Anoxia survival in common carp and crucian carp is related to high zinc concentration in tissues

Ten lots of common carp and six lots of crucian carp (each lot of 100 fish) were treated under anoxia for five days at water temperatures of 25-31 degrees C. The average per group mortality of common carp was 17%, but none of the 600 crucian carp died. The digestive tract tissues of the common carp that died had significantly lower zinc concentrations than those that survived (59 +/- 41 vs 142 +/- 60 mu g/[g fresh tissue], P < 0.001). The digestive tract tissues of the crucian carp had mean zinc concentrations of 652 +/- 458 mu g/(g fresh tissue). One lot of common carp that had low tolerance for anoxia was fed a high zinc diet (2000 mg zinc/kg diet) for 1, 2 or 6 months and then subjected to 5 days anoxia. The survival rates of those fed the high zinc diet 1 and 2 months increased from 0 to 50%, respectively; all of fish that had fed a high zinc diet for 6 months survived. Thus, anoxia survival in common carp and crucian carp is closely related to the high concentrations of zinc in their tissues.