Glucocorticosteroids, the missing molecules of the building blocks of octopuses' stress response

XIV Congress of the Iberian Association of Comparative Endocrinology, Bilbao, 11-13 September 2023Currently, the common octopus (Octopus vulgaris) is a promising candidate for diversifying aquaculture in Europe. Its rapid growth, adaptability to captivity, and high nutritional and economic value make it attractive for meeting market demand and reducing pressure on wild populations. However, octopuses’ complex characteristics, particularly their sensitivity to environmental factors and need for specific nutritional requirements, present significt challenges for intensive farming. Fortunately, the once-difficult obstacle of high mortality rates during the rearing phase has been overcome, enabling the industrialscale cultivation of these animals. As interest in octopus aquaculture continues to grow, concerns arise regarding the potential impacts of large-scale production and intensified farming practices on the welfare of the animals. Assessing farm animal welfare typically involves evaluating physical health, immune response, behavior, and physiological indicators, with a particular focus on identifying stress levels. Therefore, understanding how to recognize signs of stress, establish reliable stress biomarkers, and effectively manage stress levels is essential for successful domestication and farming of these creatures. In vertebrates, the production of glucocorticosteroids (GCs) is a key response to stress. These are hormones that regulate energy balance and overactivity of the immune response. Their blood levels are widely used as a reliable indicator of stress in vertebrates. However, the mechanisms underlying the stress response in invertebrates, and especially cephalopods, are still poorly understood. In this study, we demonstrate that octopus hemolymph does not contain either of the major GCs that regulate the stress response in vertebrates. Furthermore, as found in a fish and another mollusk, the blue mussel, we show that the octopus has a poor ability to absorb GCs from the water (