This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Cortisol is a hormone that helps humans and many other animals regulate their energy use and respond to changing conditions. For a long time, sharks and rays were believed to rely on a different steroid hormone for these functions, without producing cortisol themselves.
Now, a new study of North Pacific spiny dogfish, a species of small shark, challenges this view. Researchers at the University of Manitoba and Bamfield Marine Sciences Center in Canada detected cortisol in the sharks' blood following experiments involving diluted seawater or antibiotics. The team's paper, published in Proceedings of the Royal Society B, also offers molecular evidence hinting at the sharks' ability to produce cortisol.
Their findings concern one species, leaving open whether this ability extends to other sharks and rays. The idea that sharks and rays lack cortisol emerged from research in the 1960s and 1970s. Scientists identified a similar steroid hormone, called 1α-hydroxycorticosterone, and suggested that earlier cortisol measurements may have mistakenly detected this other hormone.
To reduce the risk of mistaking this other hormone for cortisol, the team separated components in dogfish blood samples using high-performance liquid chromatography before measuring hormone levels. An independent analysis using liquid chromatography with tandem mass spectrometry confirmed cortisol in two samples. In one experiment, dogfish collected off British Columbia were placed in diluted seawater for 48 hours and subsequently returned to normal seawater.
Before exposure, the team detected cortisol in only one shark. Among five sharks monitored throughout recovery, all had detectable cortisol after 36 hours, while only one did at 72 hours. Average concentrations did not differ significantly across the recovery times included in the statistical analysis.
This intermittent detectability could explain why earlier studies missed the hormone. The researchers also examined the interrenal gland, an organ that produces steroid hormones. They identified molecular messages for an enzyme involved in synthesizing cortisol, further supporting a possible production pathway, but did not yet test whether the enzyme is active in the tissue.
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