Abstract

Adult Procambarus clarkii (Girard, 1852) of either sex were air-exposed individually for periods of 1-12 h and 1 to 28 days in small opaque containers. Changes in haemolymph osmolarity, ammonia, oxygenation and acid-base status were monitored throughout. After 7 and 21 d air exposure, recovery was followed for 24 h in animals immersed either individually in 200 ml water in small containers (simulated burrow conditions) or communally in 100 litres water (simulated pond conditions). In air, haemolymph oxygenation was generally maintained or increased, but PCO₂ levels increased substantially. A slight initial respiratory acidosis was compensated within 3 days. Osmolarity declined only slightly but significant changes occurred in haemolymph [Na], [K], [Ca], [Mg], [Cu] and [Cl]. Analysis of these showed that marked changes of Strong Ion Difference accompanied both emersion and recovery. Ammonia levels increased in haemolymph. In recovery all hemolymph levels were reestablished quickly in simulated pond conditions but recovery was incomplete under simulated burrow conditions, especially after long-term exposure. P. clarkii in simulated burrow conditions rapidly removed O₂ from the water and rapidly excreted NH₃/NH₄⁺, CO₂ and perhaps other acidic equivalents which accumulated rapidly, both in the trapped water and in haemolymph. These crayfish thus tolerated very low levels of O₂ and high levels of CO₂, [H⁺] and NH₃/NH₄⁺ without apparent ill effects. These adaptations contribute to the ability of P. clarkii to survive the extensive periods of burrowing, including periods of air exposure, which may occur in their natural habitat.

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