A COMPARISON OF MACRONUTRIENT LEVELS IN GREEN MUSSEL (PERNA VIRIDIS) AND BROWN MUSSEL (MODIOLUS METCALFE/ HANLEY)
THAMNOON ROCHANABURANON
Department of General Science, Faculty of Science, Chulalongkorn University, Phya Thai Road, Bangkok, Thailand and Aquaculture Research Methodology Program, Southeast Asian Fisheries Development Center (SEAFDEC), Tigbauan, lloilo, Philippines
(Received 20 September 1980)
Summary
Two species of mussel from Panay Island, Philippines, have been analyzed for moisture, crude protein, crude fat, ash, carbohydrate, crude fibre and minerals (calcium and phosphorus). Results showed that the brown mussel (Modiolus metca/fei), both the marketable size and the small ones, have higher protein content (71.49 and 67.10% dry weight) than the maketable-size green mussel (Perna viridis}, 63.94%. The green mussel contained more fat but less ash, crude fibre and minerals than the brown mussel.
Introduction
Protein derived from fishmeal has been shown to be very efficient nutrient, although rather difficult to obtain and expensive. Besides fish, meat, poultry and plant protein, shellfish is one of the possible protein sources to be utilized. Among the latter, mussel seems to be much cheaper than the others such as shrimp which are well acceptable in terms of food and feed nutrition for aquaculture. The green mussel (Tahong in Tagalog), Perna viridis, formerly known as Mytilus smaragninus and the brown mussel, Modiolus metcalfei, are the species which have some status in aquaculture area. The former is a species popularly consumed by man and the latter is used as food for other economically important species such as Penaeus monodon Fabricius and Scylla serrata Forskal. Besides these, the common green mussel, Mytilus edulis, proved to be very good and acceptable food for rearing the prawn, Crangon crangon L. and the shrimp, Palaemon elegans Rathke from early juvenile up to complete reproductive cycle in the laboratory 1• Kanazawa2 has revealed that brown mussel fed to prawn gave a high growth rate. Knowledge of mussel macronutrient contents, namely moisture, protein, fat, carbohydrate, crude fibre, ash and minerals leads to a better understanding of their nutritional values, leading in turn to improvement of diet for feeding different commercial species.
Natural population of the green mussel, Perna viridis, within the Philippine archipelago (Fig. 1) are found only in scattered pockets. Natural settlements appear

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PHILIPPINES
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LEGAN ES GUIMARAS ISLAND
HIMAMAYLAN BOHOL ISLAND

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Fig. 1.

restricted to estuarine areas in Manila Bay, the Northern shores of Panay Island, the Iloilo strait, the western shore of Negros Island, and western Samar Island. The shallow subtidal species of brown mussel, Modiolus metcalfei, is more widespread than P. viridis and is normally found embedded in muddy substrates, attached to each other just below low tide levels. It is observed to occur together with the green mussel in all known green mussel areas. However, very low numbers have been found in clusters of green mussel growing off-bottom. In purely known mussel areas the spats do not settle on the surface of the bamboo fish corals or other similar structures in the water. This settlement preference evolved as a survival mechanism, since in a brown mussel bed living mussel valves provide refuge 'from the muddy bottom which smooths a newly settled mussel3 • 4• However, it appears that most of the green mussel live just below the surface in the protective area where the water is clean and less turbid whereas the brown mussel occupies the silty bottom within the less protective area.
Both endogenous and exogenous factors may be responsible for difference in macronutrient levels and biochemical composition of the mussels. The endogeous factors consist of genetic difference, physiological status, reproductive cycle, feeding habit, etc. The exogenous factors are habitat, abundance of food available, temperature, size, dissolved organic matter/debris, soil composition, starvation, and time available for feeding, etc. Bayne et al.5 stated that biochemical content is dependent on size and growth of the animal. Changes in body weight are mainly due to changes in carbohydrate or glycogen content. The seasonal cycles for storage and utilization of glycogen resources reflect the complex interactions between food
supply and temperature, and between growth and the annual reproductive cycle. According to biochemical data5, glycogen accumulates mainly during the reproductive period. After the mussel become spent the metabolic energy demand is low. Whenever abundant food is available in the plankton there is a marked increase in glycogen with the highest accumulation in the mantle. Protein and lipid resources are also built up. Lipid level is generally higher in the adult female than in the
male or the young mussel presumably due to the fatty resources in: the eggs. Organic matter and debris supplies a large part of the mussel's diet and bacteria may be utilized as food also. Mytilus edulis is capable of assimilating dissolved organic solutes present in the environment. Other factors such as brackish estuaries condition or mangrove area is known to be suitable for mussel growth but this is probably a function of improved feeding conditions rather than salinities5• Animals in poor
condition such as in the laboratory are considered to be under stress and starvation. During the starvation individuals of all· size showed a reduction in carbohydrate and lipid. This reduction was particularly marked in smaller individuals, which probably have less carbohydrate and lipid than the larger ones. Genetic differences are very prominent among the bivalves. There is an impressive amount of genetic differentiation among samples less than one meter apart, indeed among individuals of different sizes. Microgeographic variation demonstrated genetic heterogeneity over small distances, primarily· over tidal flats, in estuaries, and among different levels in the intertidal zone where exposure time, tempe·rature, heat transfer and water reten· tion are dramatically different.

