“…For the killifish (Fundulus heteroclitus, Cyprinodontidae), the seasonal differences in the TSH-induced plasma T4 level were not explained by any alterations in plasma T4 clearance, supporting the view that the seasonal changes in TSH action probably occurred at the level of the thyroid tissue itself (Grau et al, 1985). Photoperiod, temperature, and salinity may in some instances modify teleost thyroidal sensitivity to TSH and TSH efficacy in the control of thyroid function (Olivereau, 1955;Delso and Flatin, 1956;Fontaine and Fontaine 1957;Lysak 1971a,b;Chart and Eales, 1976;Milne and Leatherland, 1980;Specker and Richman, 1984;Grau et al, 1985;Eales and Himick, 1991).…”