Aquaculture is continuing a global trend set in the last decade to be one of the most rapidly expanding businesses in the food production sector. Fish and shrimp production methods are also intensifying, requiring increasing amounts of more precisely formulated feeds. However, there are two very important issues in aquaculture nutrition that need to be addressed for aquaculture to continue as a sustainable industry; first, the development of alternative protein and lipid ingredients to the declining industrial fishery derived sources, and second, formulations that reduce nitrogen and phosphorus discharge to the aquatic environment. Several reviews have addressed alternative protein and energy sources to fishmeal and fish oil where rendered animal products, seafood processing by-products, grains and oilseeds have been assessed for use in aquaculture feeds. Although soybean meal is widely used in aquaculture its inclusion is limited by the presence of antinutritional factors, sulphur containing amino acid deficiency and consumer perceptions in certain markets due to its GMO origin.

Recent reports have described grain legumes or pulses, such as field peas as potential ingredients for aquaculture feeds (Burel et al. 1996; Allan, 1998; McCallum et al. 2000; Gouveia and Davies, 2000). Peas offer flexibility to the feed manufacturer as they may replace both energy (e.g. maize corn, wheat) and protein (e.g. soybean meal and fish meal) sources but their use has been limited due to concerns over the presence of antinutritional factors. As a result of plant breeding, several antinutritional factors including tannins and anti-trypsins have been eliminated or substantially reduced in feed peas (Castell et al. 1996). Feed pea varieties of Pisum sativum are a major pulse crop marketed extensively in Europe, Australia and Canada as a source of carbohydrate, mainly starch, and protein for livestock feeds (van Barneveld et al. (2000)). Crop sustainability, availability, development of processing technologies to increase nutrient utilization and the potential for a high dietary inclusion level make pea a choice alternative to traditional ingredients.

The main components of whole feed peas are starch and protein (Table1). Studies reviewed in the following sections generally support the fact that starches are low cost sources of dietary energy that can be well utilized by warm water omnivorous fish and shrimp. In carnivorous fish metabolism of uncooked starch is limited and there are limits to the effectiveness of digestible carbohydrate to spare protein as a source of dietary energy (Gouveia and Davies, 2000). Studies with rainbow trout, reviewed below, have shown that prior heat treatment to gelatinize (Table 1) starch with the objective of improving digestibility was absolutely necessary (Table 2). Diets containing high levels of raw starch are thought to have lower starch digestibility not only because of lowered amylase activity, but also due to an increase in the adsorption of the amylase to the raw starch thus inhibiting starch hydrolysis (Engin and Carter, 2002). The heat and shear imparted by extrusion inflicts damage to the starch granule and renders it much more susceptible to amylase activity, as shown by in vitro digestion and electron microscopy (He et al. 2002b). Thermal processing by extrusion, micronizing (infrared heat) or moist conditioning at 125°C is also positively correlated to digestibility in shrimp (Cruz-Suarez et al. 2001). Tilapia, an example for other herbivorous fish species that secrete copious quantities of amylase digests raw starch well (McCallum et al. 2000). Heat treatment may also have positive benefits apart from starch gelatinisation by decreasing the activity of any heat labile antinutritional factors such as lipoxygenase which can affect the palatability of raw pea products (Thiessen et al. 2003b). Indeed (Cruz-Suarez et al. 2001) found higher intake in shrimp fed micronized pea where the process had not resulted in starch gelatinisation (Table 8).

