The influence of water temperature on the induction of vitellogenin in walleye pollock Gadus chalcogrammus

Abstract

This study examined the influence of water temperature on the induction of vitellogenin (VTG) in walleye pollocks (Gadus chalcogrammus) in aquaculture. The full-length VTG-A (or VTG-I) gene of walleye pollock was cloned using RACE (Rapid amplification of cDNA ends)-PCR method from liver tissue and recombinant VTG protein (wpVTG) was expressed in E. coli. The wpVTG protein was used to construct polyclonal antibodies to specifically detect VTG in blood; the antibodies were verified using western blotting. The VTG in blood plasma was determined by ELISA. The relationship between GSI (gonadosomatic index), VTG and body length were all positively correlated, and the results indicated that VTG can be used as an indicator of sex and/or maturation of female G. chalcogrammus in aquaculture. When VTG was measured in by the aqua-cultured female pollocks raised in water temperature of 5 °C, 8 °C, 11 °C, and 14 °C, VTG was detected only at 5 °C and 8 °C. In the histological analysis of VTG-inducing individuals, vitellogenesis was found in ovaries. In those same samples, E2 (17beta-estradiol) was detected in the blood by LC-MS. On the other hand, there was no significant difference in level of VTG induction when E2 of same concentration was treated to hepatocyte culture in different water temperatures. These results seemed to indicate that VTG is not directly affected by water temperature. However, we considered that the water temperature indirectly affect VTG induction by affecting the E2 concentration level.