Aspects on the reproductive cycle of Donax semistriatus and Donax trunculus (Mollusca: Bivalvia) in Idku, Egypt

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1 Indian Journal of Geo-Marine Sciences Vol. ( ), March 215, pp. spects on the reproductive cycle of Donax semistriatus and Donax trunculus (Mollusca: ivalvia) in Idku, Egypt Ibrahim, R.M 1, Mohammad, S.H 2 *, Mohamed, S.Z 3 & Morsy, Z. S 1. 1 Department of Zoology, Faculty of Science, Suez Canal University, Egypt 2 Department of Zoology, Faculty of Science, Port Said University, Egypt 3 Department of Marian iology, Faculty of Science, Suez Canal University, Egypt * [ E.Mail: samya.mohammad@ymail.com ] Received; revised Present study deals with the reproductive cycle of the two clams Donax semistriatus and Donax trunculus (ivalvia: Mollusca) and it is the first in this region. Specimens of these animals were collected monthly from two sites, one of them located at waterway that discharges waste water from irrigation canal. The reproductive stages of D. semistriatus and D. trunculus were classified into: inactive, early active, late active, ripe, partially spent and spent stages. s of D. semistriatus were higher than females at both sites (male: female ratio was 1.47:1 in site 1 and 1.54:1 in site 2). Meanwhile, male D. trunculus outnumbered females in site 1 (1.38:1), and females made up a slightly higher proportion than males (1:1.13) in site 2. The sexual cycle of both species showed inactive gonad in the winter while the sexual activity was mainly detectable during spring and summer. oth species showed no signs of hermaphroditism. Temperature is found to be the factor which possibly triggers reproduction. [Keywords: Donax semistriatus, Donax trunculus, Donacidae, reproduction, Egypt.] Introduction The two clams Donax semistriatus and Donax trunculus are edible clams and very popular seafood along the Mediterranean coast of many countries. They were found in the western lgarve coast (southern Portugal) 1, in Southern Spain 2, along the Italian Southern driatic coast 3 and in lgeria 4. The two clams D. semistriatus and D. trunculus were identified among the shallow marine faunas that recorded in the littoral zone of lexandria on the Mediterranean coast of Egypt 5. The two clams were also recorded in the Mediterranean Sea water at the western area of Gamasa city and the eastern area of Port Said city, respectively 6. In literature, few studies are available about the reproduction of D. semistriatus and D. trunculus. The gametogenesis of female D. trunculus occurred in spring. fter the spawning season, females remained in a resting stage from ugust to January 3. The reproductive cycle of D. trunculus and D. semistriatus includes five stages of gonadal development: early active, late active, ripe, partially spent and spent 6. On the other hand, D. semistriatus is poorly studied. synchronous sexual cycles with continuous but partial individual spawning from pril to November in about 49 % of the D. semistriatus population were recorded 2. This work aimed to shed some light on the reproductive cycle of the two common and popular clams D. semistriatus and D. trunculus as well as the influence of the environmental factors on it. Material and Methods Study area Idku city located on the Mediterranean coast in ehira governorate, North Egypt (31 31' N Latitude and 3 3' E Longitude) The altitude of Idku was 6 m (Fig. 1). The samples were collected from two regions that exposed to different pollutions in order to see the differences in the maturity stages of the clams between the two sites. Site 1 located at waterway that discharges waste water (result from irrigation) into the sea. The other selected region (site 2) is located near other sources of pollution: harbor and Petroleum Company. Sampling total of 368 specimens of Donax sp. of different size were examined: 282 specimens of D. semistriatus and 86 specimens of D. trunculus. The samples were monthly collected from November 28 to May 21. The samples were collected at approximately 1m in depth using simple harvesting tool (hand dredge). Clams shell length was measured with a vernier caliper (up to 1. mm