Dehulling is effective in removing the undigestible fibre component of the seed (10 to 12% of dry matter) with the remaining kernel having a higher energy and protein content (Table 1). Unlike terrestrial species of livestock fish lack the intestinal bacterial flora capable of breaking down significant amount of ingested non-starch polysaccharides. Although cellulase enzyme activity has been found in the intestinal micro flora of channel catfish the amount of cellulose digested can be considered negligible (Stickney and Shumway, 1974 cited by Engin and Carter, 2002). In Atlantic salmon Carter and Hauler (2000) found no correlation between crude protein digestibility and either energy digestibility or dietary α-cellulose suggesting that undigestible carbohydrate did not affect protein digestibility. Similarly, Thiessen et al. 2003 found that while dehulling reduced fibre level (Table 1) neither apparent nutrient, energy nor dry matter digestibility differed between raw whole pea and raw dehulled pea (Table 4) indicating that the fibre level of whole peas was not a concern; in contrast to oilseeds (canola meal, soybean meal) whose fibre compounds are considered as antinutritional compounds. Therefore pea hull fibre is an unwanted dietary bulking agent that results in increased suspended solids of the water, an expense to effluent filtration in intensive recirculated water fish culture systems. However, in certain colored seed coat varieties of pea (Dunn) grown in Australia the hulls contain significant tannin activity where dehulling has resulted in improved protein digestibility (Booth et al. 2001).

¹Nitrogen free extract, calculated by difference.
²Infraready Products Ltd. Saskatoon, SK
³Prestige Protein, Parrheim Foods, Saskatoon, SK.
⁴Propulse 975, Parrheim Foods, Portage, MB.
⁵Starch gelatinisation, mg glucose/g sample released by digestion with amyloglucosidase.

Amino acid composition of feed pea (23% crude protein basis): Arginine 2.31%, Histidine 0.72%, Isoleucine1.10%, Leucine 1.80, Lysine 1.67%, Methionine 0.28, Methionine + Cystine 0.50%, Phenylalanine 0.98%, Phenylalanine + Tyrosine 1.71%, Threonine 0.84%, Tryptophan 0.19%, Valine 1.05%.

Mineral composition of feed pea (% dry basis): Ca 0.07%, P 0.34%, K 0.97%, Mg 0.12%

Fine grinding pea followed by air classification of starch and protein fractions by density provides an economical way to manufacture a higher protein pea product Carter and Hauler (2000). In the process a large fraction of the starch and non-starch polysaccharide is removed. The protein concentration What is it? in pea protein flour (45-55% CP) is comparable to soybean meals but far lower than fish meals (65-75% CP). Wet milling and protein separation by precipitation at adjusted pH, centrifugation and drying of ground pea is used to produce highly concentrated protein fractions similar to the manufacture of other vegetable protein concentrates such as wheat gluten and soybean protein concentrate. Pea proteins produced by dry and wet milling are highly digestible in fish particularly in salmonid species (Allan, 1998; Carter and Hauler (2000); Thiessen et al. 2003).

Nutrient and energy requirements differ for different species of fish and shellfish. Warm water fish eg. carp, catfish and tilapia tend to be omnivorous and their natural diet includes vegetable foods. Cold water and marine species like the salmonids and European seabass are carnivorous and use protein and lipids as energy sources with limited ability to metabolize carbohydrate. The nutrient requirements have been reported for several farmed fish species, and nutrient requirements determination remains an ongoing field of investigation. This is of particular importance to replacing fishmeal with vegetable ingredients in current fish feed formulations, because fishmeal not only provides amino acids in a desirable pattern but also contains essential lipids, minerals and palatability factors (Thiessen et al. 2003b), whose requirements are not known. Feeds for aquaculture are generally formulated on a digestible energy and nutrient basis. The fact that fish have an equivalent body temperature to their aquatic environment and that they excrete nitrogen mostly as ammonia instead of urea suggests that determination of metabolizable or net energy is not necessary, as in terrestrial species.

The first step in evaluating an ingredient for a particular species is the determination of digestibility for key nutrients and energy. The general method for the determination of apparent digestibility coefficients (ADC, %) involves collection of feces from fish fed diets containing an indigestible indicator, usually 1% chromic oxide or insoluble ash. A settling column is used to separate feces from the effluent water (Gomez et al. 1995; Engin and Carter, 2002). For determinations with shrimp where the fecal matter is very small a siphon method is used to collect feces (Cruz-Suarez et al. 2001. A reference diet is prepared along with diets containing 70% of the reference diet plus 30% of the test ingredients. These diets are fed to separate groups of fish and feces are collected for several days, then rinsed dried and analyzed for nutrient and marker concentration. The apparent digestibility values of the diets are calculated and by difference the ADC for nutrients and energy.

