Zinc regulation in the freshwater crayfish (including some comparative copper analyses).

In the Plymouth area, estuarine decapod crustaceans like Carcinus maenas and Palaemon serratus have much higher concentrations of zinc in the blood than marine species such as Homarus vulgaris and Maia squinado. These differences between species with different powers of osmotic and ionic regulation have not been explained, but they were the starting-point of the present work. This is a study of the freshwater crayfish Austropotamobius pallipes pallipes (Lereboullet) to see whether adaptations to fresh water include modifications in zinc regulation. In Homarus and Carcinus the zinc concentrations in the body are controlled within fairly close limits. Unfed animals can achieve zinc balance when the concentration in the animal is more than io times that in sea water (Bryan, 1964, 1966, and unpublished). Balance is maintained by mechanisms regulating zinc absorption through the gills and zinc loss in the urine and across the body surface. Whereas in Homarus urinary losses of zinc are particularly important, losses across the body surface are more important in Carcinus. When animals are loaded with excess zinc, by feeding or by injection, the regulating processes become even more apparent. As Homarus is fairly closely related to the freshwater crayfish its method of zinc regulation has been used as a point of comparison throughout this work.