New Zealand Journal of Marine and Freshwater Research abstracts

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Rhythmic changes in plasma thyroxine concentrations

C. L. HOPKINS¹

W. A. SADLER²

¹Fisheries Research Division Ministry of Agriculture and Fisheries Private Bag 8324 Christchurch, New Zealand

²Nuclear Medicine Department Christchurch Public Hospital Private Bag Christchurch, New Zealand

Abstract Plasma concentrations of throxine (T₄) in chinook salmon, Oncorhynchus tshawytscha, rearing at a New Zealand salmon hatchery, were measured by radioimmunoassay. Blood samples for assay were collected at approximately weekly intervals during the period February-August (southern late summer-winter). Plasma T₄ levels varied in a cyclical fashion, with maximum concentrations occurring near the time of each new moon. Within the lunar month, the mean date of the recorded T₄ peak was at 6.4 + 3.9 days before new moon (95% confidence level). Since thyroid hormones have been implicated in the process of salmonid smol-tification, we suggest that the planning of hatchery release times for chinook salmon should include a component which takes account of the apparent link between lunar phase and circulating T₄ levels in these fish.

Keywords chinook salmon; Oncorhynchus tshawytscha; thyroxine; lunar rhythms; smoltifi-cation; hatchery rearing

New Zealand Journal of Marine and Freshwater Research, 1987, Vol. 21: 31-34 0028-8330/87/2101-0031$2.50/0 © Crown copyright 1987 received 12 december 1985

PDF file of entire paper: medium quality (340K); (scanned from paper original: notes about this process)

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