Resistance to Zinc Sulphate of Zebrafish (Brachydanio rerio) Embryos After Removal or Rupture of the Outer Egg Membrane

Abstract

Fifteen- and 25-hr-old zebrafish (Brachydanio rerio Hamilton-Buchanan) embryos with the outer egg membrane ruptured survived longer in a solution of zinc sulphate (20 ppm Zn) than embryos of the same ages with the membrane intact. Forty-two-hour embryos with the membrane completely removed survived in four concentrations of zinc sulphate (2.5, 5, 10, and 20 ppm Zn) at least as long as 42-hr embryos with the membrane entire. The high resistance of zebrafish embryos to zinc was therefore not owing to protection by the membrane. On the contrary the presence of the membrane lowered resistance.This result was probably owing to the formation of opaque material enclosed by the outer egg membrane of zinc-poisoned, unruptured eggs. The action of this material in reducing survival is unknown.