COLLEGE STATION -Biologists have discovered that longer days make redfish grow faster. This discovery could have far-reaching consequences on fish culture techniques aimed at increasing fish growth and improving their quality.
Duncan S. MacKenzie, a Texas A&M University professor of biology, and Kevin Leiner, a zoology graduate student, made this discovery while studying the workings of the thyroid gland in redfish and how it affects their behavior and metabolism.
The thyroid gland releases a chemical, thyroxine, which regulates fish growth and metabolism - the way fish receive and use energy.
"Although we still do not know exactly how the thyroid regulates fish growth, the work we have done indicates that animals that are happy and healthy and are growing very actively have very high thyroid hormone levels," says MacKenzie.
Although thyroid activity in mammals is quite high, the first scientists who measured thyroid hormones in fish found very little. So it initially was assumed that thyroid hormones play a minor role in fish metabolism.
"We discovered that, in fact, thyroid hormone is very dynamic in some fish species like the redfish," says MacKenzie. "The hormone is very precisely regulated, its level increasing and decreasing regularly at different times of the day."
Since 1995, MacKenzie has been investigating the mechanisms of thyroid hormone regulation in redfish. He has been mainly interested in the effects of food intake and light exposure on thyroid hormone release.
MacKenzie has conducted experiments involving large fish tanks sampled at different times. In each experiment, lasting between two to eight weeks, the amount of light, food, and the times of day that fish are fed have been precisely controlled.
For each experiment, Leiner measured the daily redfish thyroid hormone levels by taking blood samples every two hours. At the end of each experiment, the fish are examined in order to determine the amount of fat and muscle
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Contact: Keith Randall
kr@univrel.tamu.edu
979-845-4644
Texas A&M University
18-Mar-2001