The objective of this work is to compare the macronutrient levels {moisture, crude protein, crude fat, crude fibre, crude carbohydrate, ash and mineral) between
Perna viridis and Modiolus metcalfei, in order to see whether there are any differences in these parameters due to genetic factors, size, and habitats.

Materials and Methods
Both green and brown mussels were collected from the field and preconditioned in the mussel laboratory at SEAFDEC, Tigbauan prior to the analysis. They were classified into 3 groups according to their species and sizes : green, brown and small brown mussels, Their collection site and pre-conditioning were recorded and shown in Tables 1 and 2.

TABLE J. COLLECTION DATA OF GREEN, BROWN AND SMALL MUSSELS

Species (Size)

Collection site

Time and date of collection

Condition of tide

Approximate age
of samples (month)

Other observations

Depth (meter)

Water current

Green mussel Banate Bay, (marketable) Panay Island

Afternoon July 23, 1979

Low tide

Brown mussel (marketable)
Brown mussel (small)

Estancia, Panay Island
Banate Bay, Panay Is.

Morning July 21, 1979
Afternoon July 23, 1979

Lowtide Lowtide

12 2 Rapid water exchange,
current speed moderate
8

2

Exposure

None

only a few

cm.

TABLE 2. PRE-CONDITIONING OF GREEN AND BROWN MUSSELS BEFORE ANALYSIS
Mussels were transported from collection sites to Tigbauan and pre-conditioned in flow-through sea water.

Condition Temperature
("C)
Salinity
(%)
Time& date
Transportation technique

Green Mussel 30.0°
33.3°
10:00 a.m. July 24, 1979 Moist Deutsch sack

Brown mussel 30.5°
30.0"
7:00 a.m. July 22, 1979 Moist Deutsch sack

Small brown mussel 27.0°
30.0"
10:00 a.m. July 24, 1979 Moist Deutsch sack packed in mud

After a pre-conditioning period in the mussel laboratory for 3-1 days, the
samples were taken out for analysis. The proper pre-conditioning duration was kept less than 24 hours in order to eliminate all undigested food. The number of individuals was limited to its availability. All mussels were measured for their total length (from the tip of umbo to the posterior end of the shell) and mussel flesh weight were not for each species as shown in Table 3.

TABLE 3. SIZE PARAMETERS OF THE GREEN, BROWN AND SMALL BROWN MUSSELS

Sample
Green mussel
Brown mussel
Small brown mussel

Total length range &
Mean (cm)
6.37-10.15 8.38
5.14-6.84 5.80
2.29-4.14 2.99

Total wet weight (g)
539.32
156.21
108.81

Dry weight (g) &
Dry matter ('7{,)
99.90 18.52
33.35 21.35
24.42 22.44

Total number of individuals 50
50
350

The mussel flesh was chopped and dried in an oven (100-I I0°C) to constant weight. The sample was homogenized by grinding with a mortar and pestle. The resulting powder was placed in covered glass bottles and stored in a dessicator for subsequent analysis. The method used in proximate and mineral analysis was based on the adapted procedure of the AOAC6 and Laboratory Manual For Fish Feed Analysis7• Protein was analysed by the semi-micro Kjeldahl method; fat, by Soxhlet extraction with ether; moisture, by loss in weight on drying at 105°C; crude fibre, by weak acid and base digestion followed by ignition of the dried residue at 550°C; ash, by ignition at 550°C; and carbohydrate by difference. The ash was dissolved in HCl-HN03 solution at just below boiling, made up to volume with distilled water and used in mineral analysis by titration method for calcium and U.V. spectrophotometry for phosphorus.
Results
The results of the determinations are given in Table 4. Moisture is slightly different in the 3 samples, the larger the higher. The two brown mussels contain relatively higher percentage of protein than the green mussel although lower in shell length and wet weight. However, crude fat is higher in the green mussel than the brown and small brown mussels. The small brown mussels seem to have more ash than the green the larger brown mussel. The carbohydrate content of brown mussel is less than the green and the smal. brown ones. The green mussel, however, possesses smaller amount of crude fibre as well as calcium in comparison with the other two brown mussels. Phosphorus content is least in the small brown mussel, followed by the green mussel.

TABLE 4. MACRONUTRIENT CONTENTS OF GREEN. BROWN AND SMALL BROWN MUSSELS EXPRESSED AS PERCENT DRY WEIGHT
Figures are given as mean percentage + standard deviation.