2 INDIN J. MR. SCI., VOL., NO. MRCH 215 Mediterranean sea Site 1 Site 2 2- Microscopic description Microscopic observations of the two clam species revealed six stages of gonadal development (Plates 1 and 2). These are inactive stage; early active stage; late active stage; ripe stage; partially spawned stage; and spent stage as described in tables 1and 2. Egypt Fig. 1. Location of Idku city (northern Egypt) and the sampling sites (map in satellite view copied from Google maps). accuracy). Concerning evaluation of the influence of some environmental factors on the cycle, the surface water temperature was measured and samples of superficial water were taken for determination of salinity. For histological processing, the gonad were fixed in ouin s fixative, embedded in paraffin and dehydrated through an ascending series of ethyl alcohol. Sections (5 μm.) were stained with haematoxylin and eosin and the stages of gonad development were scored. Photographs were taken with a compact digital camera fixed with Microscope of Model S33PL,TECH Germany. Results Hydrographic parameters The surface temperature of the seawater was measured in the two sits. The minimum was 17 C and 18 C in February in site 1 and site 2 respectively. With the beginning of summer there was noticeable increase in temperature (25 C and 24 C in site 1 and site 2 respectively in May). Salinity varied from 36 to 4 ppm. in site 1 and 37 to 41 ppm. in site 2. Description of gonadal development 1- Visual description The gonad occupied a major part of the visceral mass as well as small portion of the foot. The testes of D. semistriatus are pale orange in color, whereas the ovaries are dark red. D. trunculus have pale orange testes and dark blue ovaries. Gametogenic cycle 1-Donax semistriatus - The reproductive cycle of female D. semistriatus showed that, during the whole cycle many individuals remain in the inactive stage (Fig. 2). The maximum percentage was in December 29 and February 21 in site 1, in site 2, it was in November 29. Specimens in early active stage appeared in September 29 and pril 21 with the percentage of 33% and 16% in site 1. Whilst in site 2, it appeared in March 21 with percentage of 16%. Individuals in late active and ripe stages were found in most months at both sites Dec-8 Dec-8 Jan-9 Jan-9 Feb-9 Mar-9 pr-9 May-9 Jun-9 Jul-9 Inactive Early active Late active Ripe Partially spent Spent ug-9 Sep-9 Feb-9 Mar-9 pr-9 May-9 Jun-9 Jul-9 ug-9 Sep-9 Oct-9 Nov-9 Dec-9 Jan-1 Feb-1 Mar-1 pr-1 May-1 Oct-9 Nov-9 Dec-9 Jan-1 Feb-1 Inactive Early active Late active Ripe Partilly spent spent Figure (2). ly variations in gonad developmental stages of female Donax semisteriatus in site 1() and site 2 (). Mar-1 pr-1 May-1

