FIRST INFORMATION ON THE REPRODUCTIVE BIOLOGY OF THE BLUEFIN TUNA (THUNNUS THYNNUS) IN THE EASTERN MEDITERRANEAN

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1 SCRS/2003/124 Col. Vol. Sci. Pap. ICCAT, 56(3): (2004) FIRST INFORMATION ON THE REPRODUCTIVE BIOLOGY OF THE BLUEFIN TUNA (THUNNUS THYNNUS) IN THE EASTERN MEDITERRANEAN S. Karakulak 1, I. Oray 1, A. Corriero 2, A. Aprea 2, D. Spedicato 2, D. Zubani 2, N. Santamaria 2, G. De Metrio 2. SUMMARY The presence of spawning bluefin tuna (Thunnus thynnus) in the Levantine Sea during late May-early June 2003 is reported. This finding assures that bluefin tuna spawns in the eastern Mediterranean, where spawning can occur about one month earlier than reported for other Mediterranean spawning areas. RÉSUMÉ Le présent document décrit la présence de thons rouges (Thunnus thynnus) en état de frai dans la mer du Levant à partir de la fin du mois de mai jusqu au début du mois de juin Cette constatation permet d affirmer que le thon rouge fraie à l est de la Méditerranée, où le frai peut se produire environ un mois plus tôt que prévu dans d autres zones de frai méditerranéennes. RESUMEN Se informa acerca de la presencia de atún rojo reproductor (Thunnus thynnus) en el Mar de Levante durante finales de mayo-principios de junio de Este descubrimiento certifica que el atún rojo desova en el Mediterráneo oriental, donde el desove puede tener lugar un mes antes de lo establecido para otras zonas de desove del Mediterráneo. KEYWORDS Bluefin tuna, Reproduction, Eastern Mediterranean 1 Faculty of Fisheries - Istanbul University (Turkey). 2 Department of Animal Health and Well-being - University of Bari (Italy). 1158

2 1 Introduction It is known that the eastern Atlantic bluefin tuna (Thunnus thynnus) spawns in the Mediterranean during June - July (Susca et al., 2001; Medina et al., 2002; Corriero et al., 2003). Three main spawning areas located in the Western and Central Mediterranean are known since many years for the Eastern Atlantic bluefin tuna: waters around Balearic Islands, waters around Malta Island, and South Tyrrenhian Sea. In these spawning grounds, the presence of females with hydrated oocytes and postovulatory follicles or bluefin larvae, have been recently reported (Nishida et al., 1998; Medina et al., 2002; Corriero et al., 2003). On the contrary, the information about the reproductive biology of the bluefin tuna in the eastern Mediterranean are scarce and, for the Black Sea, limited to some findings of eggs and larvae (Vodyanitsky, 1936) and to the observation of the presence of some fish with ripe gonads in July-August (Akyüz and Artüz, 1957). More recently, few larvae were found by Piccinetti and Piccinetti Manfrin (1994) and Nishida et al. (1998) in the Levantine Sea, while findings of Piccinetti et al. (1995), Piccinetti et al. (1997) and Oray and Karakulak (1998) did not allow confirming the presence of a spawning area in the eastern Mediterranean. 2 Material and methods Gonads from 50 bluefin tuna specimens (27 females and 23 males) were collected from May 20 th to June 6 th 2003 aboard purse seiners operating in the Levantine Sea (Figure 1). Biometrical data, geographical coordinates of capture and sea surface temperature (SST) were recorded. The size frequency distribution of the samples specimens is shown in Figure 2. Ovary slices were fixed onboard in Bouin s solution and transferred in Italy at the laboratory of Bari University where they were embedded in paraffin wax. Sections (5 µm thick) were stained with haematoxylin - eosin. Oocyte developmental stages were classified according to Corriero et al. (2003). 3 Results and conclusions The results are summarized in Table 1. Twenty of 27 (74%) females would have spawned in a short time or had just spawned, as evidenced from the presence of post-vitellogenic oocytes or post-ovulatory follicles (Figures 3a, b). Four females had advanced yolked oocytes, but no sign of spawning and only three females had ceased their reproductive activity as demonstrated by the presence of extensive atresia of vitellogenic oocytes (Figure 3c). All the males had mature testes with both seminipherous tubules and main sperm duct (vas deferens) filled with spermatozoa (Figure 3d). The SSTs recorded during the sampling campaign ranged between 22.5 and 24.9 C, in agreement with Schaefer (1998) and Block et al. (2001) who reported that tuna-species spawn mainly in SSTs ranging between 24 and 26 C. These findings assure that bluefin tuna spawns in the eastern Mediterranean, where spawning can occur about one month earlier than reported for other Mediterranean spawning areas. The low number of eggs and larvae obtained during campaigns carried out in July-August (Piccinetti and Piccinetti Manfrin, 1994; Piccinetti et al., 1997; Nishida et al., 1998), could be explained by the early spawning occurring in the Eastern Mediterranean. 4 Acknowledgements We are grateful to the Ministry of Agriculture of Turkey and of Turkish Republic of Northern Cyprus, the Turkish Bluefin Tuna Farmers Association and the Turkish fish farming AKUA-DEM (Istanbul, Turkey) and DARDANEL (Istanbul, Turkey), for their valuable support. We wish also to thank Dr. José Louis Cort (IEO Santander, Spain) and Didem Gokturk (Istanbul University, Turkey) for their precious assistance in field, and Dr. Michele Deflorio, Mrs. Annunziata Marinelli, Mr. Vincenzo Pesola, and Mr. Martino Cacucci (Bari University, Italy) for their technical help. This work was financially supported by contract number Q5RS from the European Commission. 5 References AKYÜZ E. and I. Artüz Some observations on the biology of tuna (Thunnus thynnus) caught in Turkish waters. Conseil général des pêches pour la Médeterranée. Document Techniques. Rome. 14,

