The effect of oxygen on the growth of Oncorhynchus mykiss embryos with and without a chorion

Growth was measured in dechorionated and chorionated embryos of rainbow trout Oncorhynchus mykiss exposed to three oxygen treatments: hypoxia, normoxia and hyperoxia (nominally 5, 10 and 15 mg 1(-1)). Dechorionated embryos grew faster than chorionated ones in all three oxygen treatments. Similar patterns. however, were found in both dechorionated and chorionated groups; embryos exposed to hypoxia grew less than normoxic and hyperoxic exposed embryos. Moreover, there was no significant interaction between the effect of oxygen levels and presence or absence of the chorion on growth after hatching. These results suggest that the effect of oxygen on growth was not affected by the presence of the chorion. (c) 2005 The Fisheries Society of the British Isles.