3 IRHIM et al.: SPECTS ON THE REPRODUCTIVE CYCLE OF DONX SEMISTRITUS ND DONX TRUNCULUS (MOLLUSC: IVLVI) IN IDKU, EGYPT 3 Table 1. Description of reproductive stages of gonadal development of male Donax sp. Gonad stages description of stages of the gonad Plate 1 Inactive Early active Late active Ripe Low levels of spermiogenic activity and correspondingly low levels of recognizable sex cells. Most of the gonad consists of inter follicular connective tissue. The follicle was bound by an outer follicular wall, which usually expanded when gametogenesis occurred. In the early stages of development, all follicles look similar. However, the gonads sometimes contain some developmental stages from previous spawning; in this case the sex of clams can be easily determined. Proliferation of the testes follicles became more conspicuous and interfollicular tissues were reduced. Definite spermatogonia and spermatocytes were separated from follicle cells. Spermatogonia were in close contact with the germinal epithelium. The follicles filled with primary and secondary spermatocytes. Few spermatids were detected in the center. Most of the spermatids were found to form darkly staining bands inside the follicle. Fully developed spermatozoa were seen with little amount at this stage. The follicle wall expands and the connective tissue is reduced. Spermatids radiate into the follicle lumen. The lumen contained free spermatozoa that aggregated in bands with their heads directed towards the periphery and tails towards the center. a b c d Table 2. Description of reproductive stages of gonadal development of female Donax sp. Gonad stages Inactive Early active description of stages of the gonad During the sexual rest, gonadic female follicles were very few and isolated by connective tissue. The follicles mainly contained oogonia. Determination of the follicular sex appeared difficult at this stage, except when some residual gametes in certain follicles were present. The ovarian follicles are small. Sex differentiation starts with the differentiation of the germ cells into oogonia and primary oocytes. Inter follicular tissue were noticed. Plate2 a b Late active The Follicles fully developed, filling the whole lumen. Growing appeared pear like and attached to the follicle walls by stalks. oocytes c Ripe Partially spent Spent The follicles are completely filled with ova. Growing oocytes appeared in few numbers. Growth of the packed follicles obliterates the interfollicular connective tissue. Follicles were adjacent to each other without interspace. This stage was characterized by the reduction in density of ova due to its releasing. The follicles contain few collapsed ova in addition to degenerated ova. ll ova were found to be released in this stage. The follicles contained degenerated ova only. Oogenesis started again. e d f

4 Indian Journal of Geo-Marine Sciences Vol. ( ), March 215, pp. a b sg ps sc sg sd c sd d sz sz Plate 1.Photomicrographs of the different stages of development of male Donax sp.:(a) Inactive phase; (b) Early active phase; (c) Late active phase; (d) Rip phase; sg, spermatogonia; ps, primary spermatocyte; sc, secondary spermatocyte; sd, spermatid; sz, spermatozoa. (H. and E. X 2) The percentage of ripe individuals are higher in site 2, it reached 1% in pril, June 29 and January 21. Partially spawning was recorded in May 21 with percentage of 25% in site 1 while it reached to 5% in March and July 29 in site 2. December 28 and January 29 considered being the period of complete spawning in both sits Feb-9 Mar-9 pr-9 Inactive Early active Late active Ripe May-9 Jun-9 Jul-9 ug-9 Sep-9 Oct-9 Nov-9 Dec-9 Jan-1 Feb-1 Mar-1 pr-1 May-1 - Fig (3) shows that the reproductive cycle of male D. semistriatus was approximately similar in both sites. It started in February 29. ll individuals were in early active stage. Individuals in late active stage appeared in most months, while individuals in ripe stage appeared in March 29 and May 21. Spawning was noticed in January and February 21 in site 2 only Feb-9 Mar-9 pr-9 May-9 Inactive Early active Late active Ripe Jun-9 Jul-9 ug-9 Sep-9 Oct-9 Nov-9 Dec-9 Jan-1 Feb-1 Mar-1 pr-1 May-1 Figure (3). ly variations in gonad developmental stages of male Donax semisteriatus in site 1() and site 2().

