Th e order Siluriform es is greatly diversified, en com pass-in g m ore th an 35 fam ilies, ca 446 gen us an d 2867 species (NELSON 2006). Th e species of th is order occurs in th e tropical region , especially in South Am erica, Africa an d South east Asia (DE PINNA 1 9 9 8 ). Se v e r a l sp e cie s o f e co n o m ic in t e r e st su ch a s Pseudoplatystom acoruscans (Spix & Agassiz, 1829) an d P.fasciatum (Lin n aeus, 1766) belon g to th is order. Recen tly, th e m orph ol-ogy of th eir reproductive system h as been studied, in several works th at provided basic in form ation to th e un derstan din g of th e differen t reproductive strategies, ch aracteristics for ph ylo-gen etic an alysis, an d in form ation to be applied to aquiculture (BRITO & BAZZOLI 2003, ROMAGOSAetal. 2003, BATLOUNIetal. 2006). Th e fam ily Pseudopim elodidae is on ly foun d in South Am erica an d is still recogn ized as on e of th e less studied fam ilies of fresh -water Neotropical catfish . Lophiosilurusalexandri Stein dach n er, 1877 is a seden tary fish , n ative of th e São Fran cisco river basin ,
com m on ly kn own as “pacam ã”. It preferen tially in h abits len tic en viron m en ts, reproduces in captivity, h as adh esive eggs, th e m ales d isp lay p aren tal care an d h as econ om ic p oten tial for aquiculture (SATOetal. 2003, SHIBATTA 2003). Th e species was in -troduced in th e Doce river basin an d at th e presen t date th e effects of th is im pact un der th e n ative species h ad still n ot been studied (VIEIRA & POMPEU 2001).
Som e of th e fam ilies of th is order h ave frin ged testis with cells from th e sperm atic lin eage all alon g th eir exten sion ; oth -ers h ave sem in al vesicles or accessory stru ctu res at th e cau dal region th at do n ot display sperm atogen ic activity an d can store sperm atozoa (LEGENDREetal. 1996). Th e silu rifom Iheringichthys labrosus (Lü tken , 1874) h as frin ged testis with a cran ial m atogen ic region , a m iddle portion both secretory an d sper-m atogen ic an d a cau dal region exclu sively secretory (SANTOSet al. 2001). Th e testis of Loricarialentiginosa Isbrü cker, 1979 are
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M arcelo D. M . Barros; Rodrigo J. Guimarães-Cruz; Vanderlei C. Veloso-Júnior & José E. dos Santos
Programa de Pós-graduação em Zoologia de Vertebrados, Pontifícia Universidade Católica de M inas Gerais. Avenida Dom José Gaspar 500, Coração Eucarístico, 30535-610 Belo Horizonte, M inas Gerais, Brasil. E-mail: [email protected]
ABSTRACT. The gonad morphology and gametogenesis of Lophiosilurus alexandri Steindachner, 1877 from Santo Antônio river (Minas Gerais, Brazil) were studied through anatomical and histological techniques. Examination of the testis revealed that they were paired, fringed organs with two distinct regions: cranial spermatogenic and caudal spermatogenic and secretory. The cranial region represents ca. 60% of the mature/maturing testis, containing 41 to 73 fringes, while the caudal portion represents ca. 40% and contains 44 to 68 fringes. At the cranial portion the length of the fringes was 3.70 ± 1.70 mm and in the caudal portion was 0.20 ± 0.10 mm. The spermatogenesis was cystic, synchronic, and occurred throughout the whole extension of the seminiferous tubules. The ovaries were saculiforms, paired organs, which present ovigerous lamellae containing cells of the oogenic lineage. The oocytes were classified into four developmental stages according to their cytological characteristics and the characteristics of the cell layers that surround them.
KEY WORDS. Gonads; morphology; oogenesis; Pseudopimelodidae; spermatogenesis.
