Exogenous 17β‐oestradiol (E2) modifies thymus growth and regionalization in European sea bass Dicentrarchus labrax

The effect of 17β-oestradiol (E2) on the growth of the thymus and its regionalization into cortex and medulla was investigated in juvenile European sea bass Dicentrarchus labrax as they find themselves close to sources of oestrogenic pollution whilst residing in their estuarine nursery areas. While the exposure to 2, 20 and 200 ng l−1 in 60 days post-hatch (dph) fish tended to cause a non-monotonous dose–response curve with a significant difference of the cortex size between lowest and highest exposures, the exposure to 20 ng l−1 E2 from 90 dph onwards resulted in a distinct enlargement of the cortex. It is probable that the alteration of the cortex size also affects the T-cell differentiation and proliferation.