VALIDATION OF THE ESSENTIAL AMINO ACID …



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 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 whole-body 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 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 |Essential amino acid|Essential amino acid | |

| |amino acid |ratio |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 |29 |25.9 |32 |13 |

|Cystine |47 |42.0 | |21 |

| | | | | |

|Phenylalanine |71 |63.4 |57* |32 |

|Tyrosine |34 |30.4 | |16 |

| | | | | |

|Threonine |73 |65.2 |36 |33 |

| | | | | |

|Tryptophan |13 |11.6 |10 |6 |

| | | | | |

|Valine |66 |58.9 |28 |30 |

1 Santiago & Lovell (1988)

2 Ideal protein concept

* values are significantly different (P < 0.05) from estimated values.

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.

REFERENCES

Cowey, C.B.(1993) Recommendations of technical sessions. p.5, in J.M. Gropp and A.G.J. Tacon (eds.) Report of the EIFAC Workshop in Methodology for Determination of Nutrient Requirements in Fish. EIFAC/OP 29. FAO, Rome.

FAO (1997) Aquaculture Production Statistics, 1986-1995. FAO Fisheries Circular No.815 Rev.9. FAO, Rome. 195 pp.

Mohanty, S.N. & Kaushik, S.J.(1991) Whole body amino acid composition of Indian major carps and its significance. Aquatic Living Resources 4:61-64.

NRC (National Research Council)(1993) Nutrient requirement of fishes. National Academy of Sciences. Washington, DC, 114pp.

Tacon, A.G.J. (1987) The nutrition and feeding of farmed fish and shrimp - a training manual. 1. The essential nutrients. GCP/RLA/075/ITA, Field Document 2. FAO, Rome. 117pp.

Wilson, R.P.(1989) Protein and amino acid requirements of fishes. pp.51-76, in S.Y. Shiau (ed.). Progress in fish nutrition. Marine Food Science Series No.9. National Taiwan Ocean University, Keelung, Taiwan.

Wilson, R.P.(1991) Amino acid nutrition of fish: a new method of estimating requirement values. pp.49-54, in M.R. Collie and J.P. McVey (eds.) Proceedings of the US-Japan Aquaculture Nutrition Symposium. Newport, OR. October 28-29, 1991.

Wilson, R.P. & Poe, W.E.(1985) Relationship of whole body and egg amino acid patterns in channel catfish, Ictalurus punctatus. Comparative Biochemistry and Physiology 80B:385-388.

Woods, L.C. & Soares, J.H.(1996) Nutritional requirements of domestic striped bass broodstock. p.107, in D.A. Hannock and J.P. Beumer (eds.) Proceedings of the 2nd World Fisheries Congress, Brisbane, Australia. July 28-August 3,1996.

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