natural endocrine profiles of the groupliving skunk anemonefish amphiprion akallopisos in relation to their sizebased dominance hierarchy groupliving animals commonly display differences in behaviour physiology and endocrine profiles between conspecifics within the group which are tightly linked to reproduction teleosts exhibit a variety of social systems where social status as well as sex has been linked to different androgen and oestrogen profiles levels of gonadal androgen and oestrogen were investigated as a function of sex and position in a social hierarchy in freeliving individuals of the skunk anemonefish amphiprion akallopisos a protandrous pomacentrid fish with a sizebased dominance hierarchical social system plasma levels of 11ketotestosterone 11kt testosterone t and 17oestradiol e2 as well as conversion ratios from t were measured by elisa from 111 individuals along a linear hierarchy from 38 social groups in the wild blood plasma levels of 11kt and e2 showed sex differences being higher in males and females respectively as expected based on their role as the major androgen and oestrogen in fish reproduction however no sex differences were found for t which may represent its role in territorial defence or simply as a precursor for the synthesis of 11kt and e2 in terms of the hierarchical social system within males 11kt levels decline as the hierarchy is descended which may represent their decreasing reproductive opportunity as well as the decreasing levels of aggression towards males lower in the hierarchy in summary the sizebased dominance hierarchy is associated with distinct steroid levels of 11kt and e2 between individual freeliving a akallopisos that closely resemble those of species in which breeding individuals suppress reproduction of conspecifics lower in the hierarchy