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Aquaculture 250 (

Apparent digestibility of selected feed ingredients for

Nile tilapia (Oreochromis niloticus)

Kenan Koprucu*, YaYar Ozdemir

Firat University, Fisheries Faculty, 23119, Elazig, Turkey

Received 28 September 2004; received in revised form 7 December 2004; accepted 7 December 2004

Abstract

In this study, apparent digestibility coefficients (ADCs) of nutrients and energy in selected feed ingredients were determined

for Nile tilapia. ADCs were determined using a reference diet with chromic oxide indicator and test diets that contained 70%

reference diet, by weight, and 30% of the test ingredient being evaluated. Fish were fed twice daily at the rate of 4% of their

body weight at 27F1 8C of water temperature. Fecal samples were collected from three replicate groups of fish using fecal

collection column attached to fish rearing aquaria. The ADCs of the anchovy meal, corn gluten meal, soybean meal, gammarid

meal and crayfish exoskeleton meal were: dry matter, 91.6%, 93.2%, 90.9%, 77.0%, and 75.7%; protein, 90.5%, 89.0%, 87.4%,

75.8% and 71.0%; lipid, 97.5%, 94.0%, 92.1%, 75.8%, and 72.0%; fiber or chitin, 90.1%, 96.1%, 95.2%, 71.5%, and 69.3%;

ash, 38.1%, 74.9%, 71.6%, 32.4%, and 30.8%; calcium, 17.1%, 20.3%, 20.9%, 13.2%, and 11.6%; phosphorus, 27.8%, 28.2%,

30.1%, 10.5%, and 9.7%; nitrogen-free extract 93.7%, 95.8%, 92.6%, 84.2%, and 82.7%; energy, 92.1%, 89.0%, 83.7%,

65.6%, and, 54.8%; and average amino acid, 91.2%, 89.6%, 87.1%, 76.2%, and 70.6%, respectively. These values were

significantly affected by test ingredients (Pb0.05). The results of the study suggest that the ADCs of protein are indicative of

amino acid digestibility. However, variation in individual amino acid digestibility between feed ingredients means that

determination of this parameter may allow more accurate and economical feed formulation.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Nile tilapia; Apparent digestibility; Feed ingredients; Nutrients; Energy

1. Introduction

A feed ingredient may appear from its chemical

composition to be an excellent source of nutrients

but will be of little actual value unless it can be

0044-8486/$ - see front matter D 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.aquaculture.2004.12.003

* Corresponding author. Tel.: +90 424 237 0000x6111; fax: +90

424 238 6287.

E-mail address: kkoprucu@firat.edu.tr (K. Koprucu).

digested and absorbed in the target species. Knowl-

edge of nutrient digestibility of the various feed

ingredients used in formulating fish feeds is

desirable so that effective substitution of one

ingredient for another may be achieved. Together

with chemical analysis, digestibility determination

may allow a more thorough estimation of the

nutritive value of a particular protein source in a

complete feed for fish.

2005) 308–316

Table 1

Composition of the reference and test diets (%)

Ingredients Reference diet Test diets

Anchovy meal 15

Soybean meal (solvent extracted) 43

Wheat flour 38.7

Sunflower oil 1.9

Antioxidanta 0.1

Vitamin premixb 0.25

Mineral premixc 0.05

Chromic oxide (Cr2O3) 1

Reference diet 70

Test ingredient 30

K. Koprucu, Y. Ozdemir / Aquaculture 250 (2005) 308–316 309

The tilapia feeds efficiently on natural fauna and

flora and can utilize supplementary feed materials to

achieve rapid growth and weight gain. The intensi-

fication of tilapia culture requires the development of

suitable feeds both for complete and supplementary

feeding in tanks and ponds. The nutritive value of

mixed rations depends on the nutrient composition of

the individual feed components and the ability of the

animal to digest and absorb the nutrients (Moreau,

1996; Watanabe et al., 1996; Degani et al., 1997;

