Embryonic development and larval growth of Brycon nattereri Günther, 1864 (Characidae) and its implications for captive rearing.

The aim of this study was to describe, for the first time, the embryogenesis and larval growth of the Paraitinga Brycon nattereri Günther, 1864 reared in captivity. After artificial fertilization, eggs were incubated at constant temperature (~19°C) and collected every 15 min during the first 3 h and then every 3 h until hatching. Five larvae were collected daily over 15 days for evaluation of the length, yolk sac volume and specific growth rate. The following stages of embryonic development were identified: zygote, cleavage, gastrula, segmentation and larval. The hatching occurred after 50-54 h, with larvae poorly developed and fully depigmented, devoid of mouth and swimming capacity, presenting 6.32 mm total length and 3.64 mm3 yolk sac volume. The mouth opening was observed between days 3-4 after hatching. The yolk sac absorption was slow during the first 3 days, increasing sharply after this period, being completed on the day 11. During this period there was a decrease in the larval growth rate. After yolk sac absorption, an increase in the growth rate was observed that coincided with the start of exogenous feeding. Cannibalism was not observed during the 15 days of evaluation. The initial development of B. nattereri was slow and poorly developed larvae in relation to other Brycon species, certainly due to the lower temperature required for egg incubation and larval rearing. Other studies are needed in order to develop techniques to improve the methods of incubating eggs and feeding larvae.

Methyl glycol, methanol and DMSO effects on post-thaw motility, velocities, membrane integrity and mitochondrial function of Brycon orbignyanus and Prochilodus lineatus (Characiformes) sperm.

The aim of this study was to use more accurate techniques to investigate the effects of cryoprotectants (CPAs) and extenders on post-thaw sperm quality of Brycon orbignyanus and Prochilodus lineatus. Six freezing media comprising the combination of three CPAs (DMSO, methanol and methyl glycol) and two extenders (BTS and glucose) were used. Sperm was diluted in each medium, loaded into 0.5-mL straws, frozen in a nitrogen vapor vessel (dry-shipper), and stored in liquid nitrogen at -196 °C. Post-thaw sperm motility rate and velocities (curvilinear = VCL; straight line = VSL; average path = VAP) were evaluated using a computer-assisted sperm analyzer. Membrane integrity and mitochondrial function were determined using fluorochromes. Post-thaw quality was considered high when samples presented the following minimum values: 60 % motile sperm, 140 µm/s of VCL, 50 % intact sperm membrane and 50 % mitochondrial function integrity. High post-thaw quality was observed in B. orbignyanus sperm frozen in BTS-methyl glycol and in P. lineatus sperm frozen in BTS-methyl glycol, glucose-methyl glycol and glucose-methanol. All samples frozen in DMSO yielded low quality. The presence of ions in the BTS extender affected post-thaw sperm quality positively in B. orbignyanus and negatively in P. lineatus. Methyl glycol was the most suitable CPA for both fish species, leading to a good protection of cell membrane, mitochondrial function and motility apparatus during the cryopreservation process. For an improved protection, B. orbignyanus sperm should be frozen in an ionic freezing medium.

Histochemical and morphological features of biopsied and stripped oocytes from the Brazilian endangered teleost pirapitinga, Brycon nattereri (Characiformes).

The aim of the present study was to characterize biopsied and stripped oocytes from the Brazilian endangered teleost pirapitinga (Brycon nattereri) using histochemical and morphological analyses. Biopsied oocytes had a mean diameter of 2.225 mm (modal diameter: 2.312 mm), complete vitellogenesis and a central or slightly eccentric nucleus. Neutral polysaccharides were detected in the follicular cells, zona radiata and yolk globules, while acidic polysaccharides were detected in the follicular cells and cortical alveoli. Ten out of the 19 females treated with two doses of carp pituitary extract (cPE) released oocytes, which were also analysed. Stripping occurred 292 ± 39 degree-hours after the second dose of cPE and led to a mean spawning weight of 36.2 g, 10% spawning index, 241 oocytes/g of ova, 8222 oocytes/female and 23 oocytes/g of body weight. Stripped oocytes had a mean diameter of 2.33 mm and a mode at 2.375 mm, were weakly adhesive and coloration ranged from wine to brown. Under scanning electron microscopy, stripped oocytes exhibited a single funnel-shaped micropyle located at the animal pole and a zona radiata that measured 7.7 µm in thickness with eight pore canals/µm2. Oocyte morphology in Brycon nattereri is similar to that found in other species of the genus, except for the larger size and weaker adhesiveness. These findings provide essential information for a better understanding of the reproductive biology of B. nattereri and the establishment of conservation measures for this threatened species.