds and Feeding: Long Term Implications
Chhorn Lim
Nutrition Scientist
Aquatic Animal Health Research Unit
USDA-ARS, MSA
P.O. Box 952
Auburn, Alabama 36831
Extended Summary
Aquaculture production of fish and shrimp has expanded rapidly in the past decade and is
predicted to continue to grow steadily for the foreseeable future as the world population
increases and demand for quality seafood continues to rise. Paralleling the growth of the
industry has been the intensification of aquaculture production leading to an increased
use of compound feeds. Successful operation of these production systems is dependent,
among other factors, on the availability of good nutrition (feed and feeding). Since feed
cost represents the major proportion of the overall production cost in intensive
aquaculture, the availability of low-cost, nutritionally balanced diets are critical.
Fish meal, because of its high protein content, amino acid profile closely matches the fish
dietary requirements, high protein and amino acid digestibility, and high palatability, has
been used as the major protein source for most aquaculture species . However, due to the
increased demand, uncertain availability and rising cost of fish meal, considerable
attention has been devoted to progressively substitute fish meal with alternative protein
sources which are less expensive and more readily available. Byproducts of the animal
rendering industry such as meat meal, meat and bone meal, blood meal, are high in
protein and relatively well digested by most fish. Protein quality and palatability of these
products are somewhat inferior to fish meal. Research has demonstrated that these
products and their combination can be used to partially or totally replace fish meal,
depending on fish species. Meat and bone meal is a good source of minerals. Its high ash
content, however, may limit its use in fish feeds due to possible mineral imbalances. It
has been recommended that meat meal, meat and bone meal and blood meal or their
mixture may be used at a level of 5 to 10% in fish feeds, provided that feeds contain
adequate levels of essential amino acids. Because of bovine spongiform encephalopathy
or “mad cow disease”, these products are banned in animal or fish feeds in EU countries
and are generally avoided in aquaculture feeds in countries that export aquaculture
products to EU countries. Some fish feed manufacturers in the U.S. have voluntarily
discontinued the use of meat and bone meal as a precautionary measure. Poultry
byproduct meal has also been used successfully as partial or total replacement of fish
meal, depending on the species. On an equal protein basis, poultry byproduct meal can
substitute 35 to 70% of fish meal in diets of most aquaculture species. The nutritional
value of feather meal is poorer than that of poultry byproduct meal. Many plant protein
ingredients have been used in domestic animal feeds but relatively few are used in fish
feeds because fish have high dietary protein requirements (25 to 45%). Consequently,
only high protein content plant feedstuffs are used in fish feeds. Oil seed byproducts such
as soybean meal, rapeseed meal and cottonseed meal, because of their availability and
low cost, are the most promising alternative protein sources for fish feeds. Compared to
fish meal, these plant ingredients are commonly deficient in lysine and methionine, and
contain indigestible carbohydrates, phytin, tannin, allergens and antinutritional
factors/toxins such as trypsin inhibitors in soybean meal, glucosinolates in rapeseed meal
and gossypol in cottonseed meal. Various soybean products have been used successfully
as substitutes for 25 to 80% fish meal in fish diets, depending on the species and type of
product. Salmonids and carnivorous fish tolerate lower dietary levels of soybean products
than omnivorous or herbivorous fish. Higher levels of fish meal can be substituted if soy
protein concentrate is used. Acceptable inclusion levels of rapeseed/canola (low erucic
acid and glucosinolates rapeseed) meal range from 10 to 25% depending on the species
and age of the fish, and the glucosinolate content of the meal. The amount of cottonseed
meal that can be included in fish diets depend primarily on the levels of free gossypol and
available lysine. Because free gossypol is bound to lysine during processing of
cottonseed into meal, lysine availability decreases as free gossypol decreases. Available
data indicate that, depending on the species, solvent extracted cottonseed meal can be
incorporated in fish diets at levels of 10 to 30%. Numerous studies have shown,
however, that high levels of these plant ingredients usually resulted in poor performance
due mainly to reduced feed consumption, deficiency of essential amino acids and energy,
and presence of anti-nutritional factors, toxins and indigestible components such phytin
and non-starch polysaccharides. Supplementation of deficient amino acids with
crystalline amino acids has shown to improve the nutritional values of these plant feed
stuffs. Dietary addition of exogenous enzyme, phytase, has been shown to increase the
phytin phosphorus availability to numerous fish species. Feed consumption can also be
improved by dietary addition of palatability enhancers such as fish hydrolysates, fish oil
and certain amino acids such as glycine. It is expected that the percentages of fish meal
used in future fish feeds will decrease and higher percentages of alternative protein
sources will be used. This created several problems such as balancing the essential amino
acid content in the diets, increasing the nutrient retention/availability, eliminating
counteracting the physiological effects of antinutritional factors and improving the diet
palatability. This is particularly important when high levels of plant ptotein ingredients
are used. However, in certain regions of the world where alternative protein sources are
expensive relative to the price of fish meal, aquaculture diets still contain substantial
amount of fish meal.
The benefit of using good quality feed can only be realized if fish are properly fed. For
maximum growth, farmers are interested in high rates of feed consumption. However,
uneaten or excess feed cannot be recovered and represent not only an economic loss, but
also deteriorate water quality. Thus, for fish farming to be profitable and sustainable,
good feeding practices (feed allowance, feeding method, feeding frequency and daily
feeding schedule) must be applied. However, because numerous factors such as culture
system and intensity, fish species and size, water quality variables, feed palatability and
quality influence fish feeding, feeding strategies for several fish species have not been
worked out.