Falaye and Jauncey, 1999; Riche et al., 2001). For

tilapia feeds typical protein sources examined have

included poultry by-product (Gaber, 1996), cacao

husks (Pouomogne et al., 1997), legume seed meal

(Fagbenro, 1998), defatted soybean meal, full-fat

toasted soybean, lupin seed meal and faba bean meal

(Fontainhas-Fernandes et al., 1999), sunflower cakes,

fish (anchovy) meal and wheat bran (Maina et al.,

2002), cottonseed meal, sunflower meal (El-Saidy

and Gaber, 2003), fish and poultry meals, corn

gluten, rapeseed meal, sorghum, barley (Sklan et al.,

2004). Anchovy meal, corn gluten meal, soybean

meal, gammarid meal and crayfish exoskeleton meal

were selected as dietary protein sources on the basis

of their availability and use in tilapia feeds in

Turkey. Gammarid (Mathias et al., 1982; Ozdemir

et al., 1997; Koprucu et al., 1998) and crayfish

exoskeleton (Ozdemir et al., 1999) have high protein

levels and favourable essential amino acid profiles,

but ash and chitin contents of these feed ingredients

are very high. The ability of fish to digest and absorb

gammarid and crayfish (crustacean) exoskeleton

meals as feed is not well understood (Forster,

1999; Shiau and Yu, 1999). The total production of

crustacea in the world and Turkey was about

935,000 and 220 tonnes in 1995, respectively

(FAO, 1995).

The objective of this study was to determine the

apparent digestibility of nutrients and energy in

selected feed ingredients for Nile tilapia.

Total 100 100

a Antioxidant (mg/g): butylated hydroxytoluene, 12.5.b Vitamin premix contains (IU or mg/g of premix): retinol, 1600

IU; calciferol, 800 IU; tocopherol, 20; menadione, 4; thiamine, 4

riboflavin, 6; niacin, 12; pantothenic acid, 20; pyridoxine, 4

cobalamin, 0.008; folic acid, 2; biotin, 0.4; choline chloride, 200

ascorbic acid, 80.c Mineral premix contains (mg/g of premix): manganese 50, iron

88, zinc 200, copper 6, iodine 10, selenium 0.6.

2. Materials and methods

2.1. Fish and experimental condition

This study was conducted at the fish reproduction

unit of the Fisheries Faculty of Firat University,

Elazig, Turkey. Each treatment had three replicates, 15

Nile tilapia per replicate, with mean initial fish

weights of 15F0.1 g. Each treatment combination

was randomly assigned to three glass aquaria (25 l).

Water temperature in the aquaria was maintained at

27F1 8C and the fish were subjected to a 12 h

photoperiod using fluorescent lights. The water was

constantly replaced in the aquaria by continuous flow

at a rate of 250 ml min�1 to provide oxygen and

remove excess nitrogenous wastes.

2.2. Diet preparation

The reference diet (Table 1) was formulated to

satisfy the nutrient requirements of Nile tilapia

(Lovell, 1989). Chromic oxide (Cr2O3) was used as

an inert marker at a concentration of 1% in

reference diet. Test ingredients were obtained from

a local supplier (Elazig Feed Manufacture, Elazig,

Turkey). Chromic oxide was donated by Merck

Products. Vitamin and mineral premixes were

obtained from Roche Products.

Test ingredients for apparent digestibility were

anchovy meal (mechanical extracted), corn gluten

meal (dehydrated), soybean meal (solvent extracted

with hexane), gammarid (Gammarus kischineffensis)

;

;

;

K. Koprucu, Y. Ozdemir / Aquaculture 250 (2005) 308–316310

meal (cooked in 65 8C and ground in 0.2 mm size),

and freshwater crayfish (Astacus leptodactylus

leptodactylus) exoskeleton meal (cooked in 65 8Cand ground in 0.2 mm size). Five test diets were

formulated using 70% reference diet and 30% of

each of the test ingredients on an air-dry basis as

described by Cho and Slinger (1979). Test diets

contained 0.7% chromic oxide. Proximate and

amino acid composition of the test ingredients and

diets are shown in Table 2 and 3, respectively.