RESUMO. AAAAAparparparparparelhoelhoelhoelho rrrrreprelho eprodutoreprepreprodutorodutorodutor eodutor eeee gametogênesegametogênesegametogênesegametogênesegametogênese dede dedede LophiosilurusLophiosilurusLophiosilurusLophiosilurusLophiosilurus alexandrialexandrialexandrialexandrialexandri SteindachnerSteindachner (PiscesSteindachnerSteindachnerSteindachner (Pisces(Pisces(Pisces(Pisces, TTTTeleosteiTeleosteieleosteieleostei,eleostei Silur
Silur Silur Silur
Silurifififififororororormes).mes).mes).mes).mes). A morfologia das gônadas e a gametogênese de Lophiosilurusalexandri Steindachner, 1877 do rio Santo Antônio, bacia do rio Doce, Minas Gerais, foram estudadas através de técnicas anatômicas e histológicas. Os testículos são órgãos pares, franjados e apresentam regiões cranial espermatogênica e caudal espermatogênica e secretora. A região cranial corresponde aproximadamente a 60% do comprimento do testículo em maturação/ maduro e contém de 41 a 73 franjas e a região caudal representa 40% e possui de 44 a 68 franjas. Na região cranial o comprimento das franjas é 3,70 ± 1,70 mm e na região caudal 0,20 ± 0,10 mm. A espermatogênese ocorre de forma sincrônica, em cistos, e em toda a extensão da parede dos túbulos seminíferos. Os ovários são órgãos pares, saculiformes e, histologicamente, apresentam lamelas ovígeras que contém as células da linhagem ovogênica. Os ovócitos foram classificados em quatro fases de desenvolvimento, com base em suas características histológicas e das camadas que os circundam.
n ot frin ged an d, at th eir cau dal region , presen t a diffu se secre-tory tissu e th at does n ot form a con spicu ou s glan d (GUIMARÃES -CRUZet al. 2005).
In fish es, as in oth er an am n iotes, th e un it of sperm atoge-n esis is a sperm atocyst, usually referred to as a cyst. Th e devel-opm en t of th e cyst begin s wh en a prim ary sperm atogon iu m becom es associated with a som atic cell wh ich com pletely en ve-lopes th e germ cell with th in cytoplasm ic processes. Th e pri-m ary sperpri-m atogon iu pri-m th en divides pri-m itotically to produ ce a n um ber of secon dary sperm atogon ia. Sperm atogon ia th en en -ter m eiosis to form sperm atocytes. Durin g sperm atogen esis all germ cells with in a cyst are approxim ately at th e sam e ph ase of developm en t. Th e size of th e cyst in creases due to th e m atura-tion of germ cells, developm en t of a lum en , as well as by growth an d differen tiation of th e som atic cells. Followin g m eiosis, sper-m iogen esis en sues with th e forsper-m ation of spersper-m atids. Fin ally, a clon e of isogen etic sperm atozoa are form ed (PUDNEY 2003).
Th e fem ale reproductive system of som e Siluriform es spe-cies th at h ave been studied is ch aracterized by h avin g paired, elon gated ovaries wh ich com m un icate th rough th e oviduct with th e urogen ital papillae an d are located dorsally in th e coelom ic cavity (ROMAGOSAet al. 2003, GUIMARÃES-CRUZet al. 2005). Th e ovaries are surroun ded by a capsule m ade of den se con jun ctive tissue th at con stitutes th e tun ica albugin ea an d em its projec-tion s to th e in terior of th e organ wh ere it form s th e ovigerous lam ellae. Th ese lam ellae give support to th e germ cells durin g th e differen t stages of th eir developm en t (BAZZOLI 2003). Th ere are two m ain stages durin g th e developm en t of th e oocytes in teleosts: th e gon adotroph in s-in depen den t prim ary growth , an d th e secon dary growth wh ich is depen den t on gon adotroph in s (SELMAN & WALLACE 1989, TYLER & SUMPTER 1996). Th e perin ucleolar stage takes place durin g th e prim ary growth wh ile th e vitello-gen esis occurs durin g th e secon dary growth (PATIÑO & SULLIVAN 2002). Durin g follicle form ation m orph ologic ch an ges take place in th e n ucleus, ooplasm , zon a radiata an d follicular cells (GRIER 2000). In several fish species, after th e spawn in g an d du rin g em bryon ic developm en t, specialized structures presen t at th e oocytes surface can m ediate in teraction s between th e eggs an d th e differen t substrates wh ere th ey are deposited (RIZZO et al. 2002). In som e Siluriform es, th e jelly coat located extern al to th e zon a radiata can be related to th e adh esiven ess of th e eggs to th e substrate (RIZZO & GODINHO 2003).
