Ocean life
Dogfish blood reveals unexpected hormone
Canadian scientists discovered traces of cortisol in spiny dogfish sharks, challenging decades of biological assumptions about marine predators.
Reported by Phys.org · · 1 min read
Scientists have identified cortisol in the bloodstream of North Pacific spiny dogfish, questioning a long-standing belief that sharks and rays do not use this common steroid hormone. For decades, researchers assumed these marine creatures relied entirely on an alternative chemical known as 1-alpha-hydroxycorticosterone, suspecting that older measurements had confused the two compounds.
To prevent misidentification, a research team from the University of Manitoba and the Bamfield Marine Sciences Center analyzed blood collected from dogfish off British Columbia using advanced chromatography and mass spectrometry. Their tests confirmed the presence of genuine cortisol following specific environmental and medical interventions.
In one trial, sharks spent two days in diluted seawater before being placed back into standard marine conditions. While nearly all individuals showed no detectable hormone initially, every monitored shark had measurable amounts after thirty-six hours of recovery. Because these levels fluctuated and dropped again after three days, scientists suspect the hormone's fleeting presence explains why earlier investigations failed to observe it.
Examining production pathways
The investigators also inspected the animals' interrenal gland, which generates steroids. They discovered genetic material encoding an enzyme linked to cortisol synthesis, pointing toward an internal production pathway, though whether the tissue actively deploys this enzyme remains unverified.
Another test involved feeding the sharks antibiotics or saltwater through a tube for several days. Cortisol appeared only in the antibiotic group several days after treatment concluded. The authors had hypothesized that resident microbes might normally degrade the hormone before it circulates widely, though high fat concentrations in the tissue prevented them from proving bacterial disruption.
Finally, researchers administered cortisol implants to observe bodily changes over three days. The treated sharks displayed reduced blood glucose compared to a control group, indicating a potential role in metabolic regulation. The findings open new questions about whether other elasmobranch species share the capacity to synthesize the hormone.