The effects of processing samples of Canadian pea from the same composite lot on dry matter, crude protein and starch digestibility shows expected differences between shrimp, tilapia and rainbow trout (Table 2). Similarly Australian studies have evaluated the effects of processing feed pulses on digestibility (Table 7).

¹Prestige Protein, Parrheim Foods, Saskatoon, SK.

Generally nutrition experiments begin with the hypothesis that when alternate ingredients are used in diets containing the same concentration of digestible energy, digestible protein and meeting nutrient requirements, similar performance can be expected. However, Gomes et al. (1995), for example, found that although feed conversion was not altered voluntary food intake in trout fed diets containing coextruded peas and canola was depressed, due to inherent factors present in plant ingredients, and similar growth was not obtained. Therefore, following the determination of ADC's a feeding trial is conducted with diets containing increasing levels of inclusion of the test ingredient, or at a single dietary concentration where the ingredient has been subjected to different processing treatments, to observe the effects on feed intake, growth, conversion and other parameters of interest. Based on these results inclusion limits can be expressed for an ingredient in the diet of a particular species.

The use of highly digestible ingredients in balanced aquaculture feeds reduces nutrient and solids discharge to the aquatic environment. In aquaculture feed manufacturing great emphasis is placed on pellet integrity to avoid waste. In particular shrimp feed slowly off the pond bottom and therefore feed pellets are assessed for nutrient leaching. In this regard Cruz-Suarez et al. 2001 and Bautista-Teruel et al. (2003) reported percent recovery of dry matter and crude protein following submersion in seawater to be acceptable in shrimp feeds containing pea meals. The lowest loss was found with extruded pea (Cruz-Suarez et al. 2001).

Salmonids include the popular farmed species of salmon, char and trout. These are carnivorous fish that have a limited ability to metabolize raw starch. After their juvenile fresh water phase trout can be raised in either fresh or marine water. Rainbow trout are a popular food fish cultured around the world and also serve as common species for nutritional experimentation.

An early study in France by Kaushik et al. 1993 demonstrated the potential of pea in trout feeds. Apparent digestibility of pea starch improved from almost nil to 96% following dehulling and extrusion. Using values of 23% for digestible protein content and 13.3kJ/gDM for digestible energy Kaushik et al. 1993 then conducted a growth trial where extruded peas were included in diets at 0, 15 and 25% replacing extruded corn and wheat and a portion of fishmeal, in a lower cost formulation and compared to a commercial feed (Table 3).

In the same row, means with no common letter are significantly different (P<0.05).

The results demonstrated that previously reported constraints on the use of pea due to antinutritional factors and poor digestibility could be overcome by processing treatments. Further to the performance results, this trial showed that phosphorus discharge could be halved compared to a commercial feed with a diet incorporating peas (Table 3).

In order to overcome the constraint of a sulphur amino acid deficiency that would limit the amount of pea that could be incorporated in trout diets, Gomez et al. 1993 fed four experimental diets containing graded levels of colzapro (Adour Agriculture Cooperative, France), a co-extruded product of whole rapeseed and peas (50:50), to partially replace fishmeal. The results showed no negative effects on growth, nitrogen or energy utilization from including colzapro at a dietary concentration of 24%. These authors then determined the ADC's of colzapro (DM 90%, CP 94.5%, kJ 87%) to be amongst the highest of several ingredients tested in rainbow trout (Gomez et al. 1995).

Burel et al. 1996 evaluated extruded whole pea, extruded whole lupin and canola meal in trout diets in France. At 30% dietary inclusion both the pea and lupin diets provided growth and conversion equivalent to the all fishmeal protein control diet and superior to canola at 30% inclusion. However due to its higher protein concentration lupin also proved satisfactory at 50% dietary inclusion. Burel et al. 2000 reported ADC's of 66, 88, 69, 83 and 43% for dry matter, crude protein, energy, starch and phosphorus respectively for extruded whole pea in trout. These values were similar to those measured for rapeseed meal and extruded lupin meal except for a lower energy digestibility which the authors attribute to incomplete gelatinisation of pea starch.