In th is study, th e m orph ology of th e gon ads an d th e gam e-togen esis of L.alexandri (Fig. 1) were an alyzed usin g an atom ic, m orph om etric an d h istological tech n iques, in order to provide basic in form ation for th e com preh en sion of th e species reproduction an d th e ph ylogen etic relation sh ips between Siluriform es species.
MATERIAL AND METHODS
Specimens
Adults specim en s of L.alexandri, com prisin g 27 m ales an d 16 fem ales, were captured trim on th ly at th e San to An tôn io River (19º09’11”S, 42º41’23”W), state of Min as Gerais, south east
Bra-zil (Fig. 2). Th e fish es were collected between July/2004 an d Jun e/ 2005 usin g gill n ets with m esh sizes 8 to 16 cm (stretch ed m ea-surem en t).
Anatomy
Total len gth (cm ) an d weigh t (g) were recorded for each specim en . Gon ads (ovaries an d testis) were dissected, m easu red lon gitudin ally (cm ) an d weigh ted (g). Results are sh own in table I. Th e testis were divided an atom ically in cran ial an d cau dal region s. Twen ty m aturin g/m ature testis were fixed in 10% form -aldeh yde to be u sed in th e q u an tification of th e n u m ber of frin ges, an d th e len gth of th e frin ges in both region s (cran ial an d cau dal) was registered u sin g a pach ym eter. Th e m ean an d stan dard deviation were calcu lated.
Light Microscopy
Wh ole gon ads an d fragm en ts of th e cran ial an d caudal portion s of testis an d ovaries were fixed in Bouin ’s solution for 8 to 12 h ours, em bedded in paraffin , cut in 5 to 7 m m serial sec-tion s an d stain ed with h em atoxilin -eosin (HE) an d Gom ori trich rom e.
Classical h istoch em ical tech n iq u es (PEARSE 1985) were u sed for th e d etection of carboh yd rates an d p rotein s in th e Fig ures 1 -2 . (1 ) M ale sp ecim en of Lop h iosilu r u s a lexa n d r i
Steindachner, 1877, dorsal view. Scale bar = 1.0 cm. (2) Doce river basin, highlighting the sample area at Santo Antônio River.
1
caudal region of th e m aturin g/m ature testis: Periodic Acid-Sch iff (PAS), Alcian Blu e (AB) pH 2.5 an d AB pH 0.5 an d Nin h ydrin -Sch iff (NS). Ovaries slides con tain in g vitellogen ic oocytes were also treated with PAS.
Th e diam eters of 100 n u clei from cells in each stage of th e sperm atogen ic an d oogen ic lin eages were m easu red u sin g a m icrom etric ru le attach ed to th e ocu lar of a zeiss ligh t m i-croscopy. Th e th ickn ess of th e zon a radiata in previtellogen ic an d vitellogen ic oocytes an d th e h eigh t of th e follicu lar cells in ad van ced p erin u cleo lar, p revit ello gen ic an d vit ello gen ic oocytes were also m easu red. Th e m easu red cells were selected from 15 h istological preparation s of ovaries an d 15 of testis, takin g in accou n t th e in tegrity of th e cells (n o eviden ce of retraction ). For all th e m easu red stru ctu res th e m ean an d stan -dard deviation were calcu lated.
RESULTS
Testis Morphology
Th e testis are paired organ s, frin ged in all th eir exten -sion . Establish an atom ical relation s with th e swim bladder an d kidn eys dorsally an d with th e in testin e ven trally. No m ales in restin g stage were cap tu red . Th e m atu rin g/ m atu re testis are wh itish , bu lky, with tu rgid an d well developed frin ges (Fig. 3). Left an d righ t testis join togeth er cau dally, an d presen t a com -pact m edial region an d a lateral portion con stitu ted by frin ges. Th e frin ges com m u n icate with th e com pact region in dividu -ally or associated in p airs or trip lets.