Macronutrient
Moisture Crude protein
Crude fat Crude fibre
Ash Crude carbohydrate
Calcium Phosphorus

Green mussel
81.48
63.94 + .431 9.45 ± .050 0.06 + .256 11.49 + .256
15.060
0.305 + .271 0.894 + .036

Brown mussel
78.65
71.49 + .395 6.56 + .252 0.095 + .005 12.51 + .265
9.345
0.356 + .029 1.172 + .126

Small brown mussel
77.56
67.10 + .614 4.27 + .242 0.115 + .01 13.98 + .332
13.790
0.414 + .034 0.632 + .019

The following conclusion could be drawn from the experiment based on F-Test and Duncan Multiple Range Test:
I. The green mussel, brown mussel and the small brown mussel have different protein, crude fat and also phosphorus contents (P <.01).
2. There is a difference in ash content between the small brown mussel and the green mussel/or the brown mussel (P <.05), but there is no significant difference between the green and the brown ones.
3. There is a difference in crude fibre among .the 3 groups of mussel (P <.05). 4. There is a difference in calcium content among the small brown and the
green mussel, but there is neither significant difference between the small and the brown mussel nor between the brown and the green mussel.

Discussion
Fishery products and by-products such as fish meals, condensed fish solubles, fish protein concentrates, and protein from crude waste meal of crab and shrimp provide excellent sources of protein because of their higher values in protein content and quality8• Therefore, the results shown in Table 4 suggest that the analyzed mussels (Perna viridis and Modiolus metcalfei} can be considered as an alternative potential food crop capable of providing cheap animal protein, not only as feed but also as food for the masses. Their protein contents agree with the results given by Catedral9 on the green mussel (Mytilus smaragninus) and Lim 10 on the brown mussel (Modiolus metcalfei} in terms of what is considered as high percentage protein, i.e. 63.94, 70.17-77.84 and 63.44% respectively. There is no comparison among differences of protein contents in these mentioned proximate analysis due to different biotic and abiotic concern. Both growth and biological functions of animals depend on the quality of the protein as amino acid constituents rather than absolute percentage of · protein8• Ramsey 11 mentioned that inspite of lack of research, the limited data available would indicate that alternative sources cannot yet substitute fish protein

with equal efficiency. There are many reasons for their comparative lack of efficiency which go beyond differences in amino acid content of the respective protein. Therefore, this present work is only a preliminary study whose results imply that more considerable concrete works on biochemical analysis of mussel protein have to be followed if it is going to be used as feed or as supplementary diet to enchance growth for other commercial important animals such as P. monodon and Scylla serrata.
Acknowledgements
The author would like to express her appreciation toward the Southeast Asian Fisheries Development Center (SEAFDEC), Aquaculture Department, Iloilo and the Government of Thailand for their program and official-leave permission respectively. Her special thanks are for ATA staff for their administrativeassistance, to the CAL staff and particularly to her coproponent, Ms. V. Dy-Penaflordia. She is most indebted to Mr. I. Potestas who willingly and kindly supplied all the live mussel uses in the experiment, and to her adviser, Dr. L.V. Benitez for her valuable com· ments and suggestions.
References
1. Rochanaburanon, T. (1974) Rearing of some Caridea (Crustacea: decapoda) Ph.D. Thesis, Marine Biol. Dept., Liverpool Univ.
2. Kanazawa, A. (1979) Carbohydrate Metabolism in P. japonicus. Seminar presented at SEAFDEC Tigbauan. Iloilo, Phippines.
3. Tortell, P. (1977) Mussel Research Project. SEAFDEC, Mussel Research Project, 3rd Report. SEAFDEC, Aquaculture Dept., Tigbanuan, Iloilo.
4. Yap, W.G. (1978) An Experimental Assessment or the Aquaculture Potential of the Brown Mussel, Modiolus metcalfei. Aquaculture Dept., SEAFDEC, Tigbauan, Iloilo. 2nd Quarterly Research Report 11 (2): 19-23.
5. Bayne, B.L. (1976) Marine 11,fussels: Their Ecology and Physiology. Cambridge University Press, London.
6. Association of Official Analysis Chemists (1970) Official Methods of Analysis. 11th ed., The Association, Washington, D.C.
7. Lovell, R.T. (1975) Laboratory Manual For Fish Feed Analysis and Fish Nutrition Studies. Dept. of Fisheries and Allied Aquaculture, International Center of Aquacalture, Auburn Univ., .U.S.A.
8. Ramses, B.T. and William, H.I. (1975) Nutritional Evolution of Protein from Shrimp Cannery Shirmp Waste Protein. J. Agric. Food Chem. 23 (6): 1168-1171.
9. Catedral, F.F.. Dy, V. and Sayson, R. (1977) Proximate and Mineral Analysis of Mussel from Himamaylan, Negros. Unpublishecj Report, Aquaculture Dept., SEAFDEC, Tigbauan, Iloilo.
10. Lim, C. (1978) A Preliminary Study on the Evaluation of Casein, Shrimp Meal, Squid and Spirulina as Protein Sources for Penaeus monodon Post Larvae.. Aquaculture Dept., SEAFDEC, Tigbauan, Iloilo. 2nd Quarterly Research Report 2 (2): 13-18.
11. Ramsey, G.L. (1973) The Protein Situation in Fish and Feeding, Tunison Laboratory of Fish Nutrition. American Fish.