A note on seasonality in anoxia tolerance of crucian carp (Carassius carassius (L.)) in the laboratory

Young crucian carps from a natural pond were enclosed in jars with anoxic water and the survival times at different temperatures were recorded. Considerable seasonal differences in the survival times were demonstrated. The year of the crucian carp can be divided into three periods. 1) the reproductive period in spring and early summer. This starts from the melting of the ice (in April — May) and during its first three weeks the high tolerance to anoxia is lost. 2) the start of reserve build up from late summer to autumn is further characterized by only short survival (approx. 1 day) in anoxia. Then, accompanied by a final accumulation of winter reserves (glycogen), a longer survival time of up to 10 days or more at low temperatures is attained. 3) wintering is the period characterized by very long survival times in anoxia. The tolerance of juveniles (age group 0+) seems to develop a month or two later than that of older fish. The long survival times (up to 4.5 months at +3°C) in winter are suggestive of even longer tolerance to natural anoxia at the low temperatures prevailing in local ponds.