Environmental physiology of the teleostean thyroid gland: a review

Abstract

SynopsisRecent studies of thyroid hormone function are reviewed as they relate to the environmental physiology of teleost fish. In addition, reports dealing with the apparent interdependence of thyroid gland function with that of other endocrine glands are discussed with emphasis on the interrelated endocrine response associated with changing physiological status of teleosts.Seasonal changes in thyroid gland activity are described in several species. Although seasonal alterations in apparent thyroid status are concomitant with changes in ambient temperature, photoperiod and/or gonadal status, their biological significance is not fully understood and direct relationships are for the most part, not proven. Similarly, most reports of thyroid involvement in gonadal development or maturation are based on indirect evidence of the relationship. The exception to this is a study in immature or hypophysectomized goldfish in which thyroxine (T4) was shown to promote ovarian development and maturation, possibly acting collateralistically or synergistically with gonadotropin. Even in this study it is not clear whether the Td effect is a direct action on the ovarian tissue or an indirect action via the regulation of metabolites necessary for gonad metabolism. Integumentary silvering and retinal porphyropsin formation in salmonids are stimulated by administration of T4 or thyroid extracts. Administration of T4 or triiodothyronine (T3) enhances skeletal and somatic growth in some teleostean species, although the effect on somatic growth is most pronounced when these hormones act synergistically with somatotropin (STH) or androgens. The growth-promoting effects of T4 and T3 may be linked to their apparent involvement in lipid, carbohydrate, protein and vitamin metabolism. Alterations in apparent thyroid activity concomitant with changes in ambient temperature have been reported (for example correlated with seasonal ambient thermal changes), although there are marked contradictions in data presented by different investigators. Reported temperature-related effects on thyroid function are probably secondary responses of thyroid metabolism to altered temperatures. Evidence of a direct rate of thyroid hormones in the regulation of migration (and associated behavioural modifications), salmonid smoltification, oxygen consumption, and osmotic or ionic regulation although highly suggestive in a number of areas is inconclusive and requires further critical experimental evaluation.The pituitary control (by thyrotropin) of thyroid secretion of T4 is convincingly shown in several teleosts, and Receivrd 26.6.1980 Accepted 6.12.1980 0 Dr W. Junk Publishers, The Hague. Printed in The Netherlands. 0378.1909/82/0071-0083 $03.4083 evidence of an inhibitory hypothalamic control of thyrotrop activity is highly suggestive in some species. A thyrotropic effect of somatotropin preparations is well established in several teleostean species; the effect does not appear to be related to contamination of the somatotropin preparations with thyrotropin, and ma...

Effects of hexazinone and atrazine on the physiology and endocrinology of smolt development in Atlantic salmon

“…Food deprivation can lower thyroid activity in teleost fish (Leatherland, 1982;McCormick and Saunders, 1990), but in the present study, plasma T 4 and T 3 levels were only affected in smolts exposed to 100 g l −1 ATZ after 24 h SW challenge. In salmon, thyroid hormones are involved in several aspects of smolt development including migration, morphological changes and imprinting (Hoar, 1988), but there is little evidence that thyroid hormones have a direct role in controlling salinity tolerance in salmonids (McCormick, 2001).…”

“…In salmon, thyroid hormones are involved in several aspects of smolt development including migration, morphological changes and imprinting (Hoar, 1988), but there is little evidence that thyroid hormones have a direct role in controlling salinity tolerance in salmonids (McCormick, 2001). The response of the thyroid axis to changes in environmental salinity appears to be highly variable (Leatherland, 1982), and the precise nature of the interaction between ATZ and SW exposure in affecting the thyroid axis will require further investigation.…”

Effects of Ozonation on the Speciation of Dissolved Iodine in Artificial Seawater

“…17,23,33,35 Other factors, including the presence of goitrogens, may alter iodine metabolism and availability and subsequently affect thyroid health. 9,21,30,34 An aquatic environment can contain a variety of suspected goitrogenic compounds, including ammonia, urea, nitrates, nitrites, and established chemical toxins.…”

“…4,10,[12][13][14]17,23,24,31,34 In general, fish thyroid hormone metabolism mimics that of most other vertebrates. 32,35 In bony and cartilaginous fish, thyroid metabolism and thyroid disease 30 are affected by dietary and environmental 9,22 iodine levels.…”

“…32,35 In bony and cartilaginous fish, thyroid metabolism and thyroid disease 30 are affected by dietary and environmental 9,22 iodine levels. 23,32 Studies of the chemical form of iodine that is used in teleost or cartilaginous fish thyroid metabolism are scarce. 7,17,24 Iodide (I Ϫ ) is required for the synthesis of thyroid hormones tri-iodothyronine (T 3 ) and thyroxine (T 4 ) in fish 4,17,24 and other vertebrates.…”