Feed Peas in diets for shrimp tilapia and milkfish - Northern Pulse ...

of competing protein sources. The digestibility of the peas is also considered in evaluating its potential as aprotein source. In the present study, the digestibility coefficients for feed peas in Nile tilapia are comparableto those reported for other freshwater fishes (Table 8). The highest digestibility coefficients for P. sativumwere obtained in turbot, a marine species. In a companion study, the crude protein digestibility of feed peasin milkfish was also higher (92%) than in tilapia; however, dry matter digestibility was lower (I. Borlongan,personal communication 2002). Allan et al. (2000) determined the digestibility of peas and other ingredientsin silver perch as well as that of amino acids in the ingredients. The protein digestibility of the ingredientswas a reflection of the availability of amino acids in silver perch. A few exceptions were the animal proteinsources and some oilseed meals whose proteins may have been damaged during processing (Allan et al.,2000). Moreover, the apparent energy digestibility of peas as ingredient in some fish species (Table 8)could also reflect carbohydrate digestibility in the fish. This is because peas contain much higher amountsof carbohydrate than lipid (Muehlbauer and Tullu, 1997; Pulse Canada, 1999a; Racz, 1999) and the proteindigestibility coefficients for peas in different fish species (Table 8) are close. Moreover, the apparent energydigestibility coefficients reported for peas as ingredient are near the values for the carbohydrate digestibilityof soybean meal (54%), wheat grain (61%), and uncooked corn starch (55-61%) in blue tilapia (0. aureus)(NRC, 1993).Information on the use of P. sativum in fish diets is limited. Gomes et al. (1995) used feed pea at very a lowlevel (4% of the diet) together with other plant ingredients (faba bean meal, maize gluten, full-fat soybean,and a co-extruded mixture of peas and rapeseed) to partially substitute fish meal in rainbow trout diet. In astudy by Gouveia et al. (1993), pea seed meal was used at 38.2% of the diet (20% of the dietary protein) ofrainbow trout with or without cooking/expansion (145 º C, 25 kg per cm 2 ). The thermal treatment slightlyimproved the nutritional value of the diets containing the peas. In another study, there was a significantdecrease in the protein digestibility of the diet when the pea (P. sativum) in the diet of rainbow troutincreased from 25–50% (Pfeffer et al., 1995). Furthermore, the digestibility of the diets containing either 25or 50% peas increased significantly when the peas were autoclaved. APD coefficients of rainbow trout dietscontaining 25% feed peas increased from 86-91% when the peas had pre-treatment. For diets containing50% peas, APD increased from 83-86% when the peas were autoclaved (Pfeffer et al., 1995). In asubsequent study by Gouveia et al. (1998) on European sea bass (D. labrax), fishmeal-based dietscontaining 20 and 40% pea had APD coefficients of 88-89%. In the present study, the APD coefficients ofthe tilapia diets containing feed pea were high (90.5-92%) and were practically not affected by the dietarylevel of peas. This suggests that feed pea and the ingredients it replaced had similar protein digestibility.The whole peas with hulls were simply dried and ground. The digestibility of dehulled peas would mostlikely be higher in tilapia since dehulling removes most of the fiber of ingredients (Eusebio, 1991). Whencompared to other feedstuffs tested in tilapia, feed pea has APD coefficient that is comparable to that of fishmeal (Hanley, 1987; NRC, 1993; Jauncey, 1998). However, it is slightly lower than the protein digestibilityvalues reported for soybean meal (91-94%) in tilapia species (Hanley, 1987; Lim, 1987; Luquet 1991; NRC,1993).The protein content of feed peas is close to that of copra (coconut) meal, some cereal grain by-products,brewers' grains, and leaf meals (Gerpacio and Castillo, 1979; Hanley, 1987; Tacon, 1987; NRC, 1993;Hertrampf and Piedad-Pascual, 2000). The relatively low protein content of feed peas compared to fishmeal would limit the amount that could be incorporated in the diets of fish that require high protein levels.However, feed peas could be used as one of the ingredients that would collectively replace fish meal in apractical diet. Feed peas could also replace other plant protein sources, as shown in the present study,especially when its cost is competitive. Feed peas contain high levels of lysine (Pulse Canada, 1999a;Racz, 1999) which could complement the amino acids of other fishmeal substitutes that are deficient inlysine (e.g. canola meal and gluten meals). However, as in soybean meal and other legume seeds, thesulfur amino acids (methionine and cystine) are low and could be the first limiting amino acids when highamounts of plant protein sources are used. For fish requiring high dietary protein, pea protein concentrate(49% crude protein) has been explored as a possible partial replacement of fish meal (Carter and Hauler,2000). Up to 27% pea protein concentrate in the extruded feed did not affect growth of salmon parr. Cowpea (Vigna unguiculata) protein concentrate was also tested in Nile tilapia fry and up to 40% inclusion levelin the diet gave acceptable results (Olvera-Novoa et al., 1997).One important concern in the use of pulses as ingredients in aqua feeds is the presence of anti-nutritionalfactors (Tacon, 1987; Hertrampf and Piedad-Pascual, 2000). However, through genetic selection, presentpea varieties contain no tannins and only low levels of trypsin inhibitors and lectins (Bond and Duc, 1993)that can be deactivated by heat treatment (Melcion and van del Poel, 1993). Pulses are produced mainly fortheir mature seeds and immature pods for human consumption (Muehlbauer and Tullu, 1997), unlikesoybean and other oilseeds that are grown mainly for processing into edible oils and protein concentrates.With the expansion of production of feed peas as human food and animal feed (Pulse Canada, 1999b),more peas would be available in the market.15