SummaryPseudoplatystoma coruscans is a very popular species for tropical fish culture as it has boneless meat of delicate taste and firm texture. Few studies on fish reproductive biology refer to the morphological features of eggs. The goal, therefore, of this present work was to perform a structural and ultrastructural analysis of fertilization and embryonic development in P. coruscans. The incubation period, from fertilization to hatching, lasts 13 h at 28/29• C and 18 h at 27• C. The oocytes had a mean diameter of 0.95 mm and hatched larvae were 2.55 mm in diameter. Analysing their development, we observed round, yellow oocytes that bore a double chorion membrane and a single micropyle. At 10 s after fertilization, several spermatozoa were detected attached to the oocyte surface. After 1 min of development, a fertilization cone that obstructed the micropyle could be observed. Segmentation started between 20 and 30 min after fertilization, when the egg cell was then formed. The first cleavage occurred between 30 and 45 min after fertilization, prior to reaching the morula stage (75 and 90 min after fertilization). The epiboly movement started at 120 and 180 min after fertilization and ended at 360 and 480 min after fertilization. Differentiation between cephalic and caudal region was detected after 420 and 600 min after fertilization and larvae hatched between 780 and 1080 min after fertilization. Seven main embryonic development stages were identified: egg cell, cleavage, morula, blastula, gastrula, segmentation with differentiation between cephalic and caudal regions, and hatching.
SummaryIn the present work, we analyzed the structure of oocytes and fertilized eggs of the piracanjuba fish (Brycon orbignyanus) under light and scanning electron microscopy. After inducing spawning, samples were collected at the moment of oocyte extrusion, when oocytes and semen were mixed (time 0), as well as at 10, 20 and 30 s after mixing, every minute up to 10 min, and then at 15 and 20 min. The oocytes are spherical, translucent and greenish with a mean diameter of 1.3 ± 0.11 mm. During the extrusion, cytoplasmic movement was observed in eggs towards the micropyle, characterizing the animal pole. At the moment of fertilization, the cortical cytoplasm showed a higher concentration of cortical alveoli at the animal pole than at the vegetal pole. The cortical alveoli breakdown promoted the elevation of the chorion with a consequent increase in egg diameter (1.95 ± 0.08 mm). The penetration of the spermatozoon promotes the formation of a fertilization cone of spherical external structure, which obstructs the opening of the micropyle. This structure acts as a main mechanism to avoid polyspermy, intercepting the access of supernumerary spermatozoa. Such studies about the reproductive biology of fish are important to species survival and conservation programmes.
The hybrid fish Pseudoplatystoma spp. has been raised on a large scale by several fish farmers, despite the fact that little is known about its biology. This is because it presents a number of zootechnical advantages over the parental species. In order to provide information about the early morphology of this important species, we analyzed the fertilization and embryonic development of the hybrid between spotted females and barred males of sorubim specimens by light microscopy and by scanning (SEM) and transmission electron microscopy (TEM) after induced spawning. Samples were collected at pre-established moments up to larval hatching. Seven distinct stages of hybrid embryonic development were identified: zygote, cleavage, morula, blastula, gastrula, histogenesis and organogenesis, and hatching. Under SEM, we observed spermatozoa at the micropyle entrance, the formation of a fertilization cone in the eggs, the differentiation of cephalic and caudal regions, the neural tube and embryo growth along the cephalo-caudal axis, as well as rudimentary optic vesicle and barbels. Under light microscopy, cytoplasmic movement was apparent with the consequent formation of animal and vegetative poles in eggs, in addition to epiboly movements and a small notochord portion. Under TEM, the oocyte chorion and eggs presented a sieve-like aspect in transversal cuts, coupled with the rupture of cortical alveoli and chorion elevation, thus enlarging the perivitelline space. Several mitochondria in the cortical cytoplasm were detected in both oocytes and eggs. Overall, we observed that the larvae hatched without visible morphological alterations, and seemed to be as viable in captive systems as they are in the natural environment.
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