Hormones vs. environment: How fish tolerate constant change

University of Hawaiʻi
Daniel Woo looking into microscope
Graduate student Daniel Woo of CTAHR’s Department of Human Nutrition, Food and Animal Sciences.

Many fish live in variable environments, meaning they must constantly adapt to changes in water salinity, temperature and chemical content (i.e., pollutants). How a fish responds-in order to keep surviving, growing and reproducing-is of deep interest for scientists and commercial aquaculture producers who rely on controlled environments.

Ongoing work in the University of Hawaiʻi at Mānoa College of Tropical Agriculture and Human Resources (CTAHR) may provide some clues.

CTAHR investigators are doing research on three fronts, helping to better understand:

  1. How fish hormones mediate the impact of a rise in temperature.
  2. How the actions of these hormones are affected by age.
  3. How chemicals and pollutants released in the environment can interfere with fish growth and reproduction.

“Our NSF-, NIH– and NOAA-funded projects are targeted to better understand how specialized cells can sense the environment, respond to environmental change, and regulate functions essential for survival, such as salt-and-water balance, as well as functions essential for animal production, such as growth and reproduction,” said principal investigator Andre Seale of the Laboratory of Fish Endocrinology and Environmental Physiology, part of CTAHR’s Department of Human Nutrition, Food and Animal Sciences (HNFAS).

Detecting salinity changes

The mechanisms responsible for how fish detect changes in salt concentration may be at play when fish respond to a rise in temperature, noted HNFAS graduate student Daniel Woo. He recently presented the evidence at the 45th annual Albert L. Tester Memorial Symposium and the 6th Biennial Conference of the North American Society of Comparative Endocrinology.

“This is because the cells that play an important role in detecting changes in salinity, through changes in volume and release of the hormone prolactin, also increase in volume and prolactin release when the temperature rises,” explained Seale.

Affected by age?

Are cells that make those adjustments, in response to environmental changes, affected by age? In a new study, “Age-dependent decline in salinity tolerance in a euryhaline fish,” Seale and collaborators make the case that age does affect those cells, at least in regard to changes in salinity. Their study appears in Frontiers in Aging.

“Older fish have a lower capacity to survive a transfer from freshwater to seawater,” he said. “The ability to acclimate between widely changing salinities is a key characteristic of the Mozambique tilapia, a fish commonly used in aquaculture due to its environmental resilience. At least partly underlying this decline in salinity tolerance is a reduction in the responsiveness of older fish to the hormone, prolactin.”

Introduced chemicals

In a review of “endocrine-disrupting chemicals”-chemicals and pollutants that cause adverse effects in organisms by disrupting the actions of hormones-Research Specialist Fritzie Celino-Brady presents a comprehensive analysis of the experimental approaches used for investigating their effects on fish growth and reproduction. Celino-Brady’s article, “Experimental approaches for characterizing the endocrine-disrupting effects of environmental chemicals in fish,” appears in Frontiers in Endocrinology.

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