3 BLOCK B.A., H. Dewar, S.A. Blackwell, D. Williams, E.D. Prince, C.J. Farwell, A. Boustany, S.L.O. Teo, A. Seitz, A. Walli, F. Douglas Migratory movements, depth preferences, and thermal biology of Atlantic bluefin tuna. Science 293, CORRIERO A., S. Desantis, M. Deflorio, F. Acone, C.R. Bridges, J.M. de la Serna, P. Megalofonou, G. De Metrio Histological investigation on the ovarian cycle of the eastern Atlantic bluefin tuna (Thunnus thynnus L.). Journal of Fish Biology 63, MEDINA A., F.J. Abascal, C. Megina, A. García Stereological assessment of the reproductive status of female Atlantic northern bluefin tuna during migration to Mediterranean spawning grounds through the Strait of Gibraltar. Journal of Fish Biology 60, NISHIDA T., S. Tsuji, K. Segawa Spatial data analyses of Atlantic bluefin tuna larval surveys in the 1994 ICCAT BYP. ICCAT. Collective Volume of Scientific Papers 48, ORAY, I.K. and S. Karakulak Investigations on the reproductive biology of bluefin tuna (Thunnus thynnus, L. 1758) in the North Aegean Sea. ICCAT. Collective Volume of Scientific Papers 49, PICCINETTI C. and G. Piccinetti Manfrin Distribution des larves de Thonidés en Méditerranée. FAO Fisheries Report 494, 186, 206. PICCINETTI-MANFRIN, G., G. Marano, G. De Metrio, G. Piccinetti An attempt to find eggs and larvae of bluefin tuna (Thunnus thynnus) in the Black Sea. ICCAT. Collective Volume of Scientific Papers 44, PICCINETTI G., G. Piccinetti-Manfrin, S. Soro Résultats d une campagne de recherché sur les larves de thonidés en Méditerranée. ICCAT. Collective Volume of Scientific Papers 46, SCHAEFER K.M Reproductive biology of yellowfin tuna (Thunnus albacares) in the eastern Pacific Ocean. Bulletin Inter-American Tropical Tuna Commission 21, SUSCA V., A. Corriero, C.R. Bridges, G. De Metrio Study of the sexual maturity of female bluefin tuna: purification and partial characterization of vitellogenin and its use in an enzyme-linked immunosorbent assay. Journal of Fish Biology 58, VODYANITSKY V.A Observations on pelagic eggs of epy Black Sea fishes. Travaux de la Station Biologique de Sebastopol 5, (in Russian). Table 1. Histological classification of the bluefin tuna gonads No of SST ( C) FL (cm) Weight (kg) GSI specimens min max min max min max min max Females n.a Males n.a. n.a n.a. n.a. = not available Histological classification Spawning (presence of postvitellogenic oocytes and/or post-ovulatory follicles) Non-spawning (late vitellogenic oocyte; no sign of spawning) Inactive (major atresia of vitellogenic follicles) Spawning (seminipherous tubules and main sperm duct filled with spermatozoa) 1160

4 Figure 1. Geographical location of the bluefin tuna catches (circles) Females 23 Males Number of specimens FL (cm) Figure 2. Size frequency distribution of the sampled bluefin tuna. 1161

5 Figure 3. Gonads form bluefin tuna captured in the Levantine Sea. Haematoxylin-eosin staining. (a) Hydrated oocytes in a spawning fish (bar = 300 µm). (b) Ovary from an active spawning specimen with migratory nucleus oocytes and post-ovulatory follicles (bar = 300 µm). Inset: higher magnification of part of (b) showing a postovulatory follicles (bar = 50 µm). (c) Ovary from an inactive fish showing the most advanced oocytes at lipid stage and both α and β atresia of vitellogenic follicles (bar = 150 µm). (d) Testis from a spawning male: seminipherous tubules and main sperm duct are filled with spermatozoa. (bar = 600 µm). Arrow, post-ovulatory follicle; asterisk, α atretic vitellogenic follicles; double asterisk, β atretic vitellogenic follicle; ev, early vitellogenic oocyte; h, hydrated oocyte; l, lipid-stage oocyte; lv, late vitellogenic oocyte; md, main sperm duct; mn, migratory nucleus-stage oocyte; p, perinucleolar-stage oocyte; st, seminipherous tubule. 1162