Written
by
Ronald.
W. Hardy
Hagerman
Fish Culture Experiment Station, University of Idaho,
3059F
National Fish Hatchery Road, Hagerman, ID 83332, USA
Edited by Fishery
Section of Martins
Library
ABSTRACT:
Aquaculture production has expanded at a
rate of 15% per year and is predicted to continue to grow at this rate for at
least the next decade. Demands on traditional fish feed ingredients, mainly
fish meal and oil, which are finite global resources, are increasing. At present,
global fishmeal production averages 6.5 mmt per year, of which 23% is utilized
in feeds for farmed fish. Global fish oil production averages 1.4 mmt per year,
and 25% of this yearly production is utilized in fish feeds. Up to now, 70% of
the fish meal and
oil used to produce farmed fish has been consumed by salmon, trout and shrimp,
despite the fact that these species account for only 30% of global fish feed
production and only 7% of global aquaculture production.
Clearly, expanded production of carnivorous species requiring high protein,
high-energy feeds will further tax global fish meal and oil supplies. Suitable
alternative feed ingredients will have to been utilized
to provide the essential nutrients and energy needed to fuel the growth of
aquaculture production. Rendered products,
seafood processing waste, including by-catch, and grain and oilseed by-products
are the most likely candidate feed sources to carry aquaculture forward to
higher production levels. Worldwide, annual
production of rendered products is roughly equivalent to annual fish meal
production, with meat and bone meal and poultry by-product meal making up 80%
of total production. These products are variable in quality, high in ash
content, and fully utilized by other agricultural sectors. They are unlikely to
supply a high proportion of the protein needed in fish feeds, but may be
valuable as feed components due to their favorable
amino acid profiles, which complement plant-derived protein sources. If seafood
processing waste and by-catch were converted to fish meal, the quantity would
nearly equal annual global fish meal production
and potentially provide significant fish protein and oil supplies for
aquaculture feeds. However, the high ash content and logistical problems with
collection and processing will limit full utilization of this resource. Grain
and oilseed by-products are thus the most promising sources of protein and
energy for aquaculture feeds of the future.
Despite many successful research studies on the use of plant-derived feed
ingredients in fish feeds, significant problems remain to be resolved.
Innovative collaborative research efforts
between geneticists, fish nutritionists and the industrial sectors producing
these products are beginning to resolve these
technical problems. Use of enzyme supplements is one potential aspect of
alternate ingredient utilization that will increase
the nutritional value and use of alternate feed ingredients.
KEY WORDS: Enzyme supplement, Animal by products, Grain
protein, Oilseed protein.
Hardy,
R.W., 2000. New developments in aquatic feed ingredients, and potential of
enzyme supplements.In: Cruz -Suárez, L.E., Ricque-Marie, D., Tapia-Salazar, M.,
Olvera-Novoa, M.A. y Civera-Cerecedo, R., (Eds.). Avances en Nutrición Acuícola
V.Memorias del V Simposium Internacional de Nutrición Acuícola. 19-22
Noviembre, 2000. Mérida, Yucatán, Mexico.
Martins Library - Nigeria
INTRODUCTION
Fish meal production has averaged
approximately 6.5 million metric tons (mmt) over the past decade, and prospects for this
production to increase are low. The highest annual production of fish meal has
been 7.5 mmt, and the lowest production was between
4.5 and 5.0 mmt, during the 1998 El Niño period, which lowered production of
fish meal from Peru and Chile. Since Peru and Chile have accounted for about 1/3 of global fish meal production, any
change in these countries has a major impact annual production. Further, Peru
and Chile are major fish meal exporting countries, accounting for up to 2/3 of
the amount of fish meal traded throughout the world. Thus, production of fish
meal by Peru and Chile greatly influences the supply of fish meal, which in
turn affects fish meal price (Fig. 1). The price of fish meal is currently
quite low, the result of adequate supplies and relatively low demand, most
likely associated with the economic slowdown in Asia. However, this period of
low fish meal prices is likely to be short-lived, in that economic recovery in
Asia is underway, and production of fish meal in Chile is not expected to recover to pre-El Nino levels in the next few
years (Fig. 2). The aquaculture industry must be prepared for higher feed
costs, associated with higher fish meal costs, and in addition must seek
alternative protein sources to replace a portion of the fish meal in feed
formulations to permit expansion of aquaculture production beyond the level at
which supplies of fish meal become a factor limiting
production of fish feeds, and hence farmed fish.
