Consequences of air exposure on the physiology and behavior of caught-and-released common carp in the laboratory and under natural conditions

Specialized anglers of Common Carp Cyprinus carpio in Europe and increasingly in North America usually release trophy-sized fish, often following retention in carp sacks, to facilitate photographic memories. This practice is associated with extended air exposure. We assessed the impact of air exposure for a period of 10 min after capture and after an additional 9 h of retention in carp sacks on the physiology of small carp at two water temperatures (12°C and 22°C) under laboratory conditions. In a complementary field experiment with large carp, we also assessed the effects of air exposure on their physiology and additionally assessed the effects on tissue damage, postrelease behavior (i.e., movement and time rested), and survival. In the laboratory, plasma lactate increased by 24% during air exposure following simulated capture, and blood pH dropped by 0.16 units relative to a capture-only situation. Other physiological variables were unaffected by the treatment. In the field, air exposure after capture did not affect any physiological variables or indicators of tissue damage. During retention in carp sacks, fish recovered from capture, but subsequent air exposure caused a plasma lactate rise of 358% in the laboratory and 89% in the field experiment, and blood pH dropped by 0.38 units in the laboratory relative to that for the retained fish. In the field experiment, postrelease movement was significantly reduced in air-exposed fish, but normalized within 12 h. No mortalities occurred within 2 months postrelease. From a fish welfare perspective, our results suggest that photography should be conducted directly following capture without further retention in carp sacks as this approach is less deleterious to the fish. However, there is no benefit in doing so for maintaining carp populations because no substantial mortalities are to be expected. Overall, Common Carp are highly resilient to even extended air exposure.