Th e cran ial region represen ts ca. 60% of th e testes len gth , con tain in g 41 to 73 frin ges, wh ile th e cau dal p ortion rep re-sen ts ca. 40% an d con tain s 44 to 68 frin ges (Fig. 3). At th e cran ial portion th e len gth of th e frin ges is 3.70 ± 1.70 m m an d in th e cau dal portion is 0.20 ± 0.10 m m .
Th e frin ges at th e cran ial region are exclu sively sperm ato-gen ic (Fig. 4) wh ile in th e cau dal region sp erm atoato-gen ic an d secretory frin ges can be fou n d (Fig. 5). Th e secretion was observed associated with sp erm atozoa, at th e lu m en of th e tu -bu les an d in th e com m on sperm atic du ct (Fig. 6). Th is secre-tion reacts positively to th e PAS an d NS tech n iq u es, in dicatin g th e presen ce of n eu tral glycoprotein s.
Th e testis are extern ally coated by a capsule of con jun c-tive tissue (th e albugin ea). Th e albugin ea projects to th e in terior
of th e organ form in g com partm en ts th at con tain tubules wh ich com m un icate with th e sperm atic ducts. Th e sperm atic ducts of th e righ t an d left testis are join ed at th eir caudal portion , form -in g th e com m on sperm atic duct th at exten ds to th e urogen ital papillae, situated caudally to th e an al orifice (Figs 3 an d 7). Th e testicular paren ch ym a is located between th e albugin ea an d th e sperm atic duct an d is form ed by sem in iferous tubules an d in ter-stitial tissue. Th e sem in iferous tubules presen t a wide lum en an d an epith elium con stituted by cysts, with germ cells in differen t developm en tal stages (Fig. 11). Th e lim its of th e cysts are de-fin ed by cytoplasm ic exten sion s of th e Sertoli cells (Fig. 12). Th e cysts break apart at th e en d of th e sperm atogen esis releasin g th e sperm atozoa in th e tubules lum en , wh ich an astom osized. Th e sperm atozoa reach th e sperm atic ducts an d th en th e com m on sperm atic duct, wh ere th ey are stored un til sperm iation . Th e in terstitial tissue is con stituted by cells an d fibres of con jun ctive tissue, m yoid cells, blood vessels an d Leydig’s cells (Fig. 13). Th e Leydig’s cells wh ich were observed both isolated or in groups, are roun ded, with acidoph ilic cytoplasm an d h ave a n ucleus with diffuse ch rom atin an d con spicuous n ucleolus. Th e wall of th e urogen ital papillae is form ed by sim ple prism atic epith elium an d a con jun ctive-m uscular basal lam in a (Fig. 7).
Spermatogenic lineage cells (Fig. 11)
Prim ary sp erm atogon ia: th e largest cell of th e lin eage, occu rrin g on ly on e per cyst. It h as abu n dan t cytoplasm an d a sph erical cen tral n u cleu s (Ø = 5.78 ± 0.64 µ m ) with an eviden t n u cleolu s.
Secon dary sperm atogon ia: th ey form cysts with two to four cells. Th ey presen t little cytoplasm ic m aterial an d a sph eri-cal cen tral n ucleus (Ø = 4.37 ± 0.48 µ m ) with on e or two n ucleo-lus.
Prim ary sperm atocyte: origin ated from th e last gen eration of secon dary sperm atogon ia after successive m itotic division s. Th ey presen t little cytoplasm ic con ten t an d a sph erical cen tral n ucleus (Ø = 3.24 ± 0.74 µ m ) with gran ulated ch rom atin .
Secon dary sperm atocyte: origin ated from th e first m ei-otic division of prim ary sperm atocytes. It h as little cytoplas-m ic con ten t an d a cen tral sph erical n u cleu s (Ø = 2.30 ± 0.46 µ m ) with fin e ch rom atin .