Fish meal use in aquaculture feeds
The proportion of global fish meal
production that is utilized in fish feeds has increased substantially over the past 10 years. In
1989, aquaculture was a minor consumer of fish meal, using approximately 10% of
annual production (Barlow, 1989). In 2000, fish meal consumption by the
aquaculture industry will be an estimated 35% of total global fish meal production,
an increase 3.5 times in fifteen years. Growth
of the Atlantic salmon and shrimp farming industries has been responsible for
most of the increase in fish meal use by the
aquaculture industry over this period, but the explosive growth of the marine fish farming industry has caused much of the
increase in fish meal use by aquaculture in the last five years (Fig. 3). Feeds
for Atlantic salmon over the past 15 years have contained more than 50% fish
meal, and shrimp feeds 35% fish meal (Barlow, 2000). In the past five years,
these percentages have decreased somewhat, but
nevertheless, feeds for salmon, marine fish, and eels still contain about 40%
fish meal (Barlow, 2000). Predictions of fish meal
needs for aquaculture feeds in 2010 are 2.83 mmt, approximately 44% of the
ten-year average annual global fish meal production of 6.5 mmt. This represents an increase of 716,000 mt over estimates of fish
meal use in 2000. Fish meal use in feeds for carp is predicted to increase by
325,000 mt, and use for marine fish by 447,000 mt, while use in feeds for eels,
salmon, trout, milkfish, and catfish is predicted to decrease (Table 1). Use of
fish meal in shrimp feeds is predicted to
increase from 372,000 mt to 485,000 mt between 2000 and 2010. The percentage of fish meal in feeds for all species groups is
predicted to decrease (Table 2). If the percentage
of fish meal use in fish feeds was to remain the same as today, and aquaculture
production increased to predicted levels in 2010, fish meal needs would be 4086
mmt, or 63% of the average amount produced
over the past decade. The difference between the predicted need for fish meal
by the aquaculture feed industry in 2010 (2.83 mmt), and the amount that would
be needed if the percentage of
219 fish meal in fish feeds did not decrease (4.086 mmt) is
1,255,000 mt. This is the amount of fish meal-equivalent protein sources that
will be needed to replace the ‘missing’ fish meal in fish feeds by the year
2010.
Alternative Protein Sources; Availability
and Quantity
Seafood Processing Waste and By-Catch
Seafood processing waste and fishery
by-catch together exceed in tonnage the global landings of fish for fish meal
production (New, 1996). If half of the fishery by-catch discarded by the
fishing industry each year could be converted into fish meal, this quantity
(2,600,000 mt) could supply the expected needs of the aquaculture feed industry
for the next 15 years or more. Seafood processing waste, which is mainly the
carcass of fish after fillets are removed, contains too much bone to be
producing suitable fish meal for fish feeds. Therefore, the bone content of the
processing waste must be reduced, either before it is made into fish meal by
mechanical de-boning, or after it is made into fish meal by screening (Babbittet al. 1994).Fish processing waste contains ca. 25% ash on a dry
weight basis, but fish meals made from de-boned fish filleting waste can be as
low as 7% ash, half the level of ash in fish meals used in feeds. This is
particularly valuable for the production of low-pollution fish feeds. Expanded
production of low-ash fish meals produced from seafood processing waste is
likely, as is further refinement of the production
process to ensure that the nutritional value of these fish meals remains high.
Rendered products are meat & bone meal
(annual US production 2,819,322 mt) and blood meal (annual US production
101,300 mt). By-products of poultry processing include feed grade poultry
by-product meal
(annual US production 265,910 mt), pet food grade poultry by-product meal
(annual US production 177,270 mt), low-ash pet
food grade (annual US production 24,000 mt), and feather meal (annual US production 363,640 mt). Together, annual US
production of all rendered products plus poultry
processing products totals 3,751,442 mt, or about 50-60% of average annual
world fish meal production. These products are
fully utilized in poultry feeds, pet foods, and other animal feeds. At present their prices are very low in comparison to 10-year
average prices, both on a weight basis and on a protein-unit basis (Table 3).
