Ovarian follicle growth in the catfish Iheringichthys labrosus (Siluriformes: Pimelodidae)

The morphofunctional organisation of the female reproductive system, the oocyte growth and the follicular envelope ultrastructure were studied by the first time in the catfish Iheringichthys labrosus from Upper Paraná River basin, Southeastern Brazil, in order to contribute to the knowledge of the reproductive behaviour strategies of this species. As in other Neotropical freshwater siluriforms, the ovaries are of the cystovarian type, the oocytes develop in an asynchronous pattern and mature oocytes are released in clusters in the ovarian lumen, being transported through the oviduct to the urogenital papilla. During the primary growth, nuclear material is transported to the ooplasm, forming the yolk nucleus, where proliferate membranous organelles. The onset of the zona radiata formation occurs during the late perionucleolar stage with the deposition of the outer layer. At the vitellogenic stage, this envelope reaches 6.35+/-0.84microm of thickness, being constituted by three distinct layers crossed by pore-canals containing oocyte and follicular cells processes. Cytochemical analyses evidence neutral glycoproteins in cortical alveoli, yolk globules and zona radiata. Follicular cells with squamous shape during the primary growth acquire synthetic activity at the secondary growth, reaching 37.82+/-4.72mum in height at the mature vitellogenic follicles. These cells accumulate sulphated polysaccharides in large electron-lucent vesicles during the vitellogenic stage which are possibly secreted to form a mucous coat at the egg surface. These evidences suggest that I. labrosus may have adhesive eggs as also detected in other Neotropical freshwater Siluriformes.     

Comparative oocyte morphology and early development in three species of trahiras from the São Francisco River basin, Brazil

Oocyte morphology, embryogenesis and early larval development were compared in Hoplerythrinus unitaeniatus , Hoplias lacerdae and Hoplias malabaricus (Characiformes: Erythrinidae) by macroscopical, histological, histochemical and ultrastructural analyses. The eggs of the three species were yellowish and adhesive, containing carboxyl and sulphate radicals in the glycoconjugates of the zona radiata. A complex surface arrangement was identified in oocytes of H. unitaeniatus and H. lacerdae , while H. malabaricus had a simple oocyte surface pattern. Lectin histochemistry revealed different carbohydrate terminal residues in cortical alveoli, outer zona radiata and follicular cells of the three species. At the animal pole, the oocyte surface topography surrounding the micropyle was species-specific. The micropylar cell was ConA-positive, suggesting the presence of carbohydrates with mannose/glucose terminal residues that could have a role during fertilization. The erythrinids exhibited a prolonged embryonic and larval development compared to other Characiformes, a reproductive strategy used for increasing offspring protection. Early development proceeded most rapidly in H. unitaeniatus , followed by H. malabaricus and then H. lacerdae , which could have more developed parental care behaviour. An adhesive organ composed of secretory prismatic cells protruding from the cephalic region of the three erythrinid larva allowed them to attach to one another during development. Reproductive behaviour and early developmental strategies were similar in the three species, but the oocyte surface morphology suggests a close relationship between H. unitaeniatus and H. lacerdae .     

Comparative ultrastructure of the zona radiata from eggs of six species of salmonids

Summary The zona radiata from unactivated and activated eggs from chinook salmon (Oncorhynchus tshawytscha), chum salmon (O. kisutch), pink salmon (O. gorbuscha), brown trout (Salmo trutta), rainbow trout (S. gairdneri) and lake trout (Salvelinus namaycush) were examined using scanning and transmission microscopy. The zona radiata in all species examined consisted of an outer adhesive coating, a thin densely staining zona radiata externa with pore canal plugs and a thick, fibrous zona radiata interna with a fibrous network on the inner surface. There was a two layer adhesive coating over the zona radiata externa in all species except pink salmon in which only one layer was observed. There were structural differences among species in the adhesive layer, zona radiata externa and plugs in the pore-canal openings.Scientific Journal Series, Paper No. 14,627, Minnesota Agricultural Experiment StationPartially funded by Minnesota Sea Grant NA-82-AA 12-000-39, Project RF-12, Minnesota Sea Grant Contribution 168     

