Seasonal changes in thyroid hyperplasia, serum thyroid hormone and lipid concentrations, and pituitary gland structure in Lake Ontario coho salmon, Oncorhynchus kisutch Walbaum and a comparison with coho salmon from Lakes Michigan and Erie

Abstract

A progressive fall in serum thyroid hormone levels was found in Lake Ontario coho salmon, Oncorhynchus kisutch, between May 1978 and January 1979 concomitant with an increase in goitre frequency and thyroid hyperplasia. Despite marked differences in overt goitre frequency in sexually mature adult salmon collected from Lakes Ontario (43-7%), Erie (93,5Oh), or Michigan (O%), serum thyroid hormone levels and thyroid histology were similar in fish from the three lakes. Two gonadotrop-like basophil cells (' globular ' and ' vacuolar ') were found in the pituitary, particularly in sexually maturing and mature adults and 'jacks '.Whereas in salmon from Lakes Ontario or Michigan, the globular cells were vacuolated in Lake Erie salmon they were not; this observation may be correlated with the absence of obvious secondary sexual characteristics in Lake Erie salmon. Serum free fatty acids serum, triglycerides and cholesterol concentrations in Lake Ontario salmon fell progressively from the condition in fish collected from the Lake in May 1978, to that of fish collected during their potamodrous migration

Relationship between metabolic and reproductive hormones in salmonid fish

“…Such studies have been conducted on wild, migrating and captive stocks of fish. In Great O' l l 1_4;~4 Lakes coho salmon (Oncorhynchus kisutch), Leatherland and Sonstegard (1980) found higher plasma levels of T 4 and T3 in spring before maturation compared to those found during maturation in autumn. Decreases in plasma T 4 and/or T 3 have been reported during the seawater to freshwater transition, or during upstream migration and maturation of wild coho salmon (Sower and Schreck 1982), sockeye salmon (0. nerka; Biddiscombe and Idler 1983) and chum salmon (0. keta; Ueda et al 1984).…”

“…The elevated blood cortisol is undoubtedly important for mobilization of energy stores (protein catabolism, lipolysis, gluconeogenesis) during final maturation. In some salmonid species, blood concentration of thyroid hormones show complex patterns near the time of spawning (White and Henderson 1977;Osborn et al 1978;Leatherland and Sonstegard 1980;Pickering and Christie 1981;Sower and Schreck 1982;Biddiscombe and Idler 1983;Ueda et al 1984;). There is evidence that thyroid hormones may synergize with gonadotropin to promote ovarian steroidogenesis in goldfish (Hurlburt 1977), carp (Epler and Bieniarz 1983), freshwater perch (Sen and Bhattacharya 1981) and rainbow trout .…”

Effects of thyroid hormone on gonadotropin-induced steroid production in medaka, Oryzias latipes, ovarian follicles

“…However, there are discrepancies among profiles of circulating thyroid hormone levels during oocyte development. In salmonid and nonsalmonid fishes, high circulating levels of thyroid hormones were found before vitellogenesis, whereas, in salmonids, thyroid hormones decreased as maturation proceeded (brook trout, White and Henderson 1977; coho salmon, Leatherland and Sonstegard 1980; winter flounder, Eales and Fletcher 1982; Atlantic salmon, Dickhoff et al 1989). Decreases in T 4 and T 3 as spawning approached were also reported for brook trout (White and Henderson 1977) and rainbow trout (Osborn et al 1978), coho salmon (Sower and Schreck 1982), sockeye salmon (Biddiscommbe and Idler 1983) and chum salmon (Ueda et al 1984).…”

Variação periódica da triiodotironina (T3) plasmática e sua ação na reprodução induzida do matrinxã, Brycon cephalus (Günther, 1869) em cativeiro

“…Os hormônios tireóideos, desde longa data, têm sido relacionados à reprodução de vertebrados, incluindo os peixes (Hurlburt, 1977;Sower et al, 1985;Leatherland, 1987;Cyr & Eales, 1988, a, b;Dickhoff et al, 1989;Leatherland et al, 1989;Sullivan et al, 1989;Cyr & Eales, 1996;Holloway et al, 1999). A existência de receptores destes hormônios nas célu-las gonadais de diferentes espécies e anormalidades reprodutivas pela sua deficiência indica seu papel na fisiologia reprodutiva.…”

“…O efeito da temperatura na função tireóidea endógena em salmonídeos requer melhores esclarecimentos, embora estudos utilizando critérios radioquímicos tenham exibido aumento da atividade em altas temperaturas (Eales et al, 1991;Leatherland et al, 1980). Variações da temperatura que ocorrem ao longo do ano influenciam a função da tireóide em peixes (Eales & Brown, 1993).…”