5 IRHIM et al.: SPECTS ON THE REPRODUCTIVE CYCLE OF DONX SEMISTRITUS ND DONX TRUNCULUS (MOLLUSC: IVLVI) IN IDKU, EGYPT 3 a ct b og eo og c d o go o e f o do do og eo Plate 2. Photomicrographs of the different stages of development of the female Donax sp.:(a) In active phase; (b) Early active phase; (c) Late active phase; (d) Rip phase; (e) Partially spawned phase; (f) Spent phase. ct, connective tissue; og, oogonia; eo, early oocyte; go, growing oocyte; o, ova; do, degenerated ova. (H. and E., X 2) ct 2- Donax trunculus - Histological sections of D. trunculus were carried out only in the months represented in figure (4) because of scarce of this species. In site 1, all individuals were in late active stage in pril, July 29 and pril 21. Ripening of the gonad occurred in March % and 5 % of females were partially spent and spent in the same month respectively. December 29, February and May 21 considered being the months of inactivity. In site 2, 5% of specimens were in late active stage and the remainder was in ripe stage in March 29. Spawning was maximum in pril 29. The gonads remain inactive during November and early February 29, after which a new gametogenic cycle took place. - In site 1, the reproductive cycle of D. trunculus showed that males were in late active stage in most

6 INDIN J. MR. SCI., VOL., NO. MRCH pr-9 Mar-9 Inactive Late active Ripe Partially spent spent May-9 pr-9 Jun-9 May-9 Jul-9 Jun-9 ug-9 Sep-9 Oct-9 Nov-9 Dec-9 Jan-1 Inactive Late active Ripe Spent Jul-9 ug-9 Sep-9 Oct-9 Figure (4) ly variations in gonad developmental stages of female Donax trunculus in site 1 () and site 2 () during the period of study. months (Fig. 5). Individuals in ripe stage were only recorded in May 21 with the percentage of 5%. Specimens in spent stage were recorded in February 29. The gonads were inactive in October, November and December 29. Concerning site 2, all collected specimens were in late active stage Jan-9 Feb-9 Mar-9 pr-9 May-9 Jun-9 Jul-9 ug-9 Sep-9 Oct-9 Nov-9 Inactive Late active Ripe Nov-9 Dec-9 Dec-9 Feb-1 Jan-1 Jan-1 Mar-1 Feb-1 Feb-1 Mar-1 pr-1 Mar-1 pr-1 May-1 pr-1 May-1 Synchronization in gametogenic phases The gametogenic cycles of males and females D. semistriatus showed synchronization in both sites (Fig. 6 and 7). Sex ratio Donax semistriatus The proportion of male to female in D. semistriatus varied monthly in both sites. s of D. semistriatus, are higher than females (male: female ratio was 1.47:1 in site 1 and 1.54:1 in site 2) (Fig. 8). For all size classes, males dominated females except for the largest clams in site 2 (Fig. 9). Donax trunculus This species is found with little number in each month. s of D. trunculus outnumbered females in site 1 (male: female ratio was 1.38:1). In site 2 females made up a slightly higher proportion than males (male: female ratio was 1:1.13) (Fig. 1). Concerning size classes in site 1, it was found that males dominated females except at two size classes ( and ). In site 2 the ratio was equal with slight increment of females at the size class (Fig. 11 ). Recruitment Recruits of D. semistriatus were collected from sediment at the selected sites during the studied period as shown in Table 2. The table showed that the recruits were collected only in the three months Jun, July and November 29. The maximum occurrence was in July 29 in site 1. Length of the collected spat reached to 6.2 mm. Juveniles of D. trunculus were not found in the dredged sediment. Table 3. Pattern of occurrence of Donax semistriatus recruits in the studied sites Feb-9 Mar-9 pr-9 May-9 Jun-9 Jul-9 ug-9 Late active Sep-9 Oct-9 Nov-9 Dec-9 Jan-1 Feb-1 Mar-1 pr-1 May-1 Site 1 Site 2 Jun-9-4 July Nov-9-1 Figure (5) ly variations in gonad developmental stages of male Donax trunculus in site 1() and site 2() during the period of study.