A recent study conducted in Saskatchewan to evaluate the effects of milling processes and heat treatment of pea (see Table 1), showed differences in ADC's for dry matter, energy, starch, ether extract and crude protein (Table 4, Thiessen et al. 2003,). Individual amino acid digestibility values were similar and did not show the same statistically significant differences as were observed with crude protein.

In the same row, means with no common letter are significantly different (P<0.05).

Dehulled pea and air classified pea protein were then evaluated in extruded trout diets at a 25 and 20% inclusion respectively replacing soybean meal in a practical formulation. The 12 week trial showed no significant differences in performance amongst treatments (Thiessen et al. 2003,). These authors also conducted a short term palatability trial and a 12 week growth experiment to evaluate thin distillers' solubles as a palatability enhancer for feeds containing 30% pea protein flour. While a short term feeding response was noted, over the long term no differences were observed in feed intake and growth leading these authors to confirm that palatability was not a constraint to the use of pea protein flour in extruded trout feeds (Thiessen et al. 2003b).

He et al. 2002 conducted feeding and digestibility trial with juvenile coho salmon, to determine the nutritional value of differently processed Canadian pea ingredients (Table 1) as partial or total replacement of fishmeal protein, and to demonstrate how the ingredients with different protein

concentrations would be applied to practical diets. Eight isonitrogenous and isolipidic diets were formulated containing 48% crude protein and 19% lipid where protein supplied by fishmeal (steam dried herring meal, 73% CP dry basis) in the reference diet (1) was replaced with the respective pea products (Table 5). All diets contained 7% spray dried krill hydrolysate to enhance food intake.

The results from their study showed that micronized pea and dehulled extruded pea respectively could replace all the wheat and 7% of fishmeal protein (diets 2 and 3, Table 6), the limiting factor to dietary inclusion being the protein concentration in whole pea.

The most significant finding of this study was the potential for pea fractionation by air classification and furthermore for a pea protein concentrate PPC prepared by triple washing PPF with 50% aqueous ethanol. By replacing 25% of fishmeal protein with PPF and PPC respectively (diets 4 and 5) similar growth and performance was also obtained. The 68% crude protein concentration of PPC allowed for its incremental inclusion replacing 25, 50, 75 and 100% of fishmeal protein (Table 5). Diets 4-8 were supplemented with L-methionine and diets 6-8 with calcium phosphate to meet published requirements. After six weeks trial no significant differences were observed among the dietary treatments. However, feed intake was higher for and concomitantly the feed gain ratio increased for coho salmon receiving diets with higher PPC amounts. This was accounted for by a significantly lower ADC for energy in the PPC diets due to lower digestibility of the dietary lipid source; and that fishmeal replacement did not impair voluntary food intake due to palatability as fish ate to meet energy requirements (Table 6). Apparent crude protein digestibility of the diets increased as pea protein replaced fishmeal in the series of diets.

In the same row, means with no common letter are significantly different (P<0.05).
¹SEM= standard error of the mean.
²IBW =initial body weight (g/per fish).
³FBW =final body weight (g/per fish).
⁴FI= Feed intake (g/kg/d).
⁵FGR (Feed gain ratio) = dry matter intake/wet weight gain.
⁶PER (protein efficiency ratio)= wet weight gain/protein intake.
⁷Apparent digestibility coefficient % (ADC) for crude protein.
⁸ADC % for gross energy.
⁹ADC % for starch.
¹⁰ADC % for phosphorus.

An Australian study (Carter and Hauler, 2000 also evaluated air classified pea protein using the Dunn pea (Pisum sativum) cultivar. In comparison to air classified protein from narrow leafed lupin, the pea protein and soybean meal showed the best potential in terms of growth, feed conversion and ADC's for dry matter, crude protein and energy. This study showed that pea protein could replace at least 33% of fishmeal (27.5% of the diet) in extruded feeds for to juvenile Atlantic salmon.

