The concentrations of thyroxine (T4) and triiodothyronine (T3) in the blood plasma of rainbow trout (Sulmo gairdneri Richardson) at intervals throughout the year have been measured by a chemically specific gas-liquid chromatographic (GLC) method. Mean hormone levels showed a seasonal variation, maximal levels of both hormones occurring in winter and minimal concentrations in mid summer. An apparent secondary maximum in mean T4 and T, concentrations was observed in spring. (T4)/(T8) ratios have been found to be highest in winter and lowest in summer. A radioimmunoassay procedure, validated by GLC analyses, revealed the presence of a diurnal rhythm in serum T4 levels of trout sampled in September and in April.

No abstract

A chemically specific analysis for plasma thyroid hormones has been used to disclose a seasonal bimodality in the concentrations of thyroxine (Tp) and triiodothyronine (Ts) in the plaice; maxima in both hormone levels occur in winter and in summer. The ratio of T, concentrations to T, varies seasonally being at a minimum in summer. A highly significant correlation of T, plasma levels with the landings per unit fishing effort for the same area has been observed.

No abstract

opening of the tapered tip, thereupon the stopcock of the reservoir is closed. The lower trap then cuts off suction of gas through the right-hand tube. If the system were perfectly gas-tight at con-