ORIGINAL PAPER A. Russo á F. Angelini á R. Carotenuto á F.M. Guarino C. Falugi á C. Campanella Spermatogenesis in some Antarctic teleosts from the Ross Sea: histological organisation of the testis and localisation of bFGF Accepted: 24 October 1999 Abstract Testis structure and spermatogenetic activity were studied in two Antarctic teleostean species, Chionodraco hamatus and Trematomus bernacchii, cap- tured during the austral summer in the Ross Sea. The specimens of C. hamatus showed full reproductive activity but, the spermatogenetic cycle being over, only spermatogonia and Sertoli cells were present in the seminiferous tubules whereas the lumina were full of sperm. By contrast, the specimens of T. bernacchii were in the stage of spermatogenetical recrudescence, having not yet entered the reproductive period. In this species, the seminiferous tubules were devoid of lumen and full of spermatogonial cysts, showing some mitoses. Many tubules contained cysts of meiotic spermatocytes I and, in one case only, small cysts of spermatocytes II. The ®nal stages of spermatogenesis were lacking, presumably occurring later, in autumn/winter. The immunocyto- chemical tests aimed at identifying bFGF and FGFR1 revealed a positive reaction both in Sertoli cells and spermatogonia in the C. hamatus specimens, indicating that this species was ready to start a new spermatoge- netic cycle. The weak reaction in the specimens of T. bernacchii suggests that, in this species, the stage of cell division was over and that of meiosis and dieren- tiation was starting. These data indicate that Antarctic ®sh have an opportunistic spermatogenetic cycle. Introduction In teleosts, testis organisation varies depending on spermatogonia distribution in the seminiferous tubules (Grier et al. 1980). In the unrestricted type of tubular testis, typical of Salmoniformes, Cypriniformes and Perciformes, spermatogonia are present throughout the tubule walls where, on completion of spermatogenesis, only associations of Sertoli cells and staminal germ cells are found. In the restricted type of lobular testis, typical of Atheriniformes, all spermatogonia are con®ned to the distal end of the lobules and, on completion of sper- matogenesis, the lobule walls are constituted only by Sertoli cells (Grier 1981). In both testicular types, in- terstitial Leydig cells are found in the intertubular spaces, their size and number varying in relation to the spermatogenetic cycle and the steroidogenetic function (Grier 1981; Borg 1994). Around the tubule walls, lobule boundary cells are organised as a discontinuous pe- ripheral layer where they probably exert a contractile function, similar to the myoid cells of mammalian testes (Dym and Fawcett 1970). In teleosts, reproduction presents a considerable va- riety of strategies aimed at ensuring reproductive suc- cess. Generally, spermatogenesis has an annual cycle. However, timing of gametogenesis, spermiation and sexual rest varies remarkably from species to species, being regulated by several abiotic and biotic (ultimate) environmental factors, the most important of which are photoperiod, food supply and temperature (de Vlaming 1974; Scott 1979; Nash 1999). By contrast, tropical species and some typical temperate species (i.e. a number of cyprinids) show continuous spermatogenesis throu- ghout the year, behaving as potential continuous breeders if suitable environmental conditions are main- tained (de Vlaming 1975; Billard et al. 1978). Growth factors, such as IGF, FGF and its receptor FGFR1, along with environmental and hormonal fac- tors (gonadotropins and sexual steroids), have crucial roles in the regulation of the spermatogenetic cycles in Polar Biol (2000) 23: 279±287 Ó Springer-Verlag 2000 A. Russo á F. Angelini (&) á R. Carotenuto F.M. Guarino á C. Falugi á C. Campanella Dipartimento di Biologia Evolutiva e Comparata, University of Naples Federico II, via Mezzocannone 8, I-80134 Naples, Italy e-mail: angelini@dgbm-unina.it Tel.: +39-81-2528911, Fax: +39-81-2528902 C. Falugi Istituto di Anatomia Comparata, University of Genoa, via Benedetto XV, I-16132 Genoa, Italy