Behaviour of the Antarctic fish Ophthalmolycus amberensis (Zoarcidae) on gravel and muddy bottom

Abstract

The Antarctic zoarcid Ophthalmolycus amberensis occurs in Admiralty Bay (King George Island, South Shetlands) at 140 to 200m depth, where the bottom can be irregular, covered with gravel, or homogeneous, muddy, with fine sediment. In tanks, fish behaviour and adaptations to these two types of substrate were observed. The fish were active for less than 2% of the time an average, but individual variability was high. A circadian rhythm of motility was observed. They swam with rowing movements of the pectoral fins when on gravel, and with sinusoidal body movement when on muddy substrate. This resulted in significantly higher swimming speeds in fish on a muddy bottom, mainly at night, although bouts of swimming were more frequent on gravel. Their activity at night was higher for both substrates. Varied alert postures and alert for longer periods of time were observed on gravel than on muddy bottom. Fish exposed to muddy bottom fed more frequently and took greater amounts of food than fish on gravel, but failure in capturing in conjunction with rejection was higher than successful feeding. The capacity to make behavioural adjustments to the structure of the bottom allows O. amberensis to exploit efficiently different habitats at the sea bottom.