Seasonal and diurnal rhythms of thyroidal status in the rainbow trout, Salmo gairdneri Richardson

In order to study the relative importance of the feeding time and the light/dark alternation, as synchronizers of metabolic and endocrine parameters, the hepatosomatic index, liver glycogen contents, plasma glucose, nonesterified fatty acids, cortisol, growth hormone and thyroid hormone concentrations between dawn -2h and dawn + 12h are described in immature rainbow trout (Oncorhynchus mykiss). Trout were held in groups of 30 individuals and given access to a demand-feeder for only 3h per day, between dawn and dawn + 3h for 6 aquaria, and between dawn + 4h and dawn + 7h for another series of 6 aquaria. There was a clear effect of the time of food access on most of the studied parameters, with a decreased amplitude of variation, or a decreased mean level, in the fish eating in the middle of the photophase, compared with the fish eating at dawn. Superimposed on this apparent depressive effect of phase shifting of food access, some parameters also show direct responses to the shift of eating time, with a post-prandial increase or decrease.

Section: Discussionmentioning

confidence: 58%

Effect of restricted access to demand-feeders on diurnal pattern of liver composition, plasma metabolites and hormone levels in Oncorhynchus mykiss

Boujard

Brett

Lin

et al. 1993

“…Among other salmonid species, reported profiles of plasma THs during gonadal development are less contradictory. Plasma levels of T 3 and T 4 are highest before or soon after the onset of exogenous vitellogenesis and decrease as oocyte maturation proceeds (Osborn et al 1978;Leatherland and Sonstegard 1980;Sower and Schreck 1982;Biddiscombe and Idler 1983;Ueda et al 1984;Dickhoff et al 1989;Leatherland et al 1989a). Interestingly, in a congeneric of brown trout, Atlantic salmon (Salmo salar), plasma T 4 levels have been reported to increase during the latter stages of oocyte development (Dickhoff et al 1989), but this observation is complicated by the reported concomitant decrease in plasma T 3 levels.…”

Section: Discussionmentioning

confidence: 76%

Thyroid hormones in brown trout (Salmo trutta) reproduction and early development

Mylonas

Sullivan

Hinshaw

1994

Gravid brown trout (Salmo trutta) females were injected with various doses of a synthetic gonadotropin-releasing hormone analog (GnRHa), given with or without an injection of triiodothyronine (T3), in order to investigate the potential of T3 (a) to enhance the stimulatory effect of GnRHa on ovulation, and (b) to enhance the growth and survival of the produced progeny. From the time the hormonal treatments were initiated until ovulation was detected 5-38 days later, endogenous plasma T3 levels increased from an average of 3.6 to 11.6 ng ml(-1). Injection with 20 mg T3 kg(-1) body weight, further elevated plasma T3 levels at ovulation (16.0 ng ml(-1). Mean time to ovulation was reduced significantly in fish injected with 10 μg kg(-1) of GnRHa, whereas treatment with lower doses was ineffective. Injection with T3 did not enhance the ovulatory response of brown trout to GnRHa. Unfertilized eggs obtained from T3-injected females had a higher T3 content, suggesting a transfer of T3 from the maternal circulation into the oocytes. Maternal T3 injection had no effect on egg fertilization rates, embryo survival to eyeing and hatching, or the prevalence of abnormal larvae at the time of hatching. Length and weight gain of the progeny during yolk absorption was also not influenced by maternal T3 treatment. At the completion of yolk-sac absorption, progeny from females injected with T3 had a higher prevalence of skeletal abnormalities than controls. The results suggest that in teleosts like brown trout, which have high endogenous circulating T3 levels, treatment of females with T3 does not enhance responsiveness to GnRHa and it has the potential for deleterious effects on their offspring.

“…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). Decreases in T 4 and T3 as spawning approached were reported for non-anadromous brook trout (Salvelinusfontinalis; White and Henderson 1977) and rainbow trout (Salmo gairdneri; Osborn et al 1978). In captive salmonids, an increase in T 4 during the time of ovulation has been reported for brown trout (Salmo trutta; Pickering and Christie 1981).…”

Section: Discussionmentioning

confidence: 92%

“…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 .…”

Section: Introductionmentioning

confidence: 99%

Relationship between metabolic and reproductive hormones in salmonid fish

Dickhoff

Yan

Plisetskaya

et al. 1989

Circulating concentrations of estradiol (E2), vitellogenin (VTG), thyroxine (T4), triiodothyronine (T3) and insulin were measured in reproductively maturing four and five year-old Atlantic salmon. Blood samples were collected from the fish in seawater for one year prior to their spawning in November in fresh water. In females, E2 and VTG were low but detectable from December to July, and then increased to peak levels in September and October. Plasma levels of T4 and T3 were relatively constant in winter and spring, and decreased in July. Plasma concentration of T4 increased in November when the fish returned to fresh water. Plasma T3 levels remained low during the autumn. Both T4 and T3 levels tended to be higher in males than in females during September through November. Plasma insulin concentrations increased during the spring to peak values in May, and then decreased in June and July in fish of both sexes. There was a significant elevation of plasma insulin in males during October, and the levels in males tended to be higher than those found in females during final maturation.