Diplodus vulgaris

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Diplodus vulgaris

Ultrastructure features of spermiogenesis and spermatozoaThe mature spermatozoon is a simple elongated cellcomposed of a head, a short mid piece and a relativelylong tail or flagellum (Figure 7A). The head consistsmostly of an oval nucleus, that has very dense,homogenous and osmophilic chromatin material. Thesperm has no acrosome. The residual cytoplasmsurrounding the nucleus has a granular appearance.The midpiece encircles the flagellum and iscompletely separated from it by a cytoplasmic canal,that is an invagination of the plasmalemma, which runslongitudinally from the caudal to the cranial end of themidpiece and in which the flagella are located andemerged from the distal centriole. The centrosomedeeply engulfed by the nucleus in the nuclear fossa(Figure 7B). The cytoplasm extends toward a very longand thin flagellum which is a character to the marinespecies and is surrounded by the flagellar plasmamembrane. The insertion of the flagellum into the headis symmetric as indicated by the orientation of thecentrioles and the nucleus. One large ring ofmitochondria appears in one side lie within shallowdepression of the nuclear caudal surface (mitochondriasleeve) (Figures 7 - A & B).4. DiscussionAccording to the present study, Spermatogonia andSpermatocytes of D. vulgaris have limited finestructural variations with other teleosts species;however spermatids and spermatozoa have somepeculiar structures different from some other fishspecies.Spermatogonia occur singly or in small groups inall parts of the testis and each being almost completelysurrounded by sertoli cells. These cells perform severalfunctions for providing support and nutrition to thespermatogenic cells and in addition they phagocytizeresidual spermatozoa (Billard, 1970). They areconnected together by intering digitations, desmosomesand tight junctions.In D. vulgaris, mature spermatozoon has an ovalnucleus, which appears to be similar to the nucleidescribed in some characids (Burns et al., 1998 andMattei et al., 1995) and C. auratus (Shahin, 2007),while in some other teleosts species the nucleus isfound to be spherical in shape (Gwo et al., 1993 andGwo, 1995).As mentioned in the present study rotation of thenucleus is 90°, the diplosome inters the nuclear fossaand the flagellum is medial in position. Similar findingshave been recorded in Acanthopagrus schlegeli (Gwoet al., 1993) and Alestes dentex (Shahin, 2006).On the contrary, rotation of the nucleus are notcomplete as in Cyprinus carpio and Oreochromusniloticus (Lou & Takahashi, 1989) or entirely does notoccur as in Liza aurata (Brusle, 1981) and Diapoma sp.(Burns et al., 1998). In these cases, the diplosomeremains outside the nuclear fossa and the flagelluminserts laterally to the head.Grasssioto et al., 2001 indicated that, in thecommon teleost the nuclear fossa peneterates almost tothe tip of the nucleus. The centriolar complex and theinitial segment of the axoneme enter this fossa.This is in accordance with the present observationsin D. vulgaris; the nuclear fossa contains the centriolarcomplex and proximal portion of the flagellum. Thistype is common in the spermatozoa of many species asO. niloticus (Lou & Takahashi, 1989), Plecoglossusaltivelis (Gwo et al., 1994), Acanthopagrus latus (Gwo,1995), Chanos chanos (Gwo et al., 1995), PagellusErythrinus (Assem, 2003) and C. auratus (Shahin,2007).Nevertheless, the nuclear fossa is moderatelydeveloped in the curimatidae species (Grassiotto et al.,2003) and in the subfamilies Aphyocharacinae (Burnset al., 1998) while it is poorly developed inEpinephelus malabaricus and Plectropomus leopardus(Gwo et al., 1994). On the contrary, it is completelyabsent in most oviparous and some viviparous speciesas eels (Todd, 1976).Moreover, it has been described that the position ofcentriolar complex is related to the shape of nuclearfossa, when the nuclear fossa is deep, the centriolarcomplex is located inside it. If the nuclear fossa ismoderately deep, it may contain the entire centriolarcomplex or part of it, or only one of the centrioles,while the other one lies outside, but if it is completelyabsent, the centriolar complex usually lies close to thenucleus (Grassiotto et al., 2003).The present study shows that, D. vulgaris has twofibrous bodies which occupy the upper part of thenuclear fossa and connect the proximal centriole withthe nucleus and the basal foot, and alar sheets thatattach the basal body to the nucleus and plasmamembrane, respectively. They consist of osmophilicdisks alternating with lighter material and lieperpendicularly above the proximal centriole in theupper part of nuclear fossa. These two dense bodiesgive rise to two short electron dense fibers, whichconnect them together with the proximal centriole andanchor the latter to the nucleus. Similar findings havebeen described in the salmon O. m. formosanus (Gwoet al., 1996) and in the gadiform M. merluccius(Medina et al., 2003).Additionally, it has been pointed out that theposition of the nuclear fossa and accordingly theattachment of the flagellum to the nucleus depend uponthe rotation of the nucleus (Grassiotto et al., 2003). So,when the nuclear rotation is incomplete, the nuclearfossa is eccentric and so is the flagellum, which isperpendicular to the nucleus (Grassiotto et al., 2003;Jamieson, 1991and Burns et al., 1998). If the rotation iscomplete (90°) as in D. vulgaris, the nuclear fossa andthe flagellum are medial and perpendicular to thenucleus. But when the nucleus does not rotate, thenuclear fossa is lateral in position or may be also absentISSN: 1687-4285 Egyptian Journal of Aquatic Research, 2010, 36( ),

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