Changes in blood hemoglobin, hematocrit, leucocrit, osmolarity, lactate, glucose and cortisol concentrations were monitored in common carp, Cyprinus carpio, exposed to decreasing temperatures (from 24°C to 4°C). Two experiments [rapid change (acute) and slow change (chronic)] were conducted. In the acute experiment, it took 3 days for the decrease of water temperatures from 24°C to 4°C. In the chronic experiment, it took 33 days for the decrease of water temperatures from 24°C to 4°C. Blood lactate and hemoglobin concentrations, hematocrit, and leucocrit significantly (P < 0.05) decreased in the cold-treated common carp in both experiments. Hemoglobin concentrations did not decrease until the temperature reached 4°C. Plasma glucose and cortisol levels increased in common carp in acute exposure to 4°C. The levels of plasma chloride and osmolarity did not change significantly (P > 0.05) in the cold-treated common carp in both acute and chronic exposure. Data indicate that levels of blood lactate, hematocrit, hemoglobin, and leucocrit were consistently responsive to the stress of low temperatures in common carp.
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Chen et al. (1996) studied this question.