Expression characteristics of the cyp19a1b aromatase gene and its response to 17ß-estradiol treatment in largemouth bass (Micropterus salmoides).

To investigate the regulatory role of the cyp19a1b aromatase gene in the sexual differentiation of largemouth bass (Micropterus salmoides, LMB), we obtained the full-length cDNA sequence of cyp19a1b using rapid amplification of cDNA ends technique. Tissue expression characteristics and feedback with 17-ß-estradiol (E2) were determined using quantitative real-time PCR (qRT-PCR), while gonad development was assessed through histological section observations. The cDNA sequence of LMB cyp19a1b was found to be1950 base pairs (bp) in length, including a 5' untranslated region of 145 bp, a 3' untranslated region of 278 bp, and an open reading frame encoding a protein consisting of 1527 bp that encoded 508 amino acids. The qRT-PCR results indicated that cyp19a1b abundantly expressed in the brain, followed by the gonads, and its expression in the ovaries was significantly higher than that observed in the testes (P < 0.05). After feeding fish with E2 for 30 days, the expression of cyp19a1b in the pseudo-female gonads (XY-F) was significantly higher than that in males (XY-M) (P < 0.05), whereas expression did not differ significantly between XX-F and XY-F fish (P > 0.05). Although the expression of cyp19a1b in XY-F and XX-F fish was not significantly different after 60 days (P>0.05), both exhibited significantly higher levels than that of XY-M fish (P<0.05). Histological sections analysis showed the presence of oogonia in both XY-F and XX-F fish at 30 days, while spermatogonia were observed in XY-M fish. At 60 days, primary oocytes were abundantly observed in both XY-F and XX-F fish, while a few spermatogonia were visible in XY-M fish. At 90 days, the histological sections' results showed that a large number of oocytes were visible in XY-F and XX-F fish. Additionally, the gonads of XY-M fish contained numerous spermatocytes. These results suggest that cyp19a1b plays a pivotal role in the development of ovaries and nervous system development in LMB.

Genetic diversity analysis and development of molecular markers for the identification of largemouth bass (Micropterus salmoides L.) based on whole-genome re-sequencing.

Largemouth bass (Micropterus salmoides L.) is generally considered to comprise two subspecies, Florida bass (M. floridanus) and Northern Largemouth bass (M. salmoides), which have biological characteristic differences because of their geographical distribution. In this study, whole-genome re-sequencing was performed among 10 Florida and 10 Northern largemouth bass, respectively. In total, 999,793 SNPs and 227,797 InDels were finally identified, and 507,401 SNPs (50.75%) and 116,213 InDels (51.01%) were successfully mapped to annotated 18,629 genes and 14,060 genes, respectively. KEGG classification indicated that most of these genes were focused on the pathways including signal transduction, transport and catabolism, and endocrine system. Genetic diversity analysis indicated that Florida largemouth bass had higher genetic diversity than Northern largemouth bass, indicating that the germplasm quality of Northern largemouth bass had markedly reduced in China. To examine the accuracies of the identified markers, 23 SNPs and eight InDels (the insertions or deletions of more than 45 bp) were randomly selected and detected among Florida largemouth bass, Northern largemouth bass, and their F1 hybrids. The detection efficiencies of all the markers were higher than 95%; nineteen SNPs and three InDels could accurately distinguish the two subspecies and their F1 hybrids with 100% efficiencies. Moreover, the three InDel markers could clearly distinguish the two subspecies and their F1 hybrids with a PCR-based agarose gel electrophoresis. In conclusion, our study established a simple PCR-based method for the germplasm identification of largemouth bass, which will be useful in the germplasm protection, management, and hybridization breeding of largemouth bass.

Timing of early gonadal differentiation and effects of estradiol-17ß treatments on the sex differentiation in Largemouth bass (Micropterus salmoides).

In this study, an efficient estradiol-17ß (E2)-induced feminization method was established based on the timing of early gonadal differentiation in Largemouth bass (Micropterus salmoides). Histological section results showed that from 20 days post-hatch (dph) to 30 dph, the germ cells gradually differentiated into oogonium and spermatic deferent, respectively. Moreover, female-biased genes Foxl2 and Cyp19a1a were up-regulated to the first peak at 20 dph, while the male-biased genes Dmrt1 were up-regulated to the first peak at 30 dph. These results indicated that the timing of early gonadal differentiation in Largemouth bass was between 20 and 30 dph. Therefore, 15 dph Largemouth bass with a body length of 15.10 ± 0.09 mm were chosen, and four E2-treated diets were set as 0 (E0, control), 50 mg/kg E2 (E50), 100 mg/kg E2 (E100), and 200 mg/kg E2 (E200). After feeding with E2-treated diets for 60 days, female ratios were 55%, 100%, 100%, and 100% in E0, E50, E100, and E200 groups, respectively. No intersex fish were observed in all the groups. However, 30% of females in the E200 group possessed thinner ovaries, with smaller ovary cavity structures and a decreased number of primary oocyte cells than those in other groups. Besides, the Largemouth bass in the E0 group grew more than those in E50, E100, and E200 groups during the E2 treatments period (P < 0.05). In conclusion, our study suggested that 50-100 mg/kg E2-treated diets could effectively induce the feminization of 15 dph Largemouth bass within 60 days duration time, which provided valuable information for the breeding of the all-male Largemouth bass population.

Optimization of conditions for the cryopreservation of yellow catfish (Pelteobagrus fulvidraco) sperm.

Yellow catfish (Pelteobagrus fulvidraco) is a promising aquaculture species in China with an increasing market demand. To serve the growing demand of male broodstock for artificial fertilization and the preservation of valuable strains for selective breeding, we tried to develop a species-specific cryopreservation protocol for yellow catfish sperm in this study. Important factors such as cryoprotectant, freezing height above the liquid nitrogen (LN) surface, dilution ratio, equilibration time, thawing temperature and cool storage before freezing were standardized. Among the cryoprotectants tested here, 10% Me2SO was the most suitable for sperm cryopreservation. Freezing at 7 cm above the LN surface for 10 min yielded the highest post-thaw motility. Further evaluation showed that dilution ratio of 1:3 and 1:5 produced higher post-thaw motility than semen diluted at 2:1, 1:1, 1:9 or 1:19. Equilibration times from 0 to 30 min did not cause significant differences in both equilibrated and post-thaw motility. Also, cool storage up to 24 h did not affect the suitability of sperm for cryopreservation. After thawing, sperm could be stored at 4 °C for 2 h without a reduction in motility parameters. With the combination of optimized freezing conditions, the fertilization and hatching rate of cryopreserved sperm were 87.1 ± 5.2% and 78.5 ± 7.4%, respectively, which were similar to those of fresh sperm (91.8 ± 3.5% and 83.7 ± 2.5%). In general, the cryopreservation protocol optimized here would facilitate breeding practice and hatchery operation in this economically important fish.