Age-dependent hepatic mRNA expression levels of vitellogenin (VTG) gene in Siberian sturgeon Acipenser baerii as determined by RT-qPCR assay. (A) Vitellogenin expression levels in females sampled over a period of 7 months (7M) to 4 years (4Y) of age. At the age of 4 years, the average expression level in females showing the apparent advance of ovarian maturation from the appearance in the 3Y-individuals is labeled as 4Y-I, while the expression level in 4Y-females exhibiting only similar ovarian appearance with 3Y-fish is indicated as 4Y-II. The label 4Y-P indicates the average with pooled data without distinguishing 4Y-I from 4Y-II. Means with different letters are significantly different based on ANOVA followed by Duncan’s multiple range tests at p < 0.05. Numbers in parentheses are percent coefficient of variation values. The coefficient of determination (R2) and the corresponding equation are also provided on the upper left of the graph. (B) Expression levels in males. Regimes for labeling and statistic evaluation are same as in (A). Additionally, the closed triangle indicates the significantly higher level of vitellogenin mRNA expression in males compared to that in same-aged females, based on Student’s t-test (p < 0.05). On the other hand, the significantly lower expression level in males compared to that in females is indicated by inverted closed triangle (p < 0.05). (C) Expression levels in fully matured females and males at ages of 7 and 8 years (7Y-F and 8Y-F for females while 7Y-M and 8Y-M for males). Individual expression levels of two hermaphroditic intersex fish (ITS-1 and ITS-2; 7-year-old) are also presented.