studies which are of interest in the wider context of the monitoring or sediments for other pollutants. The advantages of radioactive studies have been described. Some of the questions which need to be answered before sediment monitoring data can be interpreted meaning- fully are raised and it has suggested how radionuclide studies may be helpful in answering these questions.

Chester, K. & Hughes, M. J. (1967). A chemical technique for the separation of ferromanganese minerals, carbonate minerals and adsorbed trace metals from pelagic sediments. Chem. GeoL, 2, 249-262.

Duursma, E. K. & Bosch, C. J. (1970). Theoretical, experimental and field studies concerning diffusion of radioisotopes in sediments and suspended solid particles of the sea. Neth. J. sea Res., 4,395--469.

Marine Pollution Bulletin

Goldberg, E. D. et al. (1971). Marine Chemistry. In Radioactivity in the Marine Environment pp. 137-146. National Academy of Sciences , National Research Council, Washington, DC.

Hetherington, J. A. (1976). The behaviour of plutonium nuclides in the Irish Sea. in Environmental Toxicity o f Aquatic Radionuclides: Models and Mechanisms, M. W. Miller and J. N. Stannard (eds.) pp. 81-106. Ann Arbor Science, Ann Arbor.

Hetherington, J. A. & Jefferies, D. F. (1974). The distribution of some fission product radionuclides in sea and estuarine sediments. Neth. J. sea Res., 8,319-338.

Jefferies, D. F. (1968). Fission product radionuclides in sediments from the north-east Irish Sea. Helgoldnder wiss. Meeresunters., 17, 280-290.

Jefferies, D. F. et al. (1973). Distribution of caesium-137 in British coastal waters. Mar. Pollut. Bull., 4,118-122.

Presley, B. J. et al. (1972). Early diagenesis in a reducing fjord, Saanicb Inlet, B.C. I1. Trace element distribution in interstitial water and sediment. Geochim. Cosmochim. Acta, 36, 1073-1090.

Walkley, A. (1947). A critical examination of a rapid method for determining organic carbon in soils. Soil Sci., 63,251-263.

Marine Pollution Bulletin, Vol. 9, pp. 106-108 © Pergamon Press Ltd. 1978. Printed in Great Britain

0025 - 326X/78/0401-0106502.00/0

Zinc Content in Otoliths of Mackerel from the Aegean C. PAPADOPOULOU, G. D. KANIAS* and ELLI MORAITOPOULOU KASSIMATI§ *Department of Chemistry, Nuclear Research Centre "Democritos" Agia Paraskevi A ttikis, Athens Greece §Greek Institute of Oceanographic and Fishing Research, Athens, Greece

The zinc content in otoliths of the mackerel (Scomber ]aponicus colias) has been determined by instrumental neutron activation analysis. Six groups each of twelve specimens of the same age selected from three areas of the Aegean sea have been analysed. The zinc content was found to be a linear function of the age and body length.

The marine environment is characterized by relatively constant chemical and physical conditions. Therefore the marine organisms adapted to these conditions would hardly accept sudden changes in their environment caused by pollutants. The presence of unusual new substances and trace elements in high level in seawater presents a problem for the development and survival of the marine population.

In order to reveal the extent of the damage caused to the organisms from the effects of pollutants, a systematic study of the population dynamic parameters (i.e. growth rate, mortality etc.) or the behaviour pattern should be undertaken for several life cycles. Zinc is a constituent of many metalloenzymes, proteins and structural cellular components, but it is also listed among the high potential polluting elements (Bowen, 1966). High concentrations of zinc in the sea may result from the discharge of industrial wastes from mining, electroplating and synthetic fibre production (Bryan, 1971). In addition to this, the radionuclide of zinc (65Zn) derived from radio- active waste discharge and fallout in the sea has also been detected in various organisms (Folsom et al., 1963;

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Robertson et al., 1968; McCauley, 1971). Studies on the zinc content in marine species have been reported by Vinogradov (1953) and Goldberg (1963).