7 IRHIM et al.: SPECTS ON THE REPRODUCTIVE CYCLE OF DONX SEMISTRITUS ND DONX TRUNCULUS (MOLLUSC: IVLVI) IN IDKU, EGYPT 3 Inactive Early active Dec-8 Jan-9 Feb-9 Mar-9 pr-9 May-9 Jun-9 Jul-9 ug-9 Sep-9 Oct-9 Nov-9 Dec-9 Jan-1 Feb-1 Mar-1 pr-1 May-1 Dec-8 Jan-9 Feb-9 Mar-9 pr-9 May-9 Jun-9 Jul-9 ug-9 Sep-9 Oct-9 Nov-9 Dec-9 Jan-1 Feb-1 Mar-1 pr-1 May-1 Late active Ripe Dec-8 Jan-9 Feb-9 Mar-9 pr-9 May-9 Jun-9 Jul-9 ug-9 Sep-9 Oct-9 Nov-9 Dec-9 Jan-1 Feb-1 Mar-1 pr-1 May Dec-8 Jan-9 Feb-9 Mar-9 pr-9 May-9 Jun-9 Jul-9 ug-9 Sep-9 Oct-9 Nov-9 Dec-9 Jan-1 Feb-1 Mar-1 pr-1 May-1 Figure (6) Synchronization between male and female Donax semistriatus for different maturity stages in site1. In active Early active Dec-8 Jan-9 Feb-9 Mar-9 pr-9 May-9 Jun-9 Jul-9 ug-9 Sep-9 Oct-9 Nov-9 Dec-9 Jan-1 Feb-1 Mar-1 pr-1 May-1 Dec-8 Jan-9 Feb-9 Mar-9 pr-9 May-9 Jun-9 Jul-9 ug-9 Sep-9 Oct-9 Nov-9 Dec-9 Jan-1 Feb-1 Mar-1 pr-1 May-1 Late active Ripe Dec-8 Jan-9 Feb-9 Mar-9 pr-9 May-9 Jun-9 Jul-9 ug-9 Sep-9 Oct-9 Nov-9 Dec-9 Jan-1 Feb-1 Mar-1 pr-1 May-1 Dec-8 Jan-9 Feb-9 Mar-9 pr-9 May-9 Jun-9 Jul-9 ug-9 Sep-9 Oct-9 Nov-9 Dec-9 Jan-1 Feb-1 Mar-1 pr-1 May-1 Figure (7) Synchronization between male and female Donax semistriatus for different maturity stages in site2.

8 Dec-8 Jan-9 Feb-9 Mar-9 pr-9 Undiffrentiated May-9 Jun-9 Jul-9 ug-9 Sep-9 Oct-9 Nov-9 Dec-9 Jan-1 Feb-1 Mar-1 pr-1 May Dec-8 Jan-9 Feb-9 Mar-9 Undiffrentiated pr-9 May-9 Jun-9 Jul-9 ug-9 Sep-9 Oct-9 Nov-9 Dec-9 Jan-1 Feb-1 Mar-1 pr Undiffrentiated Undifferentiated Nov-8 Dec-8 Jan-9 Feb-9 Mar-9 pr-9 May-9 Jun-9 Jul-9 ug-9 Sep-9 Oct-9 Nov-9 Dec-9 Jan-1 Feb-1 Mar-1 pr-1 May-1 Dec-8 Jan-9 Feb-9 Mar-9 pr-9 May-9 Jun-9 Jul-9 ug-9 Sep-9 Oct-9 Nov-9 Dec-9 Jan-1 Feb-1 Mar-1 pr-1 May-1 Figure (8) Donax semistriatus. ly percentage occurrence of both sexes in site 1 () and site 2 (). Figure (1) Donax trunculus. ly percentage occurrence of both sexes in site 1 () and site 2 () Uniffrentiated Class size (mm) Undiffrentiated Class size (mm) Undifferentiated Undiffrentiated Class size (mm) Class size (mm) Figure (9) Donax semistriatus. Percentage occurrence of both sexes in site 1 () and site 2 () for different shell lengths. Figure (11) Donax trunculus. Percentage occurrence of both sexes in site 1 () and site 2 () for different shell lengths.