Sperm atid: it h as little cytoplasm ic con ten t an d a den se sph erical n u cleu s (Ø = 1.88 ± 0.33 µ m ).
Sp erm atozoa: is th e sm allest of th e sp erm atogen ic lin eage. It presen ts a sph erical h ead with little cytoplasm ic con -ten t an d a con den sed n u cleu s (Ø = 1.17 ± 0.38 µ m ).
Ovaries morphology
Th e ovaries are paired, saculiform s organ s (Fig. 8), an a-tom ically related to th e swim bladder an d kidn eys dorsally an d with th e in testin e ven trally. Restin g ovaries are wh itish , tran slu-cen t, presen t few in con spicuous blood vessels, an d con tain oo-gon ia an d perin ucleolar oocytes. Th e m aturin g/m ature ovaries are bulky, yellowish , with oocytes th at are visible to th e n aked eye, h ave eviden t vascularization (Fig. 8) an d a predom in an ce
Table I. M inimum and maximum values for total lenght (TL), body weight (BW), longitudinal length of the gonads (LLG) and gonad weight (GW) in L. alexandri.
M ale Female
M inimum M aximum M inimum M aximum
TL (cm) 26.50 60.00 33.80 65.00
BW (g) 293.00 2613.00 605.00 3500.00
LLG (cm) 5.10 9.70 3.70 9.00
Figures 3-10. M ale and female mature reproductive systems: embedded in paraffin and stained with hematoxilin-eosine (Figs 4 to 7 and 10) and Gomori’s trichrome (Fig. 9). (3) Fringed testis showing the cranial (Cr) and the caudal (Cd) regions, the anus (A), and the urogenital papillae (P); (4) Cranial region during spermatogenic activity, showing the tunica albuginea (TA), the seminiferous tubules (ST) and cysts of spermatogenic lineage cells in different developmental stages; (5) Caudal region with secretory (*) and spermatogenic activity; (6) Common spermatic duct showing spermatozoa (*) and secretion in the lumen; (7) Transversal section of the urogenital papillae (P) and the anus (A); (8) M aturing ovaries, showing the ovarian duct (OD), the anus (A) and the urogenital papillae (P); (9) Section of the maturing ovary showing the initial perinucleolar oocyte (O1), the advanced perinucleolar oocyte (O2) and the vitellogenic oocyte (O4); (10) M aturing ovarian duct showing the prismatic epithelium (arrow). Scale bar: Figures 3 and 8 = 1cm; Figures 4 to 7, 9 and 10 = 100 µm.
of p revitellogen ic an d vitellogen ic oocytes (Fig. 9). Th ey are coated with a th ick tun ica albugin ea form ed by con jun ctive tis-sue, m uscular fibres an d blood vessels. Th e albugin ea sen ds septa to th e lu m en form in g th e ovigerou s lam ellae wh ere n ests of oogon ia an d oocytes in differen t developm en tal stages can be foun d. Left an d righ t ovaries join at th e caudal portion form in g th e com m on ovarian duct th at com m un icates with th e urogen i-tal papillae (Fig. 8). Th e wall of th e com m on ovarian duct in m aturin g/m ature ovaries is form ed by sim ple prism atic epith e-lium restin g over a con jun ctive tissue layer (Fig. 10).
Oogenic lineage cells (Figs 14-18)
Oogon ia: th e sm allest cell (Ø = 9.08 ± 0.91 µ m ) of th e lin eage. Th ey are rou n ded cells fou n d grou ped in n ests at th e ovigerou s lam ellae. Th ey h ave little cytoplasm ic con ten t, with a n u cleu s with diffu se ch rom atin an d a u n iq u e an d prom in en t n u cleolu s.
Advan ced p erin u cleolar oocyte: th e cell (Ø = 274.40 ± 12.94 µ m ) h as a basoph ilic fin ely gran u lated ooplasm an d a n u cleu s with diffu se ch rom atin an d n u cleoli attach ed to th e n u clear m em bran e. Th e yolk n u cleu s is prom in en t, begin n in g n ext to th e cellu lar n u cleu s an d th en m igratin g to th e periph -ery wh ere it disperses. Th e zon a radiata is th in an d acidoph ilic. Th e m icrop yle cell closes th e m icrop ilar ap p aratu s, wh ich is form ed by th e vestibu le an d a sh ort m icropylar du ct. Th e folli-cu lar cells are sq u am ou s with 11.15 ± 1.25 µ m h eigh t.
