Comparative study on semen quality of one- and two-year-old ganders during the entire reproductive season

Aim: To evaluate the characteristics of semen produced by one- and two-years old White Italian ganders duringentire reproductive season, in order to clarify whether the young ganders are responsible for a low fertility rate in yougeese. Methods: Males were kept individually in cages under natural light. Semen was collected by dorso-abdonhal massage three times a week and routine examination was performed. Results: The mean ejaculate volume (2and 1.6 mL, respectively) and sperm concentration (323 and 281 × 10~6/mL, respectively) in one-year-old gandwere higher than those of two-year-old ones. The percentages viable spermatozoa of one- and two-year-old gandwere similar (91.4 and 92.3%, respectively), but the percentage of normally formed viable spermatozoa was signicantly higher in the older ganders than in the younger (47.8 and 42.9%, respectively, P < 0.05). Conclusion:The semina from one- or two-year-old Ganders were similar in regard to volume, sperm density and sperm motility,the percentage of normally formed viable spermatozoa, which is critical for fertilization, was significantly higher inolder ganders. It appears that the ganders are responsible for the low fertility rate in young geese.

Reproductive biology of Hemitripterus villosus in the Bohai Strait,China

To understand the reproductive biology of Hemitripterus villosus in the Bohai Strait,and fill the key knowledge gap in verifying reproductive seasonality and documenting gonadotropin dependent reproductive cycle of this species,a year-round detail study was conducted for the first time.In total,263 individuals were randomly sampled off the coasts of the Bohai Strait.Results show that and the overall female-to-male ratio(1.35:1)did not differ significantly from the 1:1 sex ratio.The length and weight relationship for females and males were regressed,depicting an isometric growth for both sexes.Four reproductive phases of the complete gonadotropin dependent reproductive cycle in both sexes were identified.The monthly variations in the gonadosomatic and hepatosomatic indexes for both sexes further indicated that this species spawns a single batch of eggs per year and the peak spawning period is from October to December.The average diameter of eggs ranged from 2.10 to 3.57 mm.The length at first sexual maturity was 224.87 mm for females and 241.26 mm for males.Significant positive relationships between absolute fecundity and fish size,and also gonadal weight were observed.H.villosus from the Bohai Strait exhibited smaller body size,smaller egg diameter,lower gonadosomatic index,lower absolute fecundity,and higher population extinction risk than the other populations’studied previously.Our findings contribute to understanding the status of this isolated westernmost population,and we emphasize that more efficient protection measures for the species and control measures are urgently required to improve the coastal environment in the Bohai Strait.

Changes of melatonin and its receptors in synchronizing turbot(Scophthalmus maximus)seasonal reproduction and maturation rhythm

In most fish,reproduction is seasonal or periodic under the suitable conditions.In turbot(Scophthalmus maximus)farms,one of the most economically important marine flatfish species,changes in daylength could cause changes in the spawning time.In this study,to characterize the regulation of reproductive physiology following light signals,three melatonin receptors(Mtnr)investigated in turbot were named sm Mtnr1,sm Mtnr2,and sm Mtnr1 c.Distinct expression profiles demonstrated that Mtnr m RNAs were concentrated in the brain(as detected in the hypothalamus(Hy)and mesencephalon(Me)),gonad and eye.The most abundant Mtnr1 and Mtnr2 m RNA expression levels were detected in the central nervous system at the beginning of the breeding season,suggesting that Mtnr1 and Mtnr2 may play vital roles in the regulation of turbot gonadal development.In addition,the melatonin profiles gradually increased and reached to the highest level at the spawning stage,indicating that melatonin is a potent hormone in the regulation of fish oocyte growth and maturation.The results of this study suggested that melatonin is the primary factor that transduces the light signal and regulates the physiological functions of turbot seasonal reproduction.Moreover,the results of this study may establish a foundation for further research seeking to identify fish melatonin receptors involved in the gonadal development and gamete maturation.