The research work on the chemical composition of skeletal formations is concerned mostly with the bones of the fish (Vinogradov, 1953; Saiki, 1968; Papadopoulou et ak, 1972). Among the skeletal formations of fish, the otoliths are of special importance because of their role in the balance, the movement and therefore the survival of fish population. To the best of our knowledge data on the trace element content of the fish otoliths are limited only to the work dealing with the determination of certain oxides given by Vinogradov (1953). The present work deals with the determination of zinc content in otoliths of the fish Scomber japonicus colias and the correlation of this content with the age and total body length variation. This is a pseudo-migratory species and has a commercial value for Greece. It is met in schools from March to October and it disappears during the winter period. It is caught in large quantities especially in the months of July, August and September. It takes its food (plankton and small fishes) from the bottom of the sea to the surface because of its vertical movements and from the examination of stomach contents it was found that this species feeds preferably on crustaceans especially Amphipoda, Isopoda, Stomatopoda, Copepoda, Decapoda and small fish. Therefore the features mentioned above led to the selection of this species for the study of the transport of pollutants for Greek waters through the food chain to man. The

Volume 9 / N u m b e r 4/April 1978

analytical method applied was neutron activation of the samples.

y-spectrometry after

Experimental

Sampling

The fish samples were collected from three areas of the Aegean sea: Dodecanese, Cyclades islands, Petalion Gulf (Fig. 1). These sampling areas are among the most important fishing quarters of Scomber from Greek waters and are considered as unpolluted areas of the Aegean sea. The collection was carried out in a seven month period from March to October 1961. Seawater salinity and temperature of the sampling areas was as follows:

Sampling Area S %o Temperature (°C)

Dodecanese 38-39 12-24 Cyclades Islands 39 13-25 Petalion Gulf 38-39 12-24

Fish samples were grouped together according to the fishing areas, age and total body length.

Fish otoliths used for the analytical work were care- fully removed, and age determination and total body length were recorded for each individual. Twelve animals were used for the zinc analysis from each group. No one-year-old fish were caught in the Dodecanese sampling area and no two or three year-old fish from the area of Petalion Gulf. One hundred and eighty individuals of Scomber japonicus colias were used for the determination of zinc in the otoliths.

Apparatus

A Ge(Li) detector of 37 cm 3 connected with an Inter- technique 4000 channel pulse-height analyser (Model Didac 4000) was used for the determination of zinc in otoliths.

Procedure

The otoliths were placed in quartz tubes and dried at 65°C for 48 h. An aliquot (0.2 ml) of the zinc standard solution was also placed in identical quartz tubes. Samples and standards were irradiated together in the Nuclear Research Centre 'Democritos' reactor at a thermal flux 2.2 × 1013 n.cm -2 s -l for 100 h. 'After a 50 day cooling-time the y-radiation spectrum of the 65Zn was measured by means of the multi-channel analyser.

: i/: ' i "¸ /:i 7`: ......

r r .

Fig. 1 Sampling areas from the Aegean sea.

Results and Discussion The results obtained from this study are listed in

Table 1. Figure 5 shows the variation of zinc content in the otoliths versus age for all three sampling areas. The content of zinc in the otoliths of Scomber varies from about 7 to 60 ppm (Table 1). No comparable data exist in the literature.

The fact that organs and bones of marine animals are storage sites for certain metals even under normal conditions (Bryan, 1971) led us to study systematically the role which fish otoliths play in the storage activity especially for the biologically essential trace elements. It can be seen from Fig. 5 that the variation of the zinc concentration seems to follow the same general pattern in the three areas.

The body length and age were therefore plotted against the zinc content in otoliths of the fish from the areas studied (Figs 2, 3 and 4). The plots of Figs 3 and 4 are linear with a negative slope while in Fig. 2 only the tail of the curve varies linearly but the slope is zero. In the last case the experimental points, marked with their

T A B L E 1 Mean values* of body length (Lz) of Scomberjaponicas colias and zinc content (ppm in dry matter)

in the otoliths in relation to age in samples collected from Aegean sea areas.

Sampling areas Parameters 1 2

LI (cm) - - 26.6 Dodecanese Zn (ppm) - - 35._+_9.5

Petalion Gulf LI (cm) 20.0 Zn (ppm) 164-9.5

Cyclades Islands LI (cm) 24.6 27.0 Zn (ppm) 43_+..6.5 67_+._26

Age (years)

3 4 5 6

28.3 29.9 31.3 33.2 33+6 .3 27_.+_.10 12_.+_3.5 7.4_.+..1.6

- - 30.0 32.3 33.7 - - 12._+_4.4 10_+_4 7.24-1.8

28.2 30.1 31.8 36.0 20._+_7.4 21 _+_ 11 214-10 204-9

*With s tandard deviation from 12 samples.

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Marine Pollution Bulletin

Age - years Age - years 2 4 6 1 3 5

1000 il 16 I T !I;Oo O % I

" i i I [ i t i I I I J a , I A J I J LI ~ cm 20 2 5 30

Fig. 2 Correlation of the body length (Lt) and age with the zinc Lt ,-cm content in otoliths of Scomberjaponicus colias collected from Fig. 4 Correlation of the body length (Lt) and age with the zinc Cyclades island area. content in otoliths of Scomber japonicus colias collected from

Petalion gulf area.