Previtellogen ic oocyte: th e cell (Ø = 820.18 ± 58.23 µ m ) basoph ily of th e cytoplasm dim in ish es gradu ally an d cortical alveoli are form ed in th e ooplasm a periph ery. Th e n u cleu s is cen tral, with d iffu se h eteroch rom atin an d th e n u cleolu s at-tach ed to th e n u clear en velope. Th e zon a radiata is acidoph ilic an d sh ows 1.59 ± 0.49 µ m th ickn ess. Th e follicu lar cells are cu bic an d 18.44 ± 1.79 µ m h igh .
Vitellogen ic oocyte: it is th e largest cell (Ø = 1409.08 ± 72.53 µ m ) of th e lin eage, ch aracterized by th e presen ce of aci-doph ilic yolk globu les in th e ooplasm . Th e yolk globu les at th e m icropyle region are sm aller th an oth er cytoplasm ic yolk glob-u les foglob-u n d in th e sam e cell. Th e zon a radiata is 1.35 ± 0.48 µ m th ick. Th e follicu lar cells are p rism atic, PAS p ositive, 30.16 ± 2.71 µ m h igh an d redu ce th eir h eigh t gradu ally as th ey be-com e closer to th e m icropyle.
DISCUSSION
Th e an atom ical relation sh ips of testis an d ovaries of L. alexandri are sim ilar to th e on es fou n d in oth er fresh water Silu riform es th at h ave extern al fertilization su ch as P.coruscans (BRITO & BAZZOLI 2003) an d P. fasciatum (ROMAGOSAet al. 2003, BATLOUNIetal. 2006).
Th e an atom ical organ ization of th e testis in Siluriform es h as been sh own to be variable am on g th e fam ilies but th e m a-jority of th em presen t frin ged testis: Ictaluridae (SNEED & CLEMENS 1963); Claridae (SIRCAR 1970); Au ch en ipteridae (MEISNER et al. 2000); Doradidae (GUIMARÃES-CRUZ & SANTOS 2003); Pim elodidae (SANTOSetal. 2001, BRITO & BAZZOLI 2003, GUIMARÃES-CRUZ & SANTOS 2004, LOPESet al. 2004, BATLOUNIet al. 2006) an d Pseudopim e-lodidae (th is stu dy). A stu dy u sin g th ree differen t sp ecies of Siluriform es sh owed th at th e testes len gth , th e total n um ber of frin ges an d th eir len gth presen ted differen t values in th e caudal an d cran ial portion s (GUIMARÃES-CRUZ & SANTOS 2004). Th e values obtain ed for L.alexandri were also differen t. Th e variation of th e len gth between cran ial an d caudal frin ges probably could be explain ed by th eir differen t fun ction s. In th e cran ial region th e frin ges in crease in len gth an d diam eter by m ultiplication of spm atogen ic lin eage cells in th e sespm in iferous tubule walls. Oth er-wise, th e sm aller developm en t of th e caudal frin ges can be ex-plain ed by th e on ly presen ce of a secretor epith eliu m in th e tubules wall.