Diets were mechanically mixed with distilled water

(40 g/100 g diet mix), pressure-pelleted, and

Table 2

Proximate and amino acids composition of the ingredients used to test di

Components (% in dry matter) Test ingredients (International Feed N

AMa (5-01-985) CGMb (5-28-24

Dry matter 92.1 91.4

Crude protein 71.1 66.2

Crude lipid 8.3 2.1

Crude fiber or chitin* 1.1 1.8

Ash 14.2 2.5

Nitrogen-free extractf 5.3 27.4

Calcium 4.1 0.2

Phosphorus 2.9 0.5

Gross energy (kcal g�1) 5.1 5.4

Amino acidsg

Arginine 3.9 1.6

Histidine 1.7 1.4

Isoleucine 3.2 2.7

Leucine 5.1 10.1

Lysine 5.2 1.2

Methionine 2.1 1.7

Cystine 0.7 0.7

Phenylalanine 2.8 4.1

Tyrosine 2.3 3.4

Threonine 2.9 2.2

Valine 3.6 3.2

Alanine 5.3 5.4

Aspartic acid 6.8 5.0

Glutamic acid 10.2 12.6

Glycine 6.6 1.4

Proline 5.3 7.3

Serine 2.7 2.0

a AM: Anchovy meal.b CGM: Corn gluten meal.c SM: Soybean meal.d GM: Gammarid meal.e CEM: Crayfish exoskeleton meal.f Nitrogen-free extract calculated by difference.g Tryptophan could not be analysed because of its destruction during ac

subsequently dried in a current of air at room

temperature for 24 h. After that, the feeds were

then broken up and sieved into convenient pellet

sizes (3–5 mm) for the fish and stored in polythene

bags at 4 8C until used. The amount of diet needed

weekly was then kept at room temperature (Bureau

et al., 1999).

2.3. Feeding and fecal collection

The fish were acclimated to the experimental

system for 7 days before the start of the experiment.

ets (n=3)

umber of ingredients)

2) SMc (5-04-604) GMd (5-16-423) CEMe (5-04-226)

90.8 90.9 90.7

53.7 43.9 38.4

1.0 12.3 6.9

3.9 6.6* 10.2*

6.2 27.5 30.0

35.2 9.7 14.5

0.3 2.7 11.5

0.7 2.0 2.1

4.6 3.3 2.7

3.7 3.2 2.8

1.3 1.3 1.1

2.2 1.9 1.8

3.7 3.4 3.2

3.2 3.0 2.6

0.7 1.1 1.0

0.6 0.5 0.7

2.5 2.3 1.8

1.8 1.9 1.6

1.9 2.1 1.7

2.6 2.3 2.1

3.0 2.7 2.4

6.1 4.9 4.1

10.0 6.8 5.6

2.5 2.3 2.1

4.8 2.0 1.8

2.4 1.9 1.6

id hydrolysis.

Table 3

Proximate and amino acids composition of the reference and test diets (n=3)

Components (% in dry matter) Reference diet Test diets (70% reference diet+30% test ingredient)

