Critical partial pressures of oxygen causing precocious hatching in Coregonus lavaretus and C-albula embryos

Embryos of whitefish (Coregonus lavaretus) and vendace (C. albula) were exp osed to various hypoxic conditions at constant temperatures of 8 degreesC a nd 11 degreesC at the developmental stages of "eye movement visible" and "f irst embryos hatched". Eggs exposed to hypoxia responded with precocious hatching and the response depended on the degree of hypoxia, test temperature, and developmental pha se. The calculated critical partial pressures of oxygen (pO(2)) causing pre cocious hatching at 8 degreesC were 40 mm Hg (3.0 ppm dissolved oxygen conc entration-DO) for whitefish and 28 mm Hg (2.1 ppm DO) for vendace embryos. The sensitivity of embryos to hypoxic stress increased rapidly as developme nt progressed. Eventually, the critical pO(2) for vendace eggs increased to 81 mm Hg (6.0 ppm DO) at the stage of "first embryos hatched". Higher temperatures caused stronger response of embryos to hypoxia: exposur e of whitefish embryos for 60 min to pO(2) of 3 mm Hg (0.2 ppm DO) at 8 deg reesC resulted in hatching of 43% of eggs, whereas at 11 degreesC, hatching increased to 95% (at the same oxygen concentration). Adequate DO concentra tions must be provided in incubation to prevent early hatching and increase d mortality. (C) 2001 Elsevier Science B.V. All rights reserved.