BIWEEKLY PATTERNS OF CHANGE IN FOOD-CONSUMPTION, PLASMA THYROID-HORMONE AND GROWTH-HORMONE LEVELS, AND INVITRO HEPATIC MONODEIODINATION OF T4 IN RAINBOW-TROUT, ONCORHYNCHUS-MYKISS

The purpose of this study was to examine whether the previously identified biweekly patterns of change in the growth rate of rainbow trout, Oncorhynchus mykiss, are associated with similar patterns of change in aspects of thyroid hormone and growth hormone physiology, and to continue to test the hypothesis that the lunar cycle may be serving as a Zeitgeber for the synchronization of this phenomenon. A significant biweekly pattern of change was observed for food consumption, plasma L-thyroxine (T4), triiodo-L-thyronine (T3) and growth hormone (GH) levels, liver protein content, hepatosomatic index, hematocrit, and in vitro hepatic monodeiodination of T4. The correlation of high and/or low levels of these values with the occurrence of new and full moons is discussed.