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Abstract

Respiration, ammonia excretion and decompression tolerance were studied in several species of lysianassoid amphipods captured at four stations in the deep Arabian Sea with an isolated trap maintaining them at in situ temperature. The amphipods were decompressed from their ambient to atmospheric pressure during recovery. Six amphipods, belonging to the species Eurythenes gryllus, Paralicella caperesca and Abyssorchomene abyssorum, survived decompression from depths between 1920 and 4420 m. The physiological condition of these specimens was good inferred by the fact that their swimming and resting behaviour appeared normal, they reacted to disturbance by light and vibration, and were able to ingest food to maintain full guts. Most of the amphipods (421 individuals), however, were recovered dead, which allows information about their decompression tolerance and their vertical migration ability to be deduced. Weight- specific respiration rates of the deep-sea amphipods that were fed prior to the experiments were not lower than in shallow- water amphipods living at similar temperatures. Differences in respiration rates between the specimens are discussed with regard to body size, species specificity and food supply. Weight-specific ammonia excretion rates were extremely high when compared with shallow-water relatives, indicating a capability for rapid digestion. This may be an adaptation to the unpredictable food supply in the deep sea as it enables the amphipod to empty its digestive tract quickly, thus making it available for additional food. Rapid digestion also enables the animals to regain mobility soon after feeding, permitting them to move to new food sources. (C) 2002 Elsevier Science Ltd. All rights reserved.