Relationship between oocyte morphology and reproductive strategy in loricariid catfishes of the Paraná River, Brazil

Relationships between ovarian structure, oocyte structure/development, and parental care/life history strategies of six loricariid catfishes common in the upper Paraná River, Brazil were examined with analysis of catch data, relative gonad weight, histology, and microscopy. Three life history strategies were observed. Loricariichthys platymetopon , Loricariichthys sp. And Loricaria sp. produce several small clutches of large eggs over a protracted spawning period. Males of these species guard their eggs and larvae, which are transported as a mass on the ventral surface of the male's body. Hypostomus ternetzi and Megalancistrus aculeatus produce the largest mature eggs and the smallest clutches relative to adult mass. The spawning periods of these species are short, and males guard their broods in excavations. Rhinelepis aspera has high fecundity, high relative mass of mature gonads (both sexes), small mature eggs, and broadcast spawning with no parental care. This species migrates to spawn over firm substrates in channel areas during a contracted period. Mature oocytes of external bearers had the thickest zona radiata, followed by the egg scatterer, and cavity nesters. The thickness of the zona radiata probably is an adaptation to protect the developing egg from injury from abrasion. The zona granulosa appeared to be associated with production of secretions responsible for egg adhesion, and this layer was thickest in mature oocytes of the cavity nesting species, followed by the external bearers. All six species have wide distributions in the Paraná River, tributaries, floodplain lagoons, and the Itaipu Reservoir, but brood guarders tended to be most common in lentic habitats.     

Histological study on the oocyte filaments of the silverside Odonthestes bonariensis

Highly developed adhesive structures are characteristic of the eggs of Odonthestes bonariensis . At spawning each egg is connected to the other ones by four to six filaments. These are extroverted only in mature eggs, about 4–5 mm long and 10μm thick, starting from coneshaped bases at the egg's surface. Histologically, no filaments are detectable during the primary growth phase of the oocytes. At the lipidic vesicle stage, rounded eosinophilic filaments appear at the cell's surface. During the following stages they increase in volume and length, running along the whole oocyte, and lose their eosinophily. The filaments are beneath the follicular cells; according to preliminary TEM observations, they derive from the zona radiata. When the oocyte is mature, the theca externa disintegrates, freeing the filaments. These rather conspicuous and complex structures are markedly different from the adhesive egg fibrils observed in other teleosts.     

Comparative ultrastructural studies of the zona radiata of marine fish eggs in three genera in Perciformes

The eggs of Mugil cephalus were significantly larger than those of Epinephelus malabaricus , and E. coioides , while those of Sciaenops ocellatus were intermediate between E. coioides and M. cephalus . The distribution density of pores in the egg envelope of S. ocellatus was significantly different from that of E. malabaricus and E. coioides . The micropyle diameters were significantly different in the four species. The ultrastructure of the zona radiata surface, the distribution density of pores and the size of eggs were also useful characters for distinguishing among the four species, but the ultrastructural features of the micropyles were the most important of all for egg identification.     

Egg surface structure of three clingfish species, using scanning electron microscopy

The three eastern Atlantic gobiesocid species Lepadogaster lepadogaster, Apletodon dentatus and Diplecogaster bimaculata share an attachment apparatus consisting of numerous bifurcating filaments that originate at the animal egg pole and are embedded in a mucous layer. The thickness of the mucous layer and zona radiata, and the structure and size of the micropyle vary among the three species. Because of lack of information about egg structure in paracanthopterygians and percomorphs with adhesive demersal eggs, the phylogenetic significance of this character complex remains unclear.     