9 IRHIM et al.: SPECTS ON THE REPRODUCTIVE CYCLE OF DONX SEMISTRITUS ND DONX TRUNCULUS (MOLLUSC: IVLVI) IN IDKU, EGYPT 3 Discussion ivalves of the genus Donax are important component of the shallow-bottoms macrofauna of exposed sandy beaches 7. Donacidae are suspensionfeeders feed on suspended particulate organic matter 8. The reproductive cycle of different Donax sp. was discussed by many authors however the reproductive cycle of Donax semistriatus is poorly studied. The present work revealed that males D. semistriatus are found to outnumbered females in both sites. : female ratio was 1.47:1 in site 1 and 1.54:1 in site 2. In D. trunculus, males outnumbered females in site 1 (male: female ratio was 1.38:1). In site 2 females made up a slightly higher proportion than males (male: female ratio was 1:1.13). The sex ratio of D. semistriatus can be considered to be 1:1 2. It was found that males of D. trunculus usually made up a slightly higher proportion than females but with no significant difference from a sex ratio of 1:1 9. The environmental factors are found to influence the sex ratio of the clam 1. So, we can assume that the impact of pollution of the studied area on females by a higher degree of influence rather than males, and consequently led to their relatively decimation. This assumption previously confirmed as that the increment of males in Cerastoderma glaucum may be due to the exhausting of female owing to their continuous spawning, which made them more sensitive to pollution than males and led them to death 11. The reproductive cycle of D. semistriatus and D. trunculus showed six different maturity stages 6, 9. The result of histological examination revealed the coexistence of several stages of development in the same gonad. The coexistence of different stages has been found in different donacid species, among them, D. venustus and D. semistriatus 2 and D. denticulatus 12. Other genera (Venus verrucosa) also exhibited the same phenomenon 13. The present work showed that D. semistriatus and D. trunculus were inactive during winter while the sexual activity was mainly detectable during spring and summer. Most individuals of D. semistriatus in Southern Spain are pre-active during the winter and the main spawning period was in summer 2. lso, the gonads of Namibian D. serra were mature in summer and inactive during autumn and early winter 14. The sexual activity of D. hanleyanus at rgentinean sandy beaches was recorded during spring and summer while cytolysed specimens dominated the population in autumn and winter 15. The reproductive cycle of D. trunculus also showed that gametogenesis occurred in spring in females which remained in a resting stage from ugust to January 3. Generally, the present work proved that there were no differences in the reproductive cycle of the two clams D. semistriatus and D. trunculus in both sites. D. semistriatus and D. trunculus showed no signs of sex hermaphroditism 6, 9. The present histological study of D. semistriatus showed synchronous sexual cycles. It was found that D. semistriatus at Southern Spain had asynchronous sexual cycles 2. In the present work, Recruits of juveniles of D. semistriatus were collected from sediment in the three months Jun, July and November 29. The maximum occurrence was in July 29 in site 1 and this result support the achieved histological investigation. The recruits of D. venustus was collected from sediment with less intense during most of the year with a peak in September and these data agree with those obtained in the histological study of the gametogenic cycle 2. While the recruitment period of D. hanleyanus extended over the period February to May 16. The present study showed that recruits of D. trunculus were not found in the dredged sediment, however the main period of larval recruitment of D. trunculus on the French tlantic coast extends over the period from July to September 17. The effect of environmental factors on reproduction was discussed by many authors. The reproductive cycle of Namibian D. serra was related to the monthly mean sea surface temperature cycle 14. lso gametogenic cycle of D. hanleyanus correlated significantly with sea surface temperature 15. The present work proved that the gradual increases in temperature coincident with the development of the gonad so the period of sexual activity was mainly detectable during spring and summer seasons. Salinity fluctuation may be happened due to climatic factors such as heavy rains during rainy seasons or as a result of discharge of fresh water that result from agricultural works into the sea. In the present work there were no obvious changes in salinity at the selected sites. Changes in salinity are found to be the major factor which triggers