Age . yeors I i 2 4 6 I , ! ~Cyclodes islands

IOodecGnese

50 E I ~ DPe to l i on Gulf o.

N

10 Fig. 5 Variation of the Zn content in otoliths of the Scomberjaponicus colias vs the age from three representative areas of the Aegean

2" 6 ' ' ' 3" 0 . . . . . . t sea. 34 38 L~ --cm

Fig. 3 Correlation of the body length (Lt) and age with the zinc content in otoliths of Scomber japonicus colias collected from Dodecanese sea area.

standard deviation, show that the uncertainty in tracing the initial part of the curve is important but that the zinc values are double and even higher in the young and small fish than in fish more than three years old, which have a constant zinc content. The general conclusion from these figures is that the zinc content in otoliths is inversely proportional to the age and length of Scomber japonicus colias.

The decrease of the metal concentration in the older individuals could be attributed to metabolic factor differences, to food intake or larger fish, or to fish mgvement. These are possibly connected with the pecularities encountered in Fig. 5. The analytical and biometrical results of this work seem to be connected with the normal development and growth of certain fish populations. Therefore, the correlation of zinc content in otolith with morphological or biometrical parameters could be used for detecting at the right moment the harmful effects caused by this element to the organism provided this correlation is valid in many species.

It is to be noted that a decrease of the zinc content in the tissues of Platychthyes flesus with the age was found by Hardisty et al. (1974a). Comparisons of the rates of growth, feeding habits and heavy metal levels of flounders from the Severn estuary and Bristol channel have been made by Hardisty et al. (1974b). In this work a decrease was found in zinc concentration with the age in the fish tissues. Constant or decreasing concentrations of zinc vs total body weight in white muscle of two fish species

was reported by Cross et aL (1973). In order to under- stand the process which regulates the trace metal concentration in skeletal formations a more extended study of the metal content in the tissues and organs of the fish is needed.

Bowen, H. J. M. (1966). Trace Elements in Biochemistry. Academic Press, London.

Bryan, G. W. (1971). The effects of heavy metals (other than mercury) on marine and estuarine organisms. Proc. R. Sac. Land. B, 1"/7, 389--410.

Cross, F. A., Hardy, L. H., Jones, N. Y. & Barber, R. T. (1973). Relation between total body weight and concentrations of mangan- ese, iron, copper, zinc and mercury in white muscle of bluefish (Pomatotus saltatrix) and a batlyl-demersal fish (.4 ntimora rostrata). J. Fish. Res. BdCan., 30, 1287-1291.

Folsom, T. R., Young, D. R., Jonson, G. N. & Pillai, K. C. (1963). Manganese-54 and zinc-65 in coastal organisms of California. Nature (L and.), .200, 327 -329.

Goldberg, E. (1965). Review of trace element concentrations in marine organisms. Puerto Rico Nuclear Center, Puerto Rico.

Hardisty, M. W., Huggins, R. J., Kartar, S. & Sainsbury, M. (1974a). Ecological implications of heavy metal concentrations in fish from the Severn Estuary. Mar. Pollut. Bull,, 5, 12-15.

Hardisty, M. W., Kartar, S. & Sainsbury, M. (1974b). Dietary habits and heavy metal concentration in fish from the Severn Estuary and Bristol Channel. Mar. Pollut. Bull,, 5, 61-63.

McCauley, J. E. (1971). Ecological studies of radioactivity in the Columbia River estuary and adjacent Pacific Ocean. Oregon State University Progress Report, Corvallis, Oregon.

Papadopoulou, C. P., Hadjistelios, I. & Grimanis, A. P. (1972). Schedule of elements distribution in the main organs of fish PageHus erythrinus. Greek Limnol. Oceanogr., X1,601-608.

Robertson, D. E., Rancitelli, A. L. & Perkins, W. R. (1968). Multi- element analysis of seawater, marine organisms and sediments by neutron activation analysis without chemical separation. Batelle Memorial Institute Report BNWL SA-1776. Rev. Pacific Northwest Lab. Richland Washington.

Saiki, M. (1968). Marine radioecological studies in Japan. Seminar on Marine Radioecology. Cherbourg, 3-6 December 1968. pp. 77-84.

Vinogradov, A. P. (1953). The Elementary Composition of Marine Organisms. Sears Foundation for Marine Research, Yale University, New Haven, Connecticut.

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