Changes in elemental composition of fertilized and unfertilized northern pike (Esox lucius) eggs incubated in buffer with and without dimethyl sulfoxide: An X-ray microanalysis study

Fertilized and unfertilized eggs from the northern pike (Esox lucius) were incubated 2 hr in buffer with 0 and 10% (v/v) dimethyl sulfoxide and then quickly frozen in the wells of aluminum blocks submerged in liquid nitrogen. Control eggs and ovarian fluid were similarly frozen immediately after collection. The frozen eggs were sectioned, freeze dried, mounted on stubs, and carbon coated. X-ray microanalysis was used to determine changes in element levels and dimethyl sulfoxide (Me₂SO) penetration in the zona radiata, cytoplasm, cortical alveoli, and egg yolk. Unfertilized eggs incubated without Me₂SO showed decreased levels of Na, Cl, and K in the zona radiata; fertilized eggs, incubated without Me₂SO showed decreased levels of Na, P, and Cl in the zona radiata and increased levels of K in the cytoplasm; unfertilized eggs, incubated with 10% Me₂SO showed decreased Na and Cl in the zona radiata, decreased K in the cytoplasm and increased K in the cortical alveoli; fertilized eggs incubated in buffer with 10% Me₂SO showed decreased levels of Na, P, Cl, and K (zona radiata), P, Cl, and K (cytoplasm), Na (yolk), and increased Cl in the yolk (all P<.01). Me₂SO (v/v) levels reached 1.5-3.1% in the zona radiata, 0-3.2% in cytoplasm, 2.3-8.7% in cortical alveoli, and 0-1.6% in the yolk. Unfertilized eggs showed more Me₂SO penetration than fertilized eggs.     

A unique surface pattern and micropylar apparatus in the eggs of Luciocephalus sp. (Perciformes, Luciocephalidae)

A hitherto undescribed Luciocephalus species was bred in captivity for the first time. The male mouthbrooders spawned about 80 slightly pear-shaped eggs with a diameter varying from 2-2 to 3-4 mm. The enveloping zona radiata measured 15 μm in thickness. In the SEM the outer surface of the zona radiata showed a pattern which is unique among all teleosts studied to date. Many of the numerous, virtually parallel ridges extended from the vegetal to the animal pole. There they spiralled towards the micropyle and terminated in its pit. The role of such a surface pattern as a sperm guidance system was discussed.     

SEM images reveal intraspecific differences in egg surface properties of common nase (Chondrostoma nasus L.)

Scanning electron microscopy (SEM) has been widely used to describe interspecific differences in egg quality of teleost freshwater fish, but potential intraspecific differences are poorly studied. Eggs of many rheophilic cyprinids are covered with adhesive structures such as attaching villi facilitating egg attachment at substrates of spawning grounds with high currents. Recent findings indicate that the egg quality of the rheophilic cyprinid common nase (Chondrostoma nasus L.), a target species of conservation, differs in the adhesiveness between spawning populations, potentially explaining differences in recruitment success. In this study, a SEM image-based standardized protocol was established to assess egg surface quality of Chondrostoma nasus eggs. Multivariate statistics detected significant differences of egg surface properties among individual females and among three different populations. These differences were mainly attributed to length variability and merging of adhesive villi as well as to coating and filament-like connections of these structures. The findings of this study highlight the need for further investigations to better understand the relationship of egg surface properties, egg stickiness and hatching success to understand the recruitment ecology and performance of early life stages in freshwater fish.     

Ultrastructural features of the egg envelope of silver carp, <Emphasis Type="Italic">Hypophthalmichthys molitrix</Emphasis> (Osteichthyes,Cyprinidae)

Synopsis We investigated the ultrastructure of the egg membrane surface (unfertilized egg) of Hypophthalmichthys molitrix using scanning electron microscopy. The eggs of silver carp like most other teleosts are surrounded by a relatively thick egg membrane, and have a type III micropyle at the animal pole. The micropyle is almost circular in shape and the micropyle canal is located in its center. The micropyle region is not flat. Round or oval accessory pores are also observed in the canal. The surface of zona radiata is wavy and uneven with a uniform distribution of almost round pores with lips. Microvilli like structure are found in the pore opening region.     

