Expression of estrogen receptors in female rainbow trout (Oncorhynchus mykiss) during first ovarian development and under dense rearing condition

To study the expression of four estrogen receptor genes (er alpha 1, er alpha 2, er beta 1, er beta 2) of female rainbow trout (Oncorhynchus mykiss) during first ovarian development, trouts were sampled from different ovarian stages. Serum E-2 (estradiol) was measured by ELISA and estrogen receptors mRNA expression were examined by qRT-PCR. Our results showed a close association between increased er alpha 1 and vitellogenin mRNA expression during ovarian maturation and increased er alpha 2 mRNA expression in mature ovarian stages. Correlation analysis revealed that a negative relationship between serum E-2 and ovarian er beta 1 (or hepatic er beta 2), but ovarian er beta 2 mRNA expression was relatively unchanged during first ovarian development. Trout were also reared in different densities as stocking density 1, 2 and 3 (SD1, 4.6-31.1 kg/m(3); SD2, 6.6-40.6 kg/m(3); SD3, 8.6-49.3 kg/m(3)) to elucidate effects of high density on estrogen receptor expression. Histology observation showed ovarian development of trout in higher densities were retard with a relatively early stage and fewer vitellogenin accumulation. Trout in high densities showed significantly decreased serum E-2, er alpha mRNA expression and increasing trends of er beta mRNA expression. A noticeable increase of ovarian er beta 2 mRNA expression was seen in trout when density is approaching to 50 kg/m(3). In conclusion, we may hypothesize that increased er beta mRNA expression triggered by high density result in decreased er alpha mRNA expression and vitellogenesis. As a result, ovarian development in higher densities was retard. (C) 2017 Published by Elsevier Inc.