AMa CGMb SMc GMd CEMe

Dry matter 95.0 95.1 94.8 94.9 95.0 94.7

Crude protein 40.0 49.3 47.9 44.1 41.2 39.5

Crude lipid 3.9 5.2 3.4 3.0 6.4 4.8

Crude fiber or chitin* 2.7 2.2 2.4 3.1 3.9 * 5.0 *

Ash 5.6 8.2 4.7 5.8 12.2 12.9

Nitrogen-free extractf 47.8 35.1 41.6 44.0 36.3 37.8

Calcium 0.8 1.8 0.6 0.6 1.3 4.0

Phosphorus 0.9 1.5 0.8 0.9 1.2 1.3

Gross energy (kcal g�1) 4.7 4.8 4.9 4.7 4.3 4.1

Amino acidsg

Arginine 2.6 3.0 2.3 2.9 2.8 2.7

Histidine 1.0 1.2 1.1 1.1 1.0 1.0

Isoleucine 1.7 2.2 2.0 1.9 1.8 1.7

Leucine 2.8 3.5 4.4 3.1 3.0 2.9

Lysine 2.6 3.4 2.2 2.8 2.7 2.6

Methionine 0.7 1.2 1.0 0.7 0.6 0.5

Cystine 0.5 0.6 0.6 0.5 0.5 0.6

Phenylalanine 1.7 2.0 2.4 1.9 1.9 1.7

Tyrosine 1.3 1.6 1.9 1.5 1.6 1.5

Threonine 1.5 2.7 2.3 1.6 2.0 1.6

Valine 2.0 2.5 2.4 2.2 2.1 2.0

Alanine 2.2 3.1 3.2 2.5 2.4 2.3

Aspartic acid 5.0 5.3 5.0 5.2 4.9 4.8

Glutamic acid 6.8 7.8 8.5 7.7 6.7 6.4

Glycine 2.5 3.1 2.2 2.5 2.4 2.4

Proline 2.9 3.6 4.2 3.5 2.6 2.6

Serine 1.7 2.0 1.8 1.9 1.8 1.7

a AM: Anchovy meal.b CGM: Corn gluten meal.c SM: Soybean meal.d GM: Gammarid meal.e CEM: Crayfish exoskeleton meal.f Nitrogen-free extract calculated by difference.g Tryptophan could not be analysed because of its destruction during acid hydrolysis.

K. Koprucu, Y. Ozdemir / Aquaculture 250 (2005) 308–316 311

Fecal collection started 4 days after changing to the

experimental diets to allow evacuation of all previ-

ously ingested material. Fecal samples were collected

using fecal collection column described by Cho et al.

(1982). The velocity of the water flow was adjusted to

minimize collection of the feces in the drainpipe and

maximize recovery of the feces in the collection

column.

During the trial, fish were fed twice daily (09:00

and 17:00 h) at the rate of 4% of their body weight.

About 30 min after the every feeding, the drainpipe

and the collection column were brushed out to remove

feed residues and feces from the system. Fecal

samples were collected by collection column for each

replicate twice daily, morning and evening for 30

days. The settled feces and surrounding water were

gently withdrawn from the base of the collection

column into a centrifuge bottle.

For all treatment groups, twice daily feces

collections were centrifuged at 5000 �g for 15

min and the supernatant discarded. The feces were

then freeze-dried, ground using a 1 mm screen, and

stored at �35 8C until required for analysis (Windell

et al., 1978; Vandenberg and De la Noue, 2001).

K. Koprucu, Y. Ozdemir / Aquaculture 250 (2005) 308–316312

Fecal samples from each aquaria were pooled at the

end of the experiment.

2.4. Analytical methods

Diets and fecal samples were analysed in

triplicate for proximate composition (AOAC,

1995) and chromic oxide (Furukawa and Tsuka-

hara, 1966). These samples were analysed for dry

matter at 65 8C for 24 h in a vacuum oven. Crude

protein (%N�6.25) was determined by the Kjeldahl

method using an Auto Kjeldahl System, lipid by

ether extraction and fiber by drying and ashing

after the extraction with 0.5 M H2SO4 and 0.5 M

NaOH. Ash content was determined after inciner-

ation at 550 8C for 12 h in a muffle furnace.

Calcium and phosphorus were analysed using an

atomic emission spectrometry. Nitrogen-free extract

was calculated by difference. Energy contents were

analysed using an Automatic Adiabatic Bomb

Calorimeter.

Amino acid content of fecal samples from each

aquaria, test ingredients and feeds were also deter-

mined. Amino acid analyses were performed using an

LC 3000 model amino acid analyser according to the

manufacturer’s recommendations for protein hydro-

lysates (Sarwar and Botting, 1993). Tryptophan could

not be analysed because of its destruction during acid

hydrolysis.