10 INDIN J. MR. SCI., VOL., NO. MRCH 215 reproduction and temperature was not at all a factor governs reproduction 1. Conclusion D. semistriatus and D. trunculus did not show any signs of sex hermaphroditism. The reproductive stages of D. semistriatus and D. trunculus were classified into inactive, early active, late active, ripe, partially spent and spent stages. There was a gradual increase in temperature coincident with the development of the gonad. Sexual activity of both species was mainly detectable during spring and summer. Recruits of juveniles of D. semistriatus were collected from sediment in three months: Jun, July and November 29, the maximum occurrence was in July 29. The gonads were inactive in the winter. s outnumbered females, while there was slight increase of females D. trunculus in site 2. References 1 Gaspar, M.., Santos, M. N., Vasconcelos, P. and Monteiro, C. C, Shell morphometric relationships of the most common bivalve species (Mollusca: ivalvia) of the lgarve coast (southern Portugal), Hydrobiologia, 477 (22), Tirado, C. and Salas, C., Reproduction of Donax venustus Poli 1795, Donax semistriatus Poli 1795 and Intermediate Morphotypes (ivalvia: Donacidae) in the Littoral of Ma laga (Southern Spain), Marine Ecology, 2 (1999), Manca Zeichen, M., gnesi, S., Mariani,., Maccaroni,. and rdizzone G. D., iology and Population Dynamics of Donax trunculus L. (ivalvia: Donacidae) in the South driatic Coast (Italy), Estuarine, Coastal and Shelf Science, 54 (22), elabed, S. and Soltani, N., cute toxicity of cadmium on Donax trunculus: acetylcholinesterase, glutathione S- transferase activities and pattern of recovery, European Journal of Experimental iology, 3(213), Frihy, O. E., Iskander M. M. and adr.., Effects of shoreline and bedrock irregularities on the morphodynamics of the lexandria coast littoral cell, Egypt, Geo-Mar Lett., 24 (24), El-refaey, sh. R., iological studies on some bivalves (bivalvia : mollusca) inhabiting the Mediterranean sea coast, north of Egypt, Ph.D. Thesis, Mansoura university, Faculty of science, Department of zoology, 26 7 nsell. D., The biology of the genus Donax. In Sandy beaches as ecosystems (McLachlan,. and Erasmus, T., eds). Junk Publishers, The Hague, 1983 pp Wade,.., Notes on the ecology of Donax denticulatus (Linne ), Proc. Gulf. Carib. Fish. Inst, (17 nn. Sess.) (1964), li, E. M, Mohammed, S. H., Mohamed, S. Z. and amer, M.., Reproductive cycle of Donax trunculus (Mollusca: ivalvia) in Port Said, Mediterranean Coast, Egypt, Mansoura Journal of biology, 36 (29), run,. U., Gametogenic cycle in Villorita cyprinoides and the influence of salinity, CL ioflux, 2 (29), Mohammad, S. H., elal,.. and El-groudy, N.., Study on Cerastoderma glaucum (ruguière, 1789) s a iomonitor spect of Oil Pollution in Lake Timsah, Suez Canal, Egypt, CTRIN, 4 (29), Rojas,. V., Reproductive biology of the tropical clam Donax denticulatus in eastern Venezuela, Carib. J. Sci., 21 (1985), Tirado, C., Salas, C. and Marquez, I., Reproduction of Venus verrucosa L., 1758 (ivalvia: Veneridae) in the littoral of Malaga (southern Spain), Fisheries Research, 63 (23), Laudien, J., rey, T. and rntz, W.E., Reproduction and recruitment Pattern of the surf clam Donax serra (ivalvia, Donacidae) from two Namibian sandy beaches, South frican Journal of marine Science, 23 (21), Herrmann, M., arreira, C..R., rntz, W.E., Laudien, J. and Penchaszadeh, P. E., Testing the habitat harshness hypothesis: The reproductive biology of the wedge clam Donax hanleyanus (ivalvia: Donacidae) from three rgentinean sandy beaches with contrasting morphodynamic, Journal of Molluscan Studies, 76 (21), Defeo, O. and lava,. D., Effects of human activities on long-term trends in sandy beach populations: the wedge clam Donax hanleyanus in Uruguay, marine ecology progress series. 123 (1995), nsell,. D. and Lagardere, F., Observations on the iology of Donax trunculus and D. vittatus at Ile d'oleron (French tlantic Coast), Marine iology,57 (198) 287-3