Burel et al. 2000 reported ADC's for extruded whole pea included at 30% in diets fed to turbot a species cultured in Europe, of 72, 93, 78, and 75% for dry matter, crude protein, energy and starch respectively. These authors noted that removal of the hull and complete starch gelatinization would likely have resulted in higher values as was the case with two rapeseed meals, one of which was extruded.

Tilapia are a tropical omnivorous group of food fish that includes various cultured species. Manufactured feeds for intensive culture usually contain fish meal or other animal derived proteins and large amounts of plant ingredients. Dry matter and protein digestibility were improved as a result of hull removal but not from the heat treatment. ADC's for starch in Nile tilapia (Oreochromis niloticus) were high and showed no effects from dehulling or extrusion (Table 1). Fontainhes-Fernandes et al. 1999 also obtained high digestibility values of 85.5, 93 and 89% for dry matter, crude protein and gross energy respectively with a dehulled extruded pea meal (Aquatex®, Sotexpro, Reims, France). In subsequent growth trials dehulled raw and extruded pea meals were shown to be acceptable ingredients for tilapia (Fontainhes-Fernandes et al. 1999, McCallum et al. 2000.

Allan et al 2000 reported a comprehensive study to determine the ADC's for dry matter, nitrogen, energy and individual amino acids for commonly used ingredients for silver perch, a native Australian freshwater omnivorous species. The test ingredients included fishmeal, animal meals, oilseed meal, cereals and whole legume seeds. The latter included lupins (L. angustifolius and L. albus), field pea (Dunn), faba bean (fjord), chick pea (desi), vetch and cow peas. Silver perch were capable of digesting dry matter, protein and energy effectively from the pulses except vetch, known for a high content of antinutritional factors. However compounding the relatively low concentration of sulphur containing amino acids in legume seeds were lower ADC's for methionine and cysteine, 68% and 61% respectively for Dunn field pea. Booth et al. 2001 reported higher apparent digestibility coefficients for dry matter and energy for dehulled peas compared to whole peas and in turn air classified pea protein, and a similar trend was noted for other Australian pulse seeds (Table 7).

Stone et al. 2003 found that silver perch were able to digest and utilize dextrin, pregelatinzed wheat starch, and raw wheat starch better than raw pea starch in that order. The authors attributed the differences in digestibility of the raw starches to the higher amylopectin content of wheat starch. Booth and Allan 2003 employed a comparative slaughter and growth assay to evaluate different inclusion rates of dehulled pea and reported that up to 60% replacement of a fishmeal, soybean meal, wheat and sorghum based diet could support satisfactory growth in silver perch.

¹ By definition protein concentrates contain more than 65%CP therefore the term protein flour is used in Table 1 to describe a similar product.

The Australian short-finned eel is considered to be a prime candidate for inland aquaculture. Commercial feeds contain high levels of high quality fishmeal suggesting that it is a highly carnivorous species. The ADC's for dry matter, crude protein and energy for ground whole field peas autoclaved at 105°C for 10 min. were 37%, 85% and 46% respectively (Engin and Carter 2002. The dry matter and energy ADC were lower than for soybean meal, maize gluten meal, canola meal, lupin meal and animal derived meals. The ADC for crude protein was similar to that of soybean meal and poultry meal but lower than the other ingredients. It is possible that the heat treatment was insufficient to enhance digestibility of pea by Australian eel.

Gouveia and Davies, 1998carried out a preliminary evaluation of pea seed meal in diets for European sea bass, a farmed marine fish of high economic importance in Mediterranean Europe. The pea seed meal was prepared from whole pea by dry cooking at 180°C for 30 minutes and grinding through a 1mm. screen with a hammer mill. In an 84 day feeding trial these authors demonstrated that up to 40% pea seed meal inclusion (the maximum level tested) could replace 12% of fish meal without impairment to growth performance or nutrient utilization as measured by feed conversion and nitrogen deposition. ADC's of the diets at the end of the growth trial showed high digestibility for protein and lipid, 89% and 92% respectively for all diets Carbohydrate and hence dry matter and energy digestibility, and carcass lipid deposition was reduced as dietary pea meal inclusion was increased.

