Abstract
This paper reports on an evaluation of growth, gonadal development and reproductive endocrinology of older triploid (3 n ) European sea bass Dicentrarchus labrax in comparison with their diploid (2 n ) counterparts throughout their fifth and seventh annual cycle of life. While older triploids retained impaired reproductive endocrinology, a sexually related dimorphic growth was observed with 3 n females attaining the largest sizes. Comparisons of some body indexes showed that 3 n females had a significantly lower hepato‐somatic index ( I H ) than 2 n females but a significantly higher viscero‐somatic index ( I F ). In contrast, both male and female triploids showed significantly lower gonado‐somatic index ( I G ) than diploids. Accordingly, diploids produced mature gametes but triploids did not, demonstrating that despite the longer time given to triploids for gonadal development, they could not reproduce. Furthermore, older triploids had lower levels of plasma sex steroids (testosterone, T; 11‐ketotestosterone, 11‐KT and oestradiol‐17β, E 2 ) and luteinizing hormone (LH) than their 2 n counterparts with 3 n females showing drastic effects of triploidization on their reproductive endocrinology. Vitellogenin (VTG) was undetectable in 3 n females. Gonadal content of steroid hormones and Sparus aurata ‐type gonadotropin‐releasing hormone (sbGnRH) in the brain and pituitary were also lower in triploids compared with diploids. These results suggest that older 3 n D. labrax retain functional sterility in both sexes, and 3 n females might reach larger sizes than 3 n males and their 2 n counterparts in this species.