The apparent digestibility coefficients (ADCs) of

dry matter, protein, lipid, fiber, chitin, ash, calcium,

phosphorus, nitrogen-free extract, amino acids and

energy for the test ingredients and diets were calculated

as follows (Cho and Slinger, 1979):

ADC ¼ 100� 1� F=Dð Þ � Di=Fið Þ½ �

ADCI ¼ ADCT � 0:7� ADCRÞð �=0:3½

where:D=% nutrient or energy of diet; F=% nutrient or

energy of feces; Di=% marker (Cr2O3) in diet; Fi=%

marker (Cr2O3) in feces, ADCT=% apparent digesti-

bility coefficient of nutrient or energy in test diet;

ADCR=apparent digestibility coefficient of nutrient or

energy in the reference diet; I=test ingredient under

investigation.

2.5. Statistical analyses

Data were subjected to one-way ANOVA. When

appropriate, the Duncan’s New Multiple Range test

was applied to evaluate difference between means.

3. Results

Apparent digestibility coefficients (ADCs) of dry

matter, protein, lipid, fiber, chitin, ash, calcium,

phosphorus, nitrogen-free extract, energy, and amino

acids in the selected test ingredients for Nile tilapia are

shown in Table 4. The ADC values of nutrients and

energy were significantly affected by test ingredients

(Pb0.05).

ADCs of dry matter and nitrogen-free extract in

anchovy meal, corn gluten meal and soybean meal

were significantly higher (Pb0.05) than gammarid

meal and crayfish exoskeleton meal. There were no

significant differences in ADCs of dry matter and

nitrogen-free extract between gammarid meal and

crayfish exoskeleton meal.

ADCs of protein and average amino acid were found

as 90.5% and 91.2% for anchovy meal, 89.0% and

89.6% for corn gluten meal, 87.4% and 87.1% for

soybean meal, 75.8% and 76.2% for gammarid meal,

71.0% and 70.6% for crayfish exoskeleton meal. ADCs

of average amino acid for the test ingredients followed

similar trend to ADCs of protein. ADCs of protein and

average amino acid in anchovy meal, corn gluten meal

and soybean meal were significantly higher (Pb0.05)

than gammarid meal and crayfish exoskeleton meal.

Differences in ADCs of protein and average amino acid

between gammaridmeal and crayfish exoskeletonmeal

were found significant (Pb0.05).

The anchovy meal had higher ADCs of lipid

(Pb0.05) than that of soybean meal, gammarid meal

and crayfish exoskeleton meal but no differences

between the corn gluten meal with anchovy meal and

soybean meal. ADCs of phosphorus were significantly

different among test ingredients (Pb0.05, except for

anchovy meal and corn gluten meal). Differences in

ADCs of fiber or chitin, ash and calcium between

anchovy meal and others test ingredients were found

significant (Pb0.05) but no differences between the

corn gluten meal and soybean meal or gammarid meal

and crayfish exoskeleton meal.

Table 4

Apparent digestibility of nutrients and energy in the test ingredients for Nile tilapia