The above pea seed meal was not typical for a commercial product therefore these authors followed with a 11 week growth trial with groups of juvenile European sea bass fed diets containing 0, 10, 20 and 30% of a commercial pea seed meal (Aquatex®, Sotexpro, Reims, France), which according to manufacturers is a dehulled, defibered, destructured, cooked, sterilized and micro ground product (Gouveia and Davies, 2000). In this study ADC's of all nutritional components remained high in the diets and there was no indication of negative effects in the growth trial. Therefore extrusion cooking appears to gelatinize starch and render it digestible by the fish. Subsequently, Russel et al. 2001 showed that as extruded pea seed meal content was increased in sea bass diets there was an increase in lipid and glycogen deposition in the liver. This is consistent with a higher digestible carbohydrate intake and the inherent inability of carnivorous fish species to mobilize carbohydrate as an energy source.

Gilthead sea bream is also a Mediterranean species of economic importance. Pereira and Oliva-Teles 2002 evaluated two pea seed meals, one dehulled and extruded (Aquatex®, Sotexpro, Reims, France) and one whole pea treated by infrared radiation and ground. The meals were included in isocaloric diets containing 44% crude protein replacing 10 and 20% of protein provided by fishmeal. At the end of the experimental period there were no differences in growth, feed conversion, fish proximate composition and protein retention between the experimental diets and the control diet, where all of the protein was supplied by fishmeal. These authors also observed lower dry matter and energy ADC's particularly in whole pea meal indicating indigestibility of the hull fibre.

Legume seed proteins including soybean and pea are known to be deficient in sulphur containing amino acids for aquaculture species and terrestrial animals. Therefore Schwarz et al. 1998 used ground pea as the main ingredient in a basal diet used to determine the methionine requirement of common carp. This study demonstrated that ground peas are an acceptable ingredient for carp provided a source of methionine is included.

Milkfish is a tropical marine fish species that has been cultured in the Philippines for many years under semi-intensive nutritional management employing organic fertilizers and fodders. The current trend is towards the use of manufactured feeds requiring the evaluation of various protein sources. Borlongan et al. 2003 reported that milkfish fed diets containing up to 26% unprocessed feed pea inclusion showed better growth rates and feed conversion than commercial feed control groups. However, an amino acid deficiency was suggested as the reason for depressed growth performance where pea flour replaced soybean meal and wheat flour in experimental diets above 15% inclusion.

An interesting low cost pea (Pisum sativun) containing cattle fodder feed used in India called Chuni (22% crude protein) was fed to rohu in four experimental diets incorporating this feedstuff at levels of 10, 20, 30, and 40% in a fishmeal, mustard cake and rice bran based control diet containing 35% protein (Saha and Ray 1998). However the proportion of pea was only 5% in this cereal and legume seed Chuni and fish growth, diet digestibility and feed conversion were compromised at inclusion levels above 10%. The authors attribute the decreased performance above 10% inclusion to a decrease in digestive protease and α-amylase activity due to anti-nutritive factors in Chuni.

Smith D. M. (unpublished) cited by Allan 1998 reported ADC's of 72, 83, and 89% for dry matter, energy and protein from whole pea in tiger shrimp. Similar high values of 73 and 93% for dry matter and protein digestibility were recently reported by Bautista-Teruel et al. (2003). Digestibility of the feed increased with increasing ground pea concentration in a series of feeds where pea meal replaced defatted soybean meal, to supply from 0 to 25% of total dietary protein in 5% increments. In a 90 day growth study no significant differences in feed intake, weight gain, feed conversion, protein efficiency ratio and whole body proximate composition at the end of the trial were noted among shrimp fed these diets. Pellet water stability was similar for all levels of feed pea replacement. This study clearly demonstrated that ground whole pea at 42% inclusion can satisfactorily replace soybean meal and meet amino requirements of tiger shrimp.

