Morphological study of the oviductal gland in the smallnose fanskate Sympterygia bonapartii (Müller and Henle, 1841) (Chondrichthyes, Rajidae) Galíndez EJ.a*, Díaz-Andrade, MC.a, Avaca, MS.b and Estecondo, S.a aLaboratorio de Histología Animal, Departamento Biología, Bioquímica y Farmacia, Universidad Nacional de San Juan – UNS, San Juan 670, (8000), Bahía Blanca, Buenos Aires, Argentina bInstituto de Biología Marina y Pesquera Almirante Storni, Güemes 1030, (8520) San Antonio Oeste, Río Negro, Argentina *e-mail: [email protected] Received April 30, 2008 – Accepted February 26, 2009 – Distributed XXXXX XX, XXXX (With 18 figures) Abstract The oviductal gland is an exclusive structure of cartilaginous fishes that produces the egg jelly, forms the tertiary egg envelopes and stores sperm. The biological importance of this structure is related to the special features of the reproductive strategy of the group and to its phylogeny, considering that egg-laying is the ancestral condition in this fish (Dulvy and Reynolds, 1997). This gland of the smallnose fanskate shows four morphofunctional zones. The lin- ing epithelium along the gland is columnar with secretory and ciliated cells. Secretions are mucous and/or proteic according to the zone, and to their specific functions. This is the first report about the microanatomy of the female reproductive tract of S. bonapartii with evidence of sperm storage in the genus. Keywords: Chondrichthyes, Rajidae, oviductal gland, reproductive biology, Sympterygia bonapartii. Estudo morfológico da glândula oviductal no smallnose fanskate Sympterygia bonapartii (Müller and henle, 1841) (Chondrichthyes, Rajidae) Resumo A glândula oviductal é uma estrutura exclusiva das elasmobrânquias que produz a geléia do ovo, o envoltório terciário do ovo e armazena espermatozóides. Sua importância está relacionada com as características especiais da estratégia reprodutiva do grupo e com a filogenia destes peixes em que oviparidade é a condição ancestral (Dulvy and Reynolds, 1997). A glândula oviductal do smallnose fanskate mostra quatro zonas morfofuncionais. O revestimento em toda a glândula é epitélio colunar ciliado com células glandulares e ciliadas. As secreções são diferentes entre as zonas e relacionada com as suas funções específicas. A informação aqui exposta constitui o primeiro relato sobre a micro-ana- tomia do trato reprodutivo feminino de S. bonapartii com evidencias de armazenamento do esperma neste gênero. Palavras-chave: Chondrichthyes, Rajidae, glândula oviductal, biologia reproductiva, Sympterygia bonapartii. 1. Introduction Through their evolutive history, cartilaginous fishes worldwide (Stehmann, 2002). Since 1994, there has been have remained as major components of marine commu- an increase in exploitation exerted on chondrichthyes in nities with the ability to adapt to varying selective pres- Argentina, resulting in a decrease in stocks of the com- sures. Their success is due, in part, to biological features mercially most important species (Massa et al., 2003). such as slow growth, delayed sexual maturity, low egg Fisheries targeting teleosts and shrimps (Cedrola et al., production and long reproductive cycles (Hoenig and 2005) also incidentally catch Elasmobranchs. Bycatched Gruber, 1990; Hamlett, 2005), all of them adaptations to skates have increased significantly in recent years (Massa maximise fecundity (Lucifora and García, 2004). and Hozbor, 2003) with strong evidence of overexploita- Increased human exploitation, the biological fea- tion for some species (Chiaramonte, 1998; Chiaramonte tures of the group and the pollution of the sea, have and Pettovello, 2000; Massa et al., 2004). depleted several species, at least on a regional basis The genus Sympterygia is endemic to temper- (Miranda and Vooren, 2003) threatening elasmobranchs ate waters of South America and is represented in the Braz. J. Biol., XXXX, vol. XX, no. X, p. XXX-XXX X Galíndez EJ. et al. Argentinean Sea by two species: S. bonapartii (Müller (38° 45’-39° 45’ S and 61° 30’-62° 30’ W). In each cap- and Henle, 1841) and S. acuta Garman, 1877 (Menni, ture, sea depth was no more than 10 m. 1976). The smallnose fanskate is found from southern Animals were humanely sacrificed by blunt trauma, Brazil to Argentina (Menni and Stehmann, 2000) and it measured and immediately dissected. For light micro- is one of the major skates that has been caught along the scopy, tissue samples were fixed in Bouin’s fixative or Buenos Aires coast during recent years. This fact places 10% formaldehyde, both of them in seawater, dehydrat- the species under great fishing pressure (Massa et al., ed through a graded series of ethanol and embedded in 2003). Females are oviparous and use the Bahía Blanca paraffin wax. Sections of 5-7 micrometers were stained estuary as a breeding and nursery area during spring and with hematoxylin-eosin, Masson’s trichromic, periodic summer (Cousseau and Perrotta, 1998). Its biology