Octopus welfare in aquaculture: study questions the use of cortisol as an indicator

The common octopus (Octopus vulgaris) is emerging as a promising species for aquaculture diversification, especially in Europe. Its biological and market potential is considerable. However, as interest in its farming grows, so do concerns about the welfare of these animals in intensive production systems. A recent finding, published in the American Journal of Physiology-Endocrinology and Metabolism, resulting from a collaboration between the Marine Research Institute (IIM-CSIC) in Vigo, the Centre for Environment, Fisheries and Aquaculture Science (United Kingdom), the Pescanova Biomarine Center (Spain), and the Centro de Ciências do Mar do Algarve (Portugal), challenges the traditional view that octopuses respond to stress through neuroendocrine mechanisms analogous to those of vertebrates.

Assessing animal welfare on the farm involves considering physical health, immune response, behavior, and, crucially, physiological indicators of stress. “In vertebrates, measurements of cortisol or corticosterone levels have been successfully used as indicators of stress and welfare,” explains CSIC researcher Josep Rotllant, from the Aquatic Biotechnology group (IIM-CSIC). “Therefore, it was important to explore whether octopuses also produce cortisol or corticosterone and, if so, whether they release them into the water in response to stress, as can occur in fish and amphibians.” The research was part of projects funded by the Centre for the Development of Industrial Technology (CDTI) and CSIC itself.

Why doubt corticosteroid hormones as stress indicators in octopuses?

From an evolutionary perspective, there are serious doubts about whether octopuses would use cortisol or corticosterone in the same way as vertebrates. Mollusks (the group to which octopuses belong) and vertebrates diverged about 670 million years ago. Furthermore, these hormones do not even function as stress steroids in the most primitive vertebrate classes, suggesting that their role in the stress response evolved much later in vertebrate history. Previous research and this new study the evolutionary argument that it is unlikely that octopuses exhibit a stress response mediated by corticosteroids similar to those of vertebrates. In fact, it has been shown that these organisms lack cortisol, corticosterone, or receptors homologous to vertebrate glucocorticoids, key molecules in the stress response in vertebrates.

Despite this biological improbability, several previous studies have attempted to measure these substances in mollusks. The present study, however, adopts a more specific and robust approach.

Seeking answers in the blood, water, and tissues of the octopus

To answer their questions, the researchers carried out a series of meticulous experiments with common octopuses (Octopus vulgaris) raised in captivity:

• Experiment 1: Are these hormones present in the octopus’s blood (hemolymph)? Scientists took hemolymph samples from octopuses (males and females) after they were subjected to acute stress. These samples were analyzed using advanced liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) to detect cortisol, cortisone (a metabolite of cortisol), corticosterone, and also 17β-estradiol (E2), the main vertebrate estrogen.
• Experiment 2: Do octopuses release these hormones into the water when stressed? Octopuses were placed individually in tanks after stressful handling, and water samples were taken at different intervals over 24 hours to measure the possible release of corticosteroids.
• Experiment 3: Can octopuses absorb these hormones from the water? Octopuses were exposed to water containing cortisol and E2 to assess their absorption capacity and the subsequent distribution of these hormones in different tissues. E2 was used as a positive uptake control.

A different hormonal landscape for the common octopus

The study’s findings are revealing:

• Absence of key corticosteroids: “It has been demonstrated, using advanced liquid chromatography coupled with tandem mass spectrometry techniques, that this cephalopod does not produce cortisol, corticosterone, or cortisone, hormones classically associated with both the stress response and osmotic regulation in vertebrates, especially in aquatic species facing salinity changes,” explains Rotllant. “The confirmation of the absence of these compounds in the hemolymph of these animals s the evolutionary hypothesis that octopuses, as mollusks, lack a stress response mediated by corticosteroids, which challenges the vertebrate models commonly used as a reference.”
• No consistent release into water: Stressed octopuses did not release detectable amounts of these corticosteroids into the water consistently.
• Low cortisol absorption capacity, high for estradiol: The study also highlighted that, although a low capacity to absorb cortisol from the aquatic environment was observed, octopuses showed high absorption of 17β-estradiol (E2), a behavior consistent with that observed in other mollusks.
• Absorbed E2 accumulates and is modified in the gills: The absorbed E2 was found mainly in the gills, largely esterified (bound to fatty acids).

Implications for aquaculture and octopus conservation

These results have profound implications that go beyond the laboratory:

• Vertebrate stress indicators are not extrapolatable: The main conclusion is that cortisol and corticosterone do not seem to play a similar role in the common octopus. Therefore, measuring these hormones in Octopus vulgaris to assess their welfare would not be a reliable strategy.
• Implications for osmoregulation and survival: The study investigated stress response mechanisms and possible osmotic regulation in the common octopus. According to Rotllant, “these results could shed light on the recent mass mortality of octopuses detected after heavy rains in the Galician rias, where freshwater input caused sharp drops in salinity.” He explains that “in species that do produce cortisol, this hormone plays a fundamental role in ionic regulation, allowing physiological adaptation to osmotic changes. The absence of this hormonal pathway in the octopus suggests a limited ability to respond to rapid decreases in salinity, which could seriously compromise their homeostasis and survival.”
• Relevance for aquaculture management and conservation: This finding not only expands knowledge about octopus physiology but also has key implications for its management in aquaculture and for the conservation of its populations in a context of climate change and increasingly frequent extreme events.
• Questioning of previous studies in mollusks: The study suggests that previous reports of corticosteroids in mollusks could be due to sample contamination or “false positives” generated by methodologies less specific than LC-MS/MS.
• The 17β-estradiol enigma: The high capacity of the octopus to absorb E2 from water and esterify it raises questions about the origin of E2 measured in octopus tissues in other studies. It could reflect the uptake of this steroid from the environment rather than endogenous synthesis with its own hormonal function.
• Urgency to find new welfare indicators for octopuses: It is crucial to intensify research to identify and validate stress and welfare biomarkers that are specific to cephalopods.

Conclusion

The study by Maskrey, Rotllant, and their collaborators represents a significant step forward. It demonstrates that Octopus vulgaris does not appear to use cortisol or corticosterone as stress hormones or for osmotic regulation as bony vertebrates do. These findings, stemming from solid scientific collaboration, are a call for caution and innovation for the growing octopus aquaculture sector and for conservation efforts. The industry and the scientific community must work together to develop new methods that allow for the reliable assessment of octopus welfare, ensuring that farming and management practices are sustainable and ethical, and considering their particular physiology in the face of environmental challenges such as salinity changes.

Josep Rotllant
Aquatic Biotechnology Laboratory, Instituto Investigaciones Marinas—CSIC
Vigo, Spain
Email: [email protected]

Reference (open access)
Maskrey, B. H., Costas, C., Méndez-Martínez, L., Guerrero-Peña, L., Tur, R., García, P., Touriñan, P., Chavarrias, D., Canario, A. V., Scott, A. P., & Rotllant, J. (2025). Studies on cortisol, corticosterone, and 17β-estradiol indicate these steroids have no role in stress or reproduction in the common octopus (Octopus vulgaris). American Journal of Physiology-Endocrinology and Metabolism. https://doi.org/E-00251-2024