Rendered products have not been
extensively studied as replacements for fish meal in feeds for carnivorous fish. Dong et
al.((Donget al. 1993)reported that poultry by-product meal varied
considerablyin quality among suppliers, as measured
by apparent protein digestibility. Feeding trials involving poultry by-product meals have demonstrated that
up to 40% of fish meal could be replaced with
pet-food grade poultry by-product without lowering trout growth, but that
higher replacement levels resulted in reduced
growth. Protein digestibility of poultry by-product meal, measured in trout, is
94-95%, equivalent to herring meal (Sugiuraet al. 1998a) but recent
research results suggests that the availability of certain amino acids in
poultry meal is lower than average protein digestibility. Meat and bone meal
and feather meal were considered to be unsuitable for use in salmonid feeds
because early data showed less than 70%
protein digestibility (Cho and Slinger, 1979). Recent re-evaluation of several of these ingredients has shown that earlier work
underestimated the protein digestibility of meat & bone meal and blood
meal, with more recent values showing apparent digestibility coefficients
ranging from 87% to 92% (Hajenet al. 1993; Sugiraet al. 1998b,
Bureau et al. 2000). As is the case with poultry
by-product meal, individual amino acid digestibility coefficients are higher
and lower for specific essential amino acids than the average protein digestibility
value for meat and bone meal (unpublished data,
Sugiura and Hardy, 1998). Initial studies suggest that up to 25% of fish meal
protein can be replaced with meat and bone
meal without compromising growth, but that higher levels of replacement
significantly reduce growth (Schelling and Hardy, unpublished data, 2000). The
nutritional value of rendered products varies
among producers, and even among manufacturing plants owned by the same company. The most important determinate of nutritional
value is the source and freshness of the raw material
used to produce the meals. At present, rendered products are sold at commodity
prices, but efforts are being made within the
rendering industry to range products and establish grades corresponding to nutritional value.
Grain Proteins
Wheat gluten is an excellent protein
source, containing 70-80% protein that is highly digestible to rainbow trout, coho salmon
and presumably other fish species (Sugiura et al. 1998). Up to 25% of
fish meal has been replaced with wheat gluten without negative effects on
growth or feed conversion ratios (Weede, 1997). Higher replacement levels
combined with lysine supplementation are reported to support trout performance equivalent to fish meal-based
diets (Rodehutscordet al. 1994). The main drawback of wheat gluten is its relatively high price. Wheat gluten is
currently produced for human consumption as a
high-value, non-meat protein source. If lower quality, cheaper, feed-grade
wheat gluten were developed, this ingredient
could become an important aquaculture feed ingredient.
Corn gluten is an excellent protein
source, containing a minimum of 60% protein (Moraleset al., 1994) which is 97% digestible to
trout (Sugiura et al. 1998). Corn gluten can substitute for 25–40 % of
fish meal without negative effects on growth or feed conversion ratios in trout
(Morales et al., 1994; Weede, 1997). The main disadvantage of corn gluten for
commercial trout diets is that it imparts a yellow color to fish flesh when
included at a high proportion of the diet (Weede, 1997). Nevertheless, it is a
valuable ingredient when included at levels up to 10% in trout diets, and, when
trout or salmon are raised with the intention of producing fish with pink
colored flesh, corn gluten can be included as up to at least 22.5% of the diet, along with canthaxanthin or astaxanthin,
which masks the yellow color in fillets (Skonberget
al. 1998). For fish species that do not deposit carotenoid pigments in
their flesh, corn gluten can be used at even
higher dietary levels. Corn gluten has the advantage of being plentiful and low
priced. In 1997, U.S. production alone amounted to 1.178 mmt, and was priced at
$380 per mt. Currently, corn gluten produced
from white corn is being evaluated as a feed ingredient for salmonids, and
initial results appear promising (Hardy, unpublished data, 2000). White corn
gluten meal will likely be priced at a premium to regular (yellow) corn gluten
meal, but protein levels are at least 10% higher, which justifies the increased
cost.
