Inhibition of Ovarian Growth by Cadmium in the Fiddler Crab, Uca pugilator (Decapoda, Ocypodidae)

The effect of cadmium chloride (1 mg/L) on oocyte growth of the fiddler crab, Uca pugilator, was studied during the slow vitellogenesis phase of ovarian maturation of this carb. In vivo experiments were done with both intact and eyestalkless crabs. The intact cadmium-exposed crabs exhibited a significantly lower oocyte diameter than the controls at the end of the 2-week exposure period, but no significant differences were detected among the eyestalkless crabs, suggesting that the effect of cadmium could be on the sinus gland in the eyestalks, increasing secretion of the gonad-inhibiting hormone (GIH). To test this hypothesis, in vitro experiments were done, incubating pieces of ovary with and without eyestalk tissue, in the presence of thoracic ganglion, needed for oocyte growing due to the secretion of the gonad-stimulating hormone (GSH). Only when eyestalk tissue was present in the incubation media was oocyte growth inhibited by cadmium compared to the controls. These results strongly suggest that cadmium acts at least in part to increase the secretion of GIH from the sinus gland. GIH could then in turn act by (a) inhibiting secretion of GSH by the thoracic ganglion, (b) directly inhibit the oocytes, or (c) both (a) and (b).