is acid Schiff reaction (PAS) and alcian blue (pH 2.5 and poorly known and only the basic aspects of reproduc- 1.0) techniques. Sections were examined and photo- tive features, such as length at first maturity, sexual di- graphed under an Olympus BX 51 microscope with an morphism, size at hatching and some laying areas, are Olympus Camedia C-7070. For scanning electron micro- known (Mabragaña et al., 2002; Oddone and Velasco, scopy, tissue samples from three mature females were 2004; Jañez and Sueiro, 2007). used. Small pieces of the oviductal gland were fixed in In spite of the extensive diversity of reproductive 2.5% glutaraldehyde in 0.05 M sodium cacodylate buffer strategies that elasmobranches exhibit, in all known with 12% sucrose (Hyder et al., 1983), for 12 hours at cases, the fertilised egg passes through the oviduct and 4 °C and post fixed in 1% osmium tetroxide in the same is encapsulated by secretions produced by the oviduc- buffer for 90 minutes at 4 °C. Samples were washed in tal gland, a specialised region of the anterior oviduct the same buffer, dehydrated in graded acetona, dried by (Hamlett, 2005). This gland also forms the tertiary egg critical point, coated with Au-Pd by the ion-sputtering envelopes, transfers eggs to the uterus, and stores sperm method and examined in an Evo 40 XVP (Cambridge, (Pratt, 1993; Smith et al., 2004). The knowledge of the England) scanning electron microscope at 6 KeV. Part of structure and function of this organ is restricted to spe- these samples was also embedded in Spurr’s low density cies of the northern hemisphere and Australia (Hamlett resin and semithin sections were stained with 1% tolui- et al., 1998; Stevens, 2002; Smith et al., 2004) and only dine blue. one species of the genus Sympterygia has been studied (Galíndez and Estecondo, 2008). The gross morphology 3. Results of the oviductal gland varies between species but, in gen- eral, consists of two similar dorsoventral flattened halves The smallest mature female was 425 mm of total surrounded by connective tissue (Knight et al., 1996). length (TL) and the largest immature was 642 mm of The architecture and development of the gland are close- TL. ly related to the reproductive mode, the maturity stage, The female tract is composed of two ovaries, with the reproductive season and reproductive cycle stage. the left slightly larger than the right one, 2 oviducts, Notwithstanding, there can be recognised four differ- 2 oviductal glands (OG) and 2 uterus that end in 1 uro- ent zones characterised by its organization and different genital sinus (Figure 1). At the beginning of the mating staining affinities of the mucosa (Hamlett et al., 1998). season, the OG adopts a heart-shaped form and progres- The aim of this work was to study the microarchi- sively their half sizes increase more laterally than longi- tecture of the oviductal gland of an endemic species tudinally. In spite of this allometric growth, the length is of South America and to compare this data with other the prevailing dimension. In mature females, the mean Chondrichthyes, as well as to correlate the morphologi- width is 31.16 mm (SD = 0.309) and the mean length is cal features with the reproductive characteristics of this 33.70 mm (SD = 0.291). species. The knowledge of any aspect of reproductive The entire organ is composed of a mucosa, a very biology of elasmobranchs is of interest not only due to thin connective submucosa, a muscular layer formed by the fact that egg encapsulation is a conserved process longitudinal smooth muscle fibres and a serosa. throughout the evolutive divergence of these fishes, but The mucosa of the organ is folded in characteristic also for a better understanding of a very important eco- patterns (Figure 2) and according to this, it is possible to nomic resource for our fisheries, as well as a significant recognise four regions from cranial to caudal. biological contribution to aid to the managing of stocks. The anterior region (club zone) is continuous with the oviduct and is a short segment, which mucosa shows from 5 to 8 parallel lamelli (Figure 2 and 3). The lining 2. Materials and Methods epithelial cells are simple columnar and ciliated (Figure 3 For the histological study, we have used 12 sexually insert and 4). Cells located from the base to the apical mature females (at least stage III, according to Stehmann, region of the folds react positively to PAS (Figure 5). 2002) from a total of 17 specimens caught monthly from Short simple tubular glands open at the base of the folds. middle spring (September - October) to early summer They have two cellular types (Figure 6), one of them cili- (November - December). They were caught by line ated and the other plenty of PAS and AB pH 2.5 positive fishing in the inner area of the Bahía Blanca estuary small granules Figure 7. X Braz. J. Biol., XXXX, vol. XX, no. X, p. XXX-XXX The oviductal gland of Sympterygia bonapartii 4 m ovi µ ova 50 µm Figure 3.