DOLPHIN THYROID AND ADRENAL HORMONES - CIRCULATING LEVELS IN WILD ANDSEMIDOMESTICATED TURSIOPS-TRUNCATUS, AND INFLUENCE OF SEX, AGE, AND SEASON

Biological and environmental influences on circulating adrenal and thy roid hormones were investigated in 36 wild and 36 semidomesticated Atl antic bottlenose dolphins, Tursiops truncatus, matched by age, sex, an d time of year when the samples were collected. Serum concentrations o f thyroxine (free [fT4] and total [tT4]), triiodothyronine (free [fT3] , total [tT3], and total reverse [rT3]), cortisol, and aldosterone wer e determined by radio-immunoassay. Wild female dolphins had significan tly higher levels of tT4, fT4 and fT3, an effect that was possibly rel ated to reproduction and lactation. Semidomesticated females had highe r tT3 than their wild counterparts. fT4 declined with age in wild dolp hins, whereas rT3 was greatest in the older animals. Cortisol and aldo sterone were both higher in wild animals sampled after a variable inte rval of up to four hours after encirclement by capture net. The patter n of adrenal hormone release suggested a mild stress response. Levels of both adrenal hormones were low in semidomesticated dolphins conditi oned to present voluntarily their tails for blood sampling, an approac h that appears to yield specimens representative of resting values for these constituents.