A high-density linkage map and sex-linked markers for the Amazon Tambaqui Colossoma macropomum.

BACKGROUND: Tambaqui (Colossoma macropomum, Cuvier, 1818) is the most economically important native freshwater fish species in Brazil. It can reach a total length of over 1 m and a weight of over 40 kg. The species displays a clear sex dimorphism in growth performance, with females reaching larger sizes at harvest. In aquaculture, the production of monosex populations in selective breeding programmes has been therefore identified as a key priority. RESULTS: In the present study, a genetic linkage map was generated by double digest restriction-site associated DNA (ddRAD) sequencing from 248 individuals sampled from two F1 families. The map was constructed using 14,805 informative SNPs and spanned 27 linkage groups. From this, the tambaqui draft genome was improved, by ordering the scaffolds into chromosomes, and sex-linked markers were identified. A total of 235 markers on linkage group 26 showed a significant association with the phenotypic sex, supporting an XX/XY sex determination system in the species. The four most informative sex-linked markers were validated on another 206 sexed individuals, demonstrating an accuracy in predicting sex ranging from 90.0 to 96.7%. CONCLUSIONS: The genetic mapping and novel sex-linked DNA markers identified and validated offer new tools for rapid progeny sexing, thus supporting the development of monosex female production in the industry while also supporting breeding programmes of the species.

Embryonic development of teleost Brycon orbignyanus.

Brycon orbignyanus is an important large teleost that is currently on the list of endangered species, therefore studies on its reproductive biology and embryology are fundamental to help species conservation and recovery. The objective of this research was to characterize the events that occur during extrusion, fertilization and embryonic development of the species. The samples were collected at predetermined times, fixed and processed for light microscopy and scanning electron microscopy. The greenish oocytes were spherical, had translucent chorion and a mean diameter of 1.3±0.11 mm. The eggs had well defined animal and vegetative poles approximately 18 min post-fertilization. Stages from 2 to 128 blastomeres occurred between 20 min and 3 h post-fertilization (hPF), when the morula was characterized. The blastula stage was observed between 2 and 3 hPF, and the gastrula between 3 and 7 hPF, when the embryonic shield emerged and the cellular migration with the consequent formation of epiblast and hypoblast. At 8 hPF, the formation of the neural tube, above the notochord and the encephalic region, was observed, delimiting the forebrain, mesencephalon and rhombencephalon regions. From 11 hPF onward, the optic vesicle was formed close to the forebrain and the embryo tail was well developed. The optic vesicle was observed from 12 hPF onward, and the tail showed an intense movement that culminated with the rupture of the chorion and consequent hatching of the larva at 13 hPF and 27°C.