Oilseed Proteins
Soybeans, as other plant-derived protein
sources, have several antinutritional factors (ANFs), which can reduce
palatability, protein utilization or growth (Hardy, 1996). These can be divided
into two categories:
heat-labile and heat-stable ANFs (Rumseyet al. 1995).Heat-labile ANFs
include trypsin inhibitors, phytates,
lectins, goitrogens and antivitamins. Heat-stable ANFs include
carbohydrate or soluble fiber, saponins,
estrogens, allergins, and lysinoalanine. Heat-labile constituents can be at
least partially degraded by heat treatments,
so the effects of these antinutritional factors reduced by adjusting the heat
treatment used during soybean presscake drying (Vohra and Kratzer, 1991).
Trypsin inhibitors decrease the activity of trypsin, a digestive enzyme that
breaks down proteins in the intestine. Trypsin inhibitors lower protein
digestibility in diets for salmon and trout (Arndtet al., 1999).Phytate
or phytic acid has been reported to reduce protein digestibility and limit the
bioavailability of minerals (Spinelliet al. 1983; Riche and
Brown, 1996). Much of the phosphorus in plant-derived ingredients is bound in
phytate. Supplementing the diet with the enzyme
phytase can break down a portion of the phytate, increasing availability of dietary phytate-phosphorus in diets for fish
(Rodehutscord and Pfeffer, 1995; Schaferet al., 1995; Cain and Garling,
1995). Soybean lectins have been shown in vitro to bind to the brush
border membrane of Atlantic salmon small intestine (van den Ingh et al.
1991), but no studies have been conducted on
performance or health effects of lectins on fish. The carbohydrate fraction of
a soybean is approximately 30% of its dry weight, and only 33% consists of the
soluble fraction (oligosaccharides, raffinose,
sucrose, and stachyose), or the fraction available for energy use (Arnesenet
al. 1989).
Arnesen et al. (1989) suggested that a large fraction of the potential
carbohydrate energy is not available to salmonids because most of the soybean
polysaccharides cannot be absorbed. This carbohydrate
fraction is unavailable because salmonids only have the enzyme necessary to
digest starch and starch makes up less than 1% of soybean meal. A crude saponin
extract of soybean meal was found to lower feed intake of chinook salmon fingerlings
and to reduce growth of rainbow trout (Bureauet al. 1996). Overall, there are several ANFs that could influence
the nutritional value of soybean meal and other plant-derived ingredients for
fish; additional processing or diet supplementation may be required to realize
the full nutritional potential when these ingredients are used in fish feeds.
Soybean productsare generally high in
protein, ranging from about 45% protein for soybean meal to over 70% protein for soy
protein concentrate. Soybeans are the most plentiful of oilseed crops, with a
worldwide production of 132.53 mmt in 1996. US production of soybean meal in
1996 was 30.6 mmt, and the price was $289 per mt. Soy protein concentrate is
produced in smaller quantities, with US annual
production of 85,000 mt, and is priced at about $990 per mt. Early studies with
soybean meal in trout feeds showed that trout tolerated relatively high levels
of soybean meal in their feeds, especially if the meal was heat-treated to
inactivate trypsin inhibitor levels (Choet al. 1974; Reinitz, 1980).
Studies with Pacific salmon fingerlings, however, are less promising, with some
studies showing that feed intake was reduced even at 5% soybean meal in the
diet (Higgset al. 1979; Fowler, 1980). Recent studies with post-juvenile
Pacific salmon have been more encouraging, suggesting that larger fish are more
tolerant of soybean meal in their feed than are fry and fingerlings. Wilson
(1992) found that full-fat soybean meal,
heat-treated by double extrusion to lower trypsin inhibitor levels, could be
used in diets for post-juvenile chinook salmon at levels up to 15% of the diet
without reducing growth rates or feed efficiency ratios, but that diets
containing more than 15% full-fat soybean meal resulted in reduced feed intake and
growth. Further research is necessary to determine whether higher levels of
soybean meal can be included in diets for
salmon when appetite stimulants are included in the diet, and to determine the
relative importance of various antinutritional
factors in soybean meal for fish. In contrast to salmon and trout feeds,
catfish feeds depend heavily on soybean meal to provide dietary protein.
