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

Abstract

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.

Leporinus elongatus induced spawning using carp pituitary extract or mammalian GnRH analogue combined with dopamine receptor antagonists

“…In this concern, future approaches that correlate maternal plasma E 2 levels with embryonic survival rates would be necessary to evaluate a possible maternal E 2 transfer to eggs which may cause toxicity to them. It has already been demonstrated that unbalanced maternal plasma reproductive hormones are transferred to eggs (Hwang et al, 1992;Mylonas et al, 1994) and are potential causes for embryo mortality in fish. There are also reports of higher E 2 and 17α, 20β-Dihydroxy-4-pregnen-3-one (17α, 20β-DHP) levels in non-viable eggs in relation to viable eggs (Feist et al, 1990).…”

Experimental test of the effect of maternal hormones on larval quality of a coral reef fish

“…Recent studies have suggested that developmental hormones transferred to the egg during gametogenesis govern development rates prior to the production of these hormones by the embryo (e.g., Schreck et al 1991;Hwang et al 1992; Barry et al 1995). Current evidence suggests a direct link between hormones in the maternal plasma and the eggs she produces, with developmental (e.g., thyroxine, triiodothyronine), reproductive (e.g., testosterone, estradiol) and metabolic (e.g., cortisol) hormones being transferred from female to egg (Brown and Bern 1989;Schreck et al 1991;Hwang et al 1992;Mylonas et al 1994). Two steroid hormones that are of particular interest from an ecological perspective are the corticosteroid, cortisol, which has been used as an endocrinological indicator of stress (Pankhurst and Van der Kraak 1997), and the male reproductive steroid, testosterone (Staub and De Beer 1997).…”

Evidence that thyroid hormone induces olfactory cellular proliferation in salmon during a sensitive period for imprinting

“…T 3 concentrations in fertilized eggs have been reported as high as 52·ng·g -1 body mass for salmonids (Mylonas et al, 1994), and maternal thyroid receptor transcripts have recently been identified in developing eggs and alevins (Jones et al, 2002). In addition, fluctuations in thyroid hormone have been linked to both hatching and emergence of fry from the gravel streambed Dickhoff and Sullivan, 1987;Leatherland et al, 1989;Hirano, 1987, 1989).…”