Components (%)a Reference diet Test ingredients

AMb CGMc SMd GMe CEMf SEMg

Dry matter 89.0 91.6b 93.2b 90.9b 77.0c 75.7c 0.38

Protein 87.1 90.5b 89.0b 87.4b 75.8c 71.0d 0.39

Lipid 90.6 97.5b 94.0b,c 92.1c 75.8d 72.0e 0.52

Fiber or Chitin* 88.0 90.1b 96.1c 95.2c 71.5d * 69.3d * 0.58

Ash 63.5 38.1b 74.9c 71.6c 32.4d 30.8d 0.98

Nitrogen-free extract 88.7 93.7b 95.8b 92.6b 84.2d 82.7d 0.27

Calcium 18.4 17.1b 20.3c 20.9c 13.2d 11.6d 0.19

Phosphorus 25.7 27.8b 28.2b 30.1c 10.5d 9.7e 0.46

Energy 81.8 92.1b 89.0c 83.7d 65.6e 54.8f 0.72

Amino acids

Arginine 89.3 92.1b 88.9b 88.7b 77.0c 71.5d 0.39

Histidine 90.1 92.4b 90.0b 88.9b 79.2c 72.3d 0.38

Isoleucine 82.7 90.7b 89.5b 86.1c 70.5d 65.2e 0.52

Leucine 86.6 90.8b 87.7b,c 86.5c 77.0d 69.5e 0.41

Lysine 88.1 90.5b 88.0b,c 83.4c 76.7d 70.1e 0.40

Methionine 86.6 94.0b 94.1b 84.0c 70.3d 67.0d 0.57

Cystine 86.2 89.6b 86.7b,c 86.0c 72.7d 68.9e 0.43

Phenylalanine 88.5 90.0b 90.3b 87.2b 79.2c 70.0d 0.39

Tyrosine 89.0 90.5b 86.0c 85.7c 80.3d 72.7e 0.33

Threonine 86.1 90.1b 88.5b 86.9b 77.0c 68.1d 0.42

Valine 86.0 90.3b 88.6b 83.5c 76.1d 69.7e 0.40

Alanine 84.9 93.2b 94.0b 86.0c 74.1d 68.3e 0.51

Aspartic acid 85.8 91.4b 89.4b 88.0b 78.6c 72.9d 0.37

Glutamic acid 90.7 92.8b 90.2b 92.1b 78.4c 71.3d 0.43

Glycine 87.1 90.4b 91.9b 89.0b 79.0c 77.0c 0.31

Proline 91.0 91.2b 90.1b 90.5b 77.0c 74.6c 0.37

Serine 86.8 91.6b 89.9b,c 88.0c 72.7d 70.4d 0.45

Average AAADh 87.7 91.2b 89.6b 87.1b 76.2c 70.6d 0.41

a Standard error of the treatment mean (SEM) calculated from the residual mean square in the analyses of variance.b AM: Anchovy meal (5-01-985).c CGM: Corn gluten meal (5-28-242).d SM: Soybean meal (5-04-604).e GM: Gammarid meal (5-16-423).f CEM: Crayfish exoskeleton meal (5-04-226).g Coefficients (mean of three replicate groups) in each row with a different letter are significantly different ( Pb0.05).h Average AAAD: Average apparent amino acid digestibility.

K. Koprucu, Y. Ozdemir / Aquaculture 250 (2005) 308–316 313

ADCs of energy were significantly (Pb0.05) differ-

ent among ingredients tested. Anchovy meal had the

highest (92.1%) ADCs of energy whereas crayfish

exoskeleton meal had the lowest (54.8%) ADCs of

energy (Table 4).

4. Discussion and conclusion

Generally, the protein quality of dietary ingredients

is the leading factor affecting fish performance, and

protein digestibility is the first measure of its

availability by fish. Protein quality of dietary protein

sources depends on the amino acid composition and

their digestibility. Deficiency of an essential amino

acid leads to poor utilization of the dietary protein and

consequently reduces growth and decreases feed

efficiency (Halver and Hardy, 2002).

Although the data presented in this study suggest

a reasonable agreement between ADCs of protein

and average amino acid, ADCs of individual amino

acids within a feed ingredient are variable. Since

K. Koprucu, Y. Ozdemir / Aquaculture 250 (2005) 308–316314

ADCs of especially essential amino acids, nutrients

and energy for selected protein sources used in this

study have not been reported for Nile tilapia, use of

the ADCs obtained from this study should allow

for more accurate and economical tilapia feed

formulation.

