We study the temporal variation in amount of progesterone-like substance in
tissuesof the fiddler crab, Uca vocans borealis. Both HPLC and radioimmuno
assay (RIA) were employed to determine the amount of a progesterone-like su
bstance in extracts of ovary and hepatopancreas. The results show that, dur
ing the breeding period (egg-carrying, January-September), the progesterone
-like substance concentrations in ovaries and in hepatopancreases of the cr
abs studied were 13.8-29.3and 7.7-17.2 ng per gram of tissue, respectively;
while the values dropped to 1.0-2.1 and 4.8-6.8 ng per gram of tissue, res
pectively, during the nonbreeding period (non-egg-carrying, October-Decembe
r).