Fish Hormones Change When Oxygen Is Scarce. (Sexual Hang-Up)

By Morgan, K. | Science News, March 1, 2003 | Go to article overview

Fish Hormones Change When Oxygen Is Scarce. (Sexual Hang-Up)


Morgan, K., Science News


Oxygen deprivation tampers with sex hormones in fish and impairs reproduction, according to new research. The results suggest that low oxygen in freshwater ecosystems can disrupt animals' endocrine systems. Researchers say this link might explain the ongoing decline in some fish and amphibian species.

Various pesticides, components of plastics, and other chemical pollutants known collectively as endocrine disruptors mimic natural hormones such as estrogen. Scientists have linked such contaminants to reproductive failures in many animals and to oddities ranging from deformities in frogs to sex changes in fish. The disruptors are also suspected of underlying some breast cancer in women.

Researchers have found that other physical factors--including artificial lighting and magnetic fields--can similarly disrupt hormones (SN: 7/3/93, p. 10). Now, Rudolf S.S. Wu of the City University of Hong Kong and his colleagues add oxygen deficiency, or hypoxia, to the list of endocrine disruptors.

Human activities that overload fresh water with plant nutrients, such as components of fertilizers and detergents, reduce concentrations of dissolved oxygen in lakes and rivers. Wu and his colleagues found earlier that oxygen-starved fish have an altered metabolism and remain smaller than normal. The team wondered whether the almost suffocating conditions might also stunt fish reproduction.

To find out, the team placed immature adult carp--a species unusually tolerant of hypoxia--in lab conditions of either normal or one-seventh normal oxygen concentrations for 12 weeks. …

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