The present study showed that ADCs of dry matter,

protein, lipid, fiber, chitin, ash, calcium, phosphorus,

nitrogen-free extract, average amino acid, and energy

in the test ingredients for Nile tilapia were affected by

test ingredients (Pb0.05). The differences in ADCs of

nutrients and energy may be explained by differences

in chemical composition, origin and processing of

these feed ingredients (Table 2). ADCs of protein and

average amino acid were highest in feed ingredients

with high protein and low ash contents. Especially,

ADCs of dry matter, protein, average amino acid,

lipid, and energy in crayfish exoskeleton meal and

gammarid meal were significantly lower than those of

other test ingredients, and this trend may be due to

high content of ash (30.0% and 27.5%, respectively)

and chitin (10.2% and 6.6%, respectively) in these

ingredients. Shiau and Yu (1999) revealed lower lipid

and dry matter digestibilities of tilapia fed diets

containing high chitin (10%). Studies with rainbow

trout also indicated that chitin was not digested when

feed at 10% and 30% of the diet (Lindsay et al.,

1984).

The ADCs for protein in protein-rich feed ingre-

dients are usually in the range of 75–95%. The ADCs

of protein (71–90.5%) in test ingredients for Nile

tilapia in our study (fecal samples collected using

fecal collection column) are generally in agreement

with the reported ADCs of protein in various feed

ingredients for Nile tilapia. For example, alfalfa (66%)

and fish (menhaden, 85%) meals (feces collected by

frequent removal from water) (Pompa, 1982); corn

(83–84%), soybean (91–94.4%) and fish (sardine,

86%) meals (fecal samples collected by dissection)

(Hanley, 1987); defatted soybean meal (94.4%), full-

fat soybean (90%) and micronized wheat (88.6%)

(feces collected by the Guelph system) (Fontainhas-

Fernandes et al., 1999); anchovy meal (90%), sun-

flower cakes (86–89%) and wheat bran (75%) (Maina

et al., 2002). Part of the variability in ADCs of protein

may explain by differences in chemical composition,

origin and processing of these various feed ingre-

dients, and methods of feces collection. Bureau et al.

(1999) reported that the difference in the ADCs

obtained when using fecal samples collected by

stripping vs. with the Guelph system and the need

to report the method used to collect fecal material

when comparing estimates of apparent digestibility

among studies.

Fat when administered either alone or in a mixed

diet routinely gives digestibility values range from

85% to 95% for fish (Cho and Slinger, 1979; Aksnes

and Opstvedt, 1998). Sklan et al. (2004) reported that

for tilapia the ADCs of lipid (72–90%) and energy

(39–89%) for fish and poultry meals, corn gluten,

soybean meal, rapeseed meal, sunflower seed meal,

wheat, corn, sorghum, barley and wheat bran. The

ADCs of lipid (72–97.5%) and energy (54.8–92.1%)

in test ingredients for Nile tilapia in our study are

generally in agreement with that reported by Sklan et

al. (2004).

The apparent phosphorus digestibility coefficients

of anchovy meal (27.8%), corn gluten meal (28.2%)

and soybean meal (30.1%) for Nile tilapia in our study

are higher than the reported ADCs of phosphorus in

brown fishmeal (24%) for common carp (Ogino et al.,

1979), corn (25%) and soybean meal (29%) for

channel catfish (Wilson et al., 1982). Tilapia and

salmonids utilize phosphorus present in fish meal

more efficiently than do carp and channel catfish

(NRC, 1993). The differences in the bioavailability of

phosphorus to salmonids and tilapia or carp is

probably due to the limited secretion of gastric juices

by these warmwater species (Ogino et al., 1979).

In conclusion, data presented here suggest a

reasonable agreement between ADCs of protein and

average amino acid and, in general, the protein

digestibility coefficients were indicative of amino

acid digestibility. The results of the study suggest that

protein digestibility coefficients are indicative of

average amino acid digestibility. However, because

of variation within individual amino acid availabilities

between feed ingredients, the use of specific amino

acid digestibility coefficients may allow more accu-

rate and economical feed formulation.

Acknowledgements

This research was funded by the support from

the Firat University, Unit of Scientific Research

K. Koprucu, Y. Ozdemir / Aquaculture 250 (2005) 308–316 315

Projects, under agreement No: FUBAP-680. The

authors gratefully acknowledge the Cukurova Uni-

versity, Fisheries Faculty (Adana, Turkey) for

provision of fish samples.

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