Reproduction and fecundity of tucunaré, Cichla kelberi (Perciformes: Cichlidae), an exotic species in Três Marias Reservoir, Southeastern Brazil

To evaluate the reproductive cycle and fecundity of tucunaré ( Cichla kelberi Kullander & Ferreira, 2006), 697 specimens were captured in Três Marias Reservoir, São Francisco River, Brazil during 1994–1995 and 2005–2006. Reproductive activity was recorded throughout the sampling periods, with females exhibiting asynchronous oocyte development and multiple spawnings with a peak in September–October. Vitellogenic oocytes of the tucunaré were elliptical in shape with the longest diameter approximately 1230 μm and the shortest 700 μm, yolk globules with ellipsoid inclusions, lipid vesicles, small cortical alveoli and thin zona radiata (9.3 ± 2.0 μm thickness). Follicular cells were prisma-shaped (49.0 ± 16.4 μm) in the vegetative pole, progressively becoming cubic cells in the animal pole toward the micropyle. Histochemical analyses indicated the presence of mucosubstances in the outer zona radiata and follicular cells that could be contributors to egg adhesiveness. Batch fecundity ranged from 4450 to 13 900 oocytes for females 31.5–43.5 cm total length, respectively, and correlated to gonadal weight ( r ² = 0.80) and body weight ( r ² = 0.70). Mean relative fecundity was 10.6 vitellogenic oocytes per gram body weight. As tucunaré is an exotic piscivorous species well-adapted to the Três Marias Reservoir, the present work may be considered a contribution toward future strategies for population control.     

A unique adhesion apparatus on the eggs of the catfishClarias gariepinus (Teleostei,Clariidae)

Eggs of the catfishClarias gariepinus were investigated for the first time using light and electron microscopy (SEM and TEM). In shape, they differ strongly from those of other teleosts, their characteristic profile resembling a fur cap. This shape is unique among the eggs of teleostean fishes. The eggs ofC. gariepinus are attached to substrata at their animal pole, which shows an annular bulge consisting of numerous tiny attaching-filaments. These filaments seem to be a part of the zona radiata externa. The micropyle, located within the center of the annular bulge, is a straight opening in the zona radiata. Different ways of egg adhesion in teleosts were compared and discussed as well as the position of the micropyle with respect to fertilization.     

The surface structure of Antarctic fish eggs and its use in identifying fish eggs from the Southern Ocean

Summary The surface structure of eggs of Notothenia neglecta, Nototheniops larseni, Nototheniops nudifrons (Nototheniidae), Champsocephalus gunnari and Chaenocephalus aceratus (Channichthyidae), collected near Elephant Island (Atlantic sector of the Southern Ocean) and of Notothenia rossii rossii (Nototheniidae) from Kerguelen waters (Indian sector of the Southern Ocean) was studied by scanning electron microscopy (SEM). Eggs of N. larseni differed from the other species by containing a micropyle with two micropyle pits. External morphological characteristics of the egg envelope such as the ultrastructure of the zona radiata, its interpore distances and the diameter of the micropyle were species-specific and could aid in the identification of fish eggs collected from the Southern Ocean.     

Fine structures of oocyte envelopes of three related cobitid species in the genus Iksookimia (Cobitidae)

Fine structures of the oocyte envelope (zona radiata) in three spined loaches, Iksookimia longicorpus, I. hugowolfeldi, and I. yongdokensis, are examined and compared. The zona radiata surrounding the oocyte is composed of two layers, a zona radiata externa, which comprised the outermost zona radiata (Z₁) of a homogeneous less electron dense single layer and the middle zona radiata (Z₂) of a homogeneous more electron dense single layer, and a zona radiata interna, which comprised the innermost zona radiata (Z₃) of heterogeneous electron-dense multilayers. Especially, the surface of the outermost zona radiata (Z₁) showed a morphological difference in its external appearance among the species. In the surface structures of Z₁, I. yongdokensis had a round granule appearance, and both I. hugowolfeldi and I. longicorpus were villus in morphology. In the villus appearance of these two species, however, there were clear differences between I. hugowolfeldi and I. longicorpus: the former had a few short thin villi, 1.0–1.7 μm in length, but in the latter species the villi were numerous, long, and thick, 2.0–2.5 μm long. The variety of such structures in these three species of Iksookimia may be a useful aid in taxonomic relationships and closely related to their habitats. Received: February 15, 2000 / Revised: August 3, 2000 / Accepted: September 3, 2000     

Biochemical and cellular insights into the temporal window of normal fertilization

Normal development depends on both the timing of fertilization and gamete quality, especially in assisted reproductive procedures. Recent studies of the proteins involved in the polyspermy block and cell cycle progression provide a cellular and biochemical basis for the short fertilizable lifespan of the mammalian egg in several species. Specifically, the status of cortical granules, zona proteins, cell cycle kinases, and intracellular calcium stores form a powerful panel of assays to monitor egg activation competence in eggs undergoing maturation and spontaneous activation events in mature eggs. An understanding of how these indicators are influenced by in vitro conditions and exogenous follicular stimulation should provide useful information for optimizing assisted reproductive procedures.     