So m e fam ilies o f t h e o rd er Silu rifo rm es t h at p resen t frin ged testis sh ow secretory activity at th eir cau dal portion s, som etim es h avin g a sem in al vesicle (LOIRetal. 1989). Th e cau
-dal frin ges of th e m atu rin g testis of L.alexandri presen ted tu -bu les in tern ally coated by prism atic, secretory cells, with th eir lu m en filled by secretion an d sperm atozoa. Th e ch em ical n a-tu re of th e secretion presen t in th e lu m en of th e a-tu bu les in th e cau dal frin ges varies am on g Silu riform es species. In Pim elodus m aculatus La Cepède, 1803 n eu tral glycoprotein s an d carboxy-lated acid glycocon ju gates su ch as sialom u cin s an d su lph ated an d acid glyco co n ju gat es were d et ect ed (GUIM ARÃES-CRUZ & SANTOS 2004); in I.labrosus (SANTOSet al. 2001) an d L.alexandri (th is work), on ly n eu tral glycop rotein s were fou n d. Th is secre-tion m ay h ave sim ilar fu n csecre-tion s as th ose exh ibited by su b-stan ces produ ced in th e sem in al vesicles of oth er teleost fish es, con tain in g glycoprotein s, steroid h orm on es an d ph erom on es th at can in crease th e volu m e of th e sem in al flu id an d can be in volved in fem ales attraction an d in th e fertilization process (LAHNSTEINERetal. 1992, MAZZOLDIetal. 2005).
In L.alexandri, th e sperm atogen ic cells are distribu ted in cysts, all alon g th e exten sion of th e sem in iferous tubules, wh ich an astom osis to con duct th e sperm atozoa to th e sperm atic ducts, as is ch aracteristic of an an astom osin g tu bu lar testes organ iza-tion (PARENTI & GRIER 2004). Th e sperm atic lin eage cells, after several division s of th e prim ary sperm atogon ia, acquire th e typi-cal m orp h ology of each d evelop m en tal stage (BILLARD 1970, PUDNEY 1993).
In teleosts, in clu d in g L. alexandri, th e cytop lasm ic ex-ten sion s of th e Sertoli cells con tribu te to th e form ation an d su sten tation of th e cysts, an appropriate place for th e differen -tiation an d proliferation in clon e germ cells (PUDNEY 1996). In L.alexandri, th e breakin g of th e cystic walls allows th e releas-in g of sp erm atozoa, as is also th e case releas-in sp ecies su ch as I. la brosu s (SAN TO S et al. 2 0 0 1 ) a n d C on ory n ch u s con irost ris (Valen cien n es, 1840) (LOPESetal. 2004).
Th e m orph ology an d distribu tion of Leydig’s cells vary with th e differen t vertebrates species (PUDNEY 1996). Th ey p ro-du ce steroids th at are im p ortan t for sp erm atogen esis regu la-tion , th e developm en t of secon dary sexu al ch aracters an d re-productive beh aviour (WELTZIENetal. 2004). In L.alexandri, th ese cells are rou n ded an d were observed isolated or in grou ps in -side th e testes strom a.
Th e m orph ology of th e ovaries of L.alexandri is sim ilar to th e m orph ology of th e ovaries of oth er Siluriform es as P.coruscans (BRITO & BAZZOLI 2003), P. fasciatum (ROMAGOSAet al. 2003), I. labrosus (SANTOSetal. 2004) an d L.lentiginosa (GUIMARÃES-CRUZet al. 2005). Followin g HOAR (1969) classification th e ovaries of L. alexandri are cystovarian , sin ce th ey presen t a com plete ovarian capsule an d an ovarian duct.
in to th e perivitellin ic space in order to block p olysperm y after fertilization (MICALEetal. 1999). Du rin g secon dary growth , th e oocyte in creases its diam eter du e to th e accu m u lation of yolk (JALABERT 2005). It was observed th at th e vitellogen ic oocytes in L.alexandri in creased th eir diam eter in ca. 1.304% wh en com -pared to th e in itial perin u cleolar oocytes size. Th e vitellogen ic oocytes of species su ch as Daniorerio (Ham ilton , 1822) (BECKER & HART 1999) an d Synbranchusm arm oratus Block, 1795 (RAVAGLIA & MAGGESE 2002) h ave sm aller yolk globu les at th e periph ery an d bigger globu les at th e cen tral region . In L.alexandri it was observed th at sm aller yolk globu les are located on ly in th e m icropyle region , possibly to facilitate th e displacem en t of th e p ron u cleu s to be fertilized.
