Dorsal aorta catheterization in rainbow trout (Salmo gairdneri) I. Its validity in the study of blood gonadotropin patterns.

The use of a dorsal aorta catheterization technique to study gonadotropin secretion patterns in the rainbow trout was tested. Heparin used to flush the cannula between repetitive samplings did not have any effect on plasma GTH levels. Catheterization resulted in a slight short-term change in those levels. The gonadotropin levels returned to their initial values as soon as 30 min to 6 hrs after the operation. From then on, the GTH levels remained close to the initial values in fish exhibiting normal feeding behaviour, whereas they tended to decrease in "stressed" females which did not eat normally. The fish which adapted well to dorsal aortic catheterization did not show any changes in the diurnal pattern of GTH levels or in normal gonadal function and GTH profiles during the processes of oocyte maturation and ovulation. It is concluded that individual catheterized trout can be used advantageously for studying gonadotropin secretion patterns after a 3-day recovery period and the elimination of those fish which neither resume normal feeding nor return to initial, pre-operative GTH levels. Using this technique, it was demonstrated that hypophysial GTH release in trout with oocytes undergoing active vitellogenesis is probably effected by short-term bursts (pulses) of secretion.