Studies on cortisol, corticosterone, and 17b-estradiol indicate these
steroids have no role in stress or reproduction in the common octopus
(Octopus vulgaris)

The common octopus (Octopus vulgaris) is a promising candidate for aquaculture diversification, particularly in Europe. As interest in octopus farming grows, animal welfare concerns arise. In bony vertebrates (teleosts and tetrapods), measurements of the levels of corticosterone or cortisol have been successfully used as indicators of stress and welfare. Here, it is explored whether octopuses also produce cortisol or corticosterone and, if so, whether they are released into the water in response to stress (as can be done in teleosts and amphibians). The ability of the octopus to absorb cortisol from the water is also investigated-with another steroid, the principle vertebrate estrogen, 17 beta-estradiol (E-2), being used as a positive uptake control. In this study, using liquid chromatography tandem mass spectrometry techniques, it was found that octopus hemolymph did not contain either cortisol, corticosterone, cortisone (a common metabolite of cortisol), or E-2. Nor were any of the corticosteroids consistently found in the water in which stressed octopuses were held. The results support the evolutionary argument that octopuses are unlikely to exhibit a stress response mediated by vertebrate-like corticosteroids. Octopus demonstrated a low ability to absorb cortisol from the water (<2% over 24 h) but showed a high ability to absorb E-2 from water (92% over 24 h). In this latter respect, the octopus is similar to other mollusks. The finding calls into doubt the origin of the E-2 measured in this species. NEW & NOTEWORTHY This study demonstrates that common octopuses (Octopus vulgaris Cuvier 1797) do not produce cortisol, cortisone, or corticosterone in response to stress. Using liquid chromatography tandem mass spectrometry, it was also shown that octopuses have a low absorption rate of cortisol from water but a high absorption rate of 17 beta-estradiol (E2). The findings support the evolutionary argument that octopuses are unlikely to exhibit a stress response mediated by vertebrate-like