Th e th ickn ess an d stru ctu re of th e zon a radiata depen d on th e species an d reflect adaptation s to differen t ecological con dition s (FAUSTOet al. 2004). Silu riform es belon gin g to th e Loricariichthys an d Loricaria gen u s presen t a th ick zon a radiata (9.1 ± 0.57 µ m an d 9.95 ± 0.25 µ m , respectively), wh ich m igh t be an adaptation to protect th e developin g eggs sin ce th e m ales carry th em attach ed to th e ven tral su rface of th eir bodies in a way th at m akes th e eggs su sceptible to ph ysical dam age du e to con tact with th e su bm erse su bstrates (SUZUKIet al. 2000). On th e oth er h an d, L.alexandri presen ted a th in zon a radiata (1.35 ± 0. 48 µ m ), wh ich m igh t be explain ed by th e fact of th e eggs were n ot bein g exposed to ph ysical dam age, sin ce th ey are de-posited in n ests an d in cu bated by th e m ales. In th is stu dy th e zon a rad iata of p revitellogen ic an d vitellogen ic oocytes was observed as well as a m icropyle apparatu s with a wide vesti-bu le an d a sh ort m icrop yle d u ct, corresp on d in g to a typ e 1 m icropyle in th e classification by RICARDOetal. (1996).
Th e follicular cells origin ate from th e germ epith elium of th e ovaries, wh en prefollicular cells em it processes th at surroun d th e oocytes durin g m eiosis (GRIER 2000). QUAGIO-GRASSIOTTO & GUIMARÃES (2003) related th at th e follicular cells of th e teleost Serrasalm usspilopleura Kn er, 1858 are squam ous durin g th e pri-m ary growth an d becopri-m e cuboidal durin g th e secon dary growth ph ase, acquirin g ch aracteristics typical of protein s or glycopro-tein s producin g cells. Th e an alysis of follicular cells in L.alexandri dem on strated th at m ost of th em are squam ous durin g th e pri-m ary growth an d becopri-m e h igh -prispri-m atic at th e en d of th e sec-on dary growth , th e exceptisec-on bein g th e cells n ear th e m icro-pyle region th at were foun d to be squam ous/cubic. Th e siluriform Cathoropsspixii (Spix & Agassiz, 1829) presen ts h igh follicular cells capable to syn th esize th e adh esive m aterial th at covers th e eggs after th e spawn an d th e adh esiven ess of th e eggs facilitates paren tal care (FÁVARO et al. 2005). In th e siluriform I.labrosus, th e follicular cells of vitellogen ic oocytes sh owed secretory ac-tivity producin g electron -ligh t gran ules sim ilar to m ucosom es, wh ich con tain acid glycocon jugates an d can be related to th e eggs a d h esiv en ess (SAN TO S et al. 2 0 0 6 ). Th e p resen ce o f m ucosubstan ces in th e follicular cells of th e vitellogen ic oocytes of L.alexandri was con firm ed durin g th is study. Th ese substan ces can be related with eggs adh esiven ess as it h as been observed in
th e siluriform Silurusglanis Lin n aeus, 1758 (ABRAHAMetal. 1993). In su m m ary, L.alexandri presen ts frin ged testis with th e cran ial region bein g sp erm atogen ic wh ile th e cau d al region p resen ts both sp erm atogen ic an d secretory activities. Testes organ ization is of th e an astom osin g tu bu lar type an d th e sper-m atogen esis is cystic. Th e ovaries are of th e cystovarian type, t h e o o cyt es a re a d h esive a n d t h e fo llicu la r cells secret e m u cosu bstan ces. All th ese ch aracteristics are im portan t crite-ria for ph ylogen etic an alyses am on g Silu riform es an d are u se-fu l for th e better com preh en sion of th eir reprodu ction , sin ce th is species h ave a good poten tial for aq u icu ltu re.
ACKNOWLEDGEMENTS
Th e au th ors are gratefu l to: FIP PUC Min as for fin an cial su p p o rt (p ro ject 2004/ 17–TLE); t h e lab o rat o r y t ech n ician s Ru ben s Miran da an d Rogério S. Matos for preparation s of th e h istological plates, an d to Ren ê E.S. Hojo for th e assistan ce du r-in g th e collects of th e fish es.
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