The structure of the chorion of the egg of the mouthbrooding cichlid fish Tilapia mossambica

In Tilapia mossambica , the zona radiata of the chorion of the egg is greatly reduced and the gelatinous membrane is absent. These modifications can be correlated with the mouth-incubating habit of this species.     

Adhesive structures in the eggs of Corydoras aeneus(Gill, 1858; Callichthyidae)

The surface structure of the eggs of the catfish Corydoras aeneus was examined and showed to be a unique pattern among teleosts. The surface was covered with small protuberances, which resemble attaching‐filaments of teleost eggs. Eggs were, however, found to be very adhesive and since the species is known to inhabit turbid waters, this rare egg attachment mode could well be related to these environmental conditions.     

Cross-fertilization between Syrian and Chinese hamsters

The role of the zona pellucida in the specificity of fertilization was studied by cross-inseminations between Syrian (Golden) and Chinese hamster gametes. Cumulus-enclosed eggs from both Syrian and Chinese hamsters were placed together in one dish and inseminated with spermatozoa from either one or the other species. Fertilization always took place between gametes of homologous species. Chinese hamster spermatozoa failed to bind to the zona pellucida of Syrian hamster eggs; hence, fertilization was never observed. However, Chinese hamster spermatozoa could fertilize zona-free Syrian hamster eggs. In the reciprocal cross, a large number of Syrian hamster spermatozoa could bind to and penetrate the zonae of Chinese hamster eggs. However, fusion of Syrian hamster spermatozoa with the vitellus of zona-intact Chinese hamster eggs was never observed. After removal of the zona pellucida, only a small percentage (31%) of Syrian hamster spermatozoa could fuse with Chinese hamster vitelli. Thus, in these species, the mechanisms of interspecific gamete recognition and the prevention of interspecies fertilization seem to differ according to the direction of the cross. In Syrian hamster eggs, the block to interspecies fertilization seems to exist at the level of the zona pellucida, while in Chinese hamster eggs the block is at the level of the egg plasma membrane. The implications of these results in analyses of the genetics of spermatozoa, the molecular basis of sperm-egg recognition, and mechanisms of reproductive isolation leading to speciation, are discussed.     

Comparative morphology of the gonadal structure related to reproductive strategies in six species of neotropical catfishes (Teleostei: Siluriformes)

We studied the relationship between the morphology of the reproductive system and the reproductive strategies of six neotropical catfishes using macroscopic and microscopic analyses. The reproductive system of the examined Siluriformes showed diversified characteristics, but permitted their being grouped according to three reproductive strategies: pelagic spawning, demersal spawning, and internally fertilizing. The pelagic spawners Pseudoplatystoma corruscans and Conorhynchos conirostris have testes that are characterized by filiform lobes, absence of testicular secretion, full‐grown oocytes of small diameter, thin zona radiata, and cuboidal follicular cells. Pimelodus maculatus is morphologically distinct from the other two pelagic spawners catfishes due to the presence of testicular secretion. The demersal spawners Lophiosilurus alexandri and Rhinelepis aspera possess homogeneous testicular secretion, large mature oocytes, and columnar follicular cells. The most specialized reproductive system was observed in the internally fertilizing Trachelyopterus galeatus, which possesses a seminal vesicle accessory to the testes, spermatozoa with elongated nuclei that form spermatozeugmata, and a secretory ovarian lamellar epithelium that is associated with sperm storage. The reproductive system observed in Neotropical catfishes showed a relationship associated with the type of fertilization and the reproductive strategies of the six species studied. © 2011 Wiley‐Liss, Inc.