Current catfish feed formulations in the US
contain 45-50% soybean meal, with less than 10% fish meal (Wilson, 1991). Similarly,
tilapia and carp feeds generally contain less than 15% fish meal, with soybean
meal or other alternate protein sources providing the bulk of dietary protein
(Luquet, 1991)(Satoh, 1991).
Other By-Product Proteins
By-products of the brewing and distilling
industries are widely available and underutilized in feeds for fish. Rumsey et al.(1991)found
that the protein quality of Saccharomyces yeast (brewers or bakers
yeast) in diets for rainbow trout is improved by a
treatment to disrupt the cell walls, thereby making the protein more available.
When yeast cell walls are disrupted, 50% of the protein in rainbow trout diets
can be supplied by bakers yeast with equivalent growth and feed conversion
ratio to a control diet with protein supplied by casein and gelatin. Although
single cell proteins are potentially good protein sources, limited availability or high cost has so far
limited their use in fish diets. This situation may change in the near future, however, as new processes are
developed to recover single cell proteins from brewery waste, and upgrade its
quality by air-classification to lower fiber content.
Role of Enzyme Supplements
As fish meal is increasingly replaced in
fish feeds with non-traditional protein sources, the opportunity to improve the
nutritional value of these protein sources by enzyme supplementation will
increase. Phytase is already used in swine and poultry feeds to increase
phosphorus availability in grains and oilseeds by dephosphorylation of myo-inositol
hexakisphosphate (phytate))(Cromwellet al. 1993). Studies with catfish (Jacksonet al. 1996; Eya and Lovell, 1997;
Li and Robinson, 1997) and trout (Cain and Garling, 1995;Rodehutscord and
Pfeffer, 1995; Vielmaet al. 2000) demonstrate the effectiveness of
phytase at increasing phosphorus availability in fish, although these studies
also demonstrate the significance of rearing
water temperature on effectiveness and optimum dietary phytase level. Li and
Robinson (1997) found that the cost of adding phytase to catfish feeds was
nearly equal to the savings associated with eliminating
dietary supplementation with inorganic phosphorus.
Other enzyme supplements are not widely
used, but may be added to future fish feeds to increase nutritional value when
alternate ingredients are included. For example, mixtures of proteases may be
used increase the digestibility of protein in
rendered products. Such products would contain enzymes that hydrolyze connective tissue and skin, two components
of rendered products that are difficult for fish to digest. Another category of
enzyme supplements is those that break down fiber and certain carbohydrates found in protein sources from grains and
oilseeds. One such product, designed specifically for use in high-wheat feeds
for poultry, contains endo-xylanase, which breaks down pentose sugars. A
similar product breaks down glucans found in wheat, barley, triticale and rye,
releasing glucose. To date, these products
have been only used in poultry and swine diets, but it is likely that they will
be effective in diets for tilapia, catfish,
and perhaps shrimp.
Specific enzyme supplements are needed to
overcome various components of the carbohydrate fraction of oilseeds. As
mentioned above, soybean non-starch polysaccharides are suspected of being one
of the problems that limits soybean meal nutritional value for some species of
fish. Studies in poultry show that supplementing feeds with a glycanase increases
the performance of the birds when their diet contained low metabolizable energy
wheat (Choct, Hughes, et al. 1995 #20771). Supplementation with the enzyme significantly
increased solubilization of non-starch polysaccharides in the intestine of the
birds. Enzymes that break down non-starch
polysaccharides must be tested in fish to determine if nutritional value, specifically energy availability, is increased in
soybean meal-containing diets when enzyme supplements
are used.
SUMMARY
Expanded aquaculture production will
require more fish feed, which will in turn require higher quantities of
alternate protein sources to substitute for fish meal. An estimated 1.5 mmt of
alternate proteins will be needed just in the next decade to supply global
needs. If fish meal supplies decrease, higher amounts will be needed. Most
likely, these proteins will be supplied from a variety of sources, most of
which requiring
special processing or enzyme supplementation to realize their full nutritional
value. The aquaculture industry should look to
blends of protein sources from plant sources and from animal or fish sources.
Such blends would more closely approximate the excellent amino acid profile of
fish meal that any single protein source, with the exception of fish meal produced
from seafood processing waste.
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