Extreme roll angles in Argentine sea bass: Could refuge ease posture and buoyancy control of marine coastal fishes?

The swim bladder provides a mechanism for buoyancy regulation in teleosts. However, in certain species, its location can result in an unstable body position, with associated energetic costs assumed for maintaining posture in addition to the energetic demands from swim bladder volume regulation. Direct observations show that some body-compressed, cave-refuging teleosts that nominally operate near neutral buoyancy may adopt unusual body attitudes within crevices. We hypothesize that these fishes may relax their buoyancy and posture control mechanisms during periods of rest. A prediction derived from this is that resting fish may adopt a wide range of roll angles (i.e., rotation about their longitudinal axis) inside caves. To quantify this behavior and for testing this hypothesis, triaxial accelerometers were deployed on free-living, cave-refuging Argentine sea bass Acanthistius patachonicus, and the relationship between roll angle and a proxy for activity (defined as the vectorial dynamic body acceleration, VeDBA) was analyzed. The results were compared with data available for three other species of fishes with disparate body forms and lifestyles: the pelagic whale shark Rhincodon typus, the dorsoventrally compressed benthic great sculpin Myoxocephalus polyacanthocephalus, and the fusiform and demersal Atlantic cod Gadus morhua. Inactive Argentine sea bass adopted a wide variety of roll angles, including extreme ones exceeding 80°, but had lower roll angles closer to an upright posture primarily associated with higher activity levels. In contrast, the great sculpin and Atlantic cod both rested at a close to upright roll angle but had higher activity levels associated with larger roll angles. Whale shark did not rest for the duration of the recorded period and also showed higher activity levels associated with larger roll angles. We propose that relaxation of buoyancy and posture control may help to reduce the metabolic rate in laterally compressed, cave-refuging fishes during periods of rest within crevices.Fil: Ciancio Blanc, Javier Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biología de Organismos Marinos; ArgentinaFil: Venerus, Leonardo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Trobbiani, Gastón Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Beltramino, Lucas Esteban. Universidad Nacional de la Patagonia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gleiss, Adrian C.. Murdoch University; AustraliaFil: Wright, Serena. Centre For Environment, Fisheries And Aquaculture Scien; Reino UnidoFil: Norman, Brad. Ecocean Inc; AustriaFil: Holton, Mark. Swansea University; Reino UnidoFil: Wilson, Rory P.. Swansea University; Reino Unid