Canadian pea subjected to different processes were evaluated in diets for blue shrimp (Litopenaeus stylirostris) and white shrimp (Litopenaeus vannamei) by Cruz-Suarez et al. 2001 and Davis et al. 2002 respectively. Dry peas of mixed Canadian prairie varieties were processed to prepare test pea meals (Table 1). Whole and dehulled peas were pin milled to produce raw flours. Portions of these flours were extruded to produce whole and dehulled extruded meals. Another portion of whole peas was processed using infrared cooking (micronized). The pea meals were tested at a 30% and 25% dietary inclusion for blue shrimp (at U. Autonoma de Nueva Leon, Mexico) and white shrimp (at U. of Texas, Port Aransas, Texas) respectively, in isonitrogenous and isoenergetic diets to replace a portion of soybean meal (46.3% CP) and wheat (12.3% CP) mix (1:4 parts respectively) of a practical control diet.

The two studies found that growth rates of shrimp fed diets containing samples of the differently processed pea meals and the control diet were similar for both species taking into consideration different initial weights. No significant effects were noted as a result of dehulling. Extrusion improved food consumption, growth and feed conversion in L. vannamei. With L. stylirostris, extrusion reduced food intake slightly and improved feed conversion with no effect on growth. The micronized pea diet exhibited the highest food consumption and growth rate with L. stylirostris. These shrimp also showed slightly higher apparent dry matter digestibility coefficients as a result of extrusion effects on starch gelatinisation. Apparent protein digestibility remained high for all pea meals. The results of this study showed that raw peas, and peas processed by dehulling, extruding and micronizing, have a nutritional value in shrimp diets similar to that of a mixture (1:3) of soybean meal and wheat (Cruz-Suarez et al. 2001). The study found that the response to raw whole peas was positive. Therefore shrimp may actually be more tolerant of certain antinutritional seed coat compounds than other species. The lower food consumption of the extruded pea diets did not impair growth and therefore may be explained by the higher energy availability of gelatinized starch resulting from the effects of extrusion cooking The higher dry matter digestibility values would also suggest higher digestible energy value for extruded peas. The gelatinisation of starch by wet extrusion had a small positive effect on digestibility and performance, although the raw pea meal was quite acceptable and perhaps the extrusion costs would not be recovered.

There is now a significant amount of literature concerning pea use in aquaculture diets for species of commercial importance. The potential for pea use as a primary protein source to replace fishmeal clearly requires the use of pea protein concentrates, hydrothermal treatment and sulphur amino acid supplementation. The effects of hydrothermal processing can be realized during feed manufacturing or obtained as a pre-processed ingredient. It was noted by several investigators that carbohydrate is generally not an energy source of choice in compounding aquaculture diets as is the case with terrestrial livestock. Thermal treatment to render starch digestible or removing starches and oligosacharides through milling will undoubtedly lead to more pea use in aquaculture. Whole ground pea may be used in aquafeeds replacing other grains while a concentrated pea protein product would be used to replace protein sources such as fishmeal and oilseed meals for feeds requiring higher protein concentration. Replacing a portion of the fishmeal with pea can reduce the phosphorus discharge to the aquatic environment. A further reduction in phosphorus discharge can be achieved by including a phytase enzyme product in the feed and reducing or eliminating other phosphorus ingredients.

Peas provide excellent feed milling characteristics with a lower incidence of fines in pelletized feeds. The water absorption and gelatinisation of pea flour confers excellent water stability to shrimp feed pellets from nutrient leaching as measured by dry matter and crude protein loss. Ground pea or pea protein meals can be blended with oilseed meals, corn gluten meal or fishery by-products and co-extruded to supplement the sulphur containing amino acid content. Similarly whole flax seed or canola can be co-extruded with pea protein to enhance both protein and lipid quality.

For further information please consult the Pulse-Canola Feed Literature Database at www.infoharvest.ca/pcd