VALIDATION OF THE ESSENTIAL AMINO ACID REQUIREMENTS OF NILE
TILAPIA, Oreochromis niloticus (LINNE 1758), ASSESSED BY THE IDEAL
PROTEIN CONCEPT
Oyedapo A. FAGBENRO
Department of Fisheries and Wildlife
Federal University of Technology
P.M.B. 704 Akure, Nigeria
ABSTRACT
Essential amino acid pattern of whole body of Oreochromis niloticus (Linne 1758), the most
important fish in African aquaculture, was determined in acid hydrolysates and using the
ideal protein concept (essential amino acid ratio), the essential amino acid requirements (g/kg
protein) were estimated as: arginine, 41; histidine, 15; isoleucine, 26; leucine, 43;
methionine+ cystine, 34; phenylalanine + tyrosine,48; threonine, 33; tryptophan,6; valine,30.
Except for higher leucine and lower phenylalanine + tyrosine requirements, estimated
requirements for the other essential amino acids were similar to the empirically determined
essential amino acids requirements of O. niloticus recorded in literature. This information is
useful in developing nutrient-balanced, cost-effective research diets and practical feeds for
other cultivated tilapias.
INTRODUCTION
The Nile tilapia, Oreochromis niloticus (Linne 1758), is the most important tilapia used in
African aquaculture, under both freshwater and brackishwater culture (FAO,1997) because of
their hardiness, fast growth and attainment of large size as adults. The level of fish feed
technology available to fish farmers in many African countries is low and fish feed
formulation programs are based on available information on the nutrient requirement data
given by NRC (1993). Essential amino acid requirements of several cultivated tilapias have
not been established but that of O. niloticus is available (Santiago & Lovell,1988). Essential
amino acid requirement values empirically determined for the Nile tilapia should suffice, but
NRC (1993) cautioned that essential amino acid requirements are not interchangeable among
species.
The concept of "an ideal protein" being used as a method of determining the essential amino
acid requirements of fish was suggested by Wilson (1991). This is based on the direct
correlation between essential amino acid pattern in fish tissues and dietary essential amino
acid requirement pattern. If the requirement for a single essential amino acid, for example
lysine (being the first limiting essential amino acid in most feedstuffs), and the whole body
essential amino acid pattern are known, dietary requirement for the other nine essential amino
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acids can be expressed relative to the lysine requirement using the essential amino acid ratio.
Wilson & Poe (1985) demonstrated that a direct correlation (r > 0.90) exists between whole
body essential amino acid pattern and essential amino acid requirement pattern of channel
catfish (Ictalurus punctatus) and it is assumed that such high correlation would also be true
for other fishes. Wilson (1991) applied the ideal protein concept to estimate the dietary
essential amino acid requirements of I. punctatus and reported close agreement with essential
amino acid requirement values determined by empirical methods. Woods & Soares (1996)
also used the ideal protein concept to estimate the dietary essential amino acid requirements
of striped bass (Morone saxatilis) broodstock. These workers also reported that amino acid
composition of the whole body of the fish did not change with the size of the fish.
The objectives of this study was to determine the whole body essential amino acid profile of
O. niloticus and based on the empirically determined dietary lysine requirements (Santiago &
Lovell,1988), its dietary essential amino acid requirement were estimated by the ideal protein
concept, and compared with the respective determined values in literature.
MATERIALS AND METHODS
Oreochromis niloticus fingerlings reared in an experimental earthen pond, were used for the
determination of whole-body amino acid composition. Triplicate samples were prepared by
taking 20 whole fish, oven-dried at 105oC for 24 h, finely powdered and sieved. Amino acid
composition in triplicate samples of fish tissue was determined in acid hydrolysate (6
mol/litre HCl under reflux for 24 h at 110oC) using an automatic amino acid analyser (LKB
4151 plus, Biochrom Ltd., Cambridge, UK). Tryptophan was determined colorimetrically
after hydrolysing triplicate samples in 4.2 mol/litre NaOH (Fischl,1960). From the wholebody amino acid composition, essential amino acid ratios were computed. The dietary
essential amino acid requirement pattern was estimated relative to the empirically determined
lysine requirement of 51 g lysine/kg protein (Santiago & Lovell,1988) as reference using the
ideal protein concept (Wilson,1991). Both sets of values were tested for statistical
significance (P < 0.05) with Product moment correlation test (r) using Statgraphics 3.1 for
windows on PC.
RESULTS AND DISCUSSION
The whole body essential amino acid pattern of O. niloticus is presented in Table 1. Using the
ideal protein concept (essential amino acid ratio), it translates to the estimated essential
amino acid requirement also presented in Table 1. Comparatively, the phenylalanine+tyrosine
requirements were higher while leucine was lower (P < 0.05) in the determined. The
estimated essential amino acid requirement of O. niloticus indicated a strong relationship (r =
0.92764) to the determined essential amino acid values reported by Santiago & Lovell (1988)
and to the whole body essential amino acid pattern (r = 0.924262). Thus, if the dietary lysine
requirement of a fish is known, the dietary requirement for the remaining essential amino
acids of the fish relative to the lysine requirement, could be estimated.
The dietary essential amino acid requirements determined using the ideal protein concept
(based on the whole body essential amino acid pattern) can serve as a valuable index for
formulating the diets of other cultivated tilapias until their dietary essential amino acid
2
requirements are empirically established using amino acid test diets. This procedure is much
less time consuming and less costly than determining amino acid requirements of the fish by
conventional means. As interest in commercial culture of other tilapias increase, so does the
need to optimize their diet. It is therefore concluded that this information on the requirement
for essential amino acids is useful in developing nutrient-balanced, cost-effective research
diets and practical feeds.
Table 1: Essential amino acid profile of Oreochromis niloticus tissues and the estimated
essential amino acid requirements (g/kg protein) using the ideal protein concept (essential
amino acid ratio).
Tissue
essential
amino acid
Essential
amino
acid ratio
Essential amino acid
requirement
Determined1
Estimated2
Arginine
89
79.5
42
41
Histidine
33
29.5
17
15
Isoleucine
58
51.8
31
26
Leucine
95
84.8
34*
43
Lysine
112
100
51
-
Methionine
Cystine
29
47
25.9
42.0
32
13
21
Phenylalanin
e
Tyrosine
71
34
63.4
30.4
57*
32
16
Threonine
73
65.2
36
33
Tryptophan
13
11.6
10
6
Valine
66
58.9
28
30
1
Santiago & Lovell (1988)
Ideal protein concept
* values are significantly different (P < 0.05) from estimated values.
2
3
ACKNOWLEDGEMENTS
Thanks to Alan Porter for the essential amino acid analyses conducted at the Fish Nutrition
Unit, Institute of Aquaculture, University of Stirling, Scotland, UK.
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