Meeting Abstract
The family Liparidae, snailfishes, span the largest depth range of any marine fishes. The shallowest species can be found in tidepools of temperate zones, while hadal snailfishes, the deepest-living fishes, reside as deep as ~8,200 meters. Extreme environmental conditions—low temperature, high pressure, lack of light, limited food availability, and varying oxygen concentrations—exert evolutionary pressures on the organisms that inhabit the deep sea. Liparids do not have swim bladders and are mostly demersal, but the deepest species must maintain neutral buoyancy to spend time in the water column hunting for their sparse prey. Reduced bone density is another mechanism by which these species adapt to maintain buoyancy in the deep sea. We used micro computed tomography (micro-CT) scanning to study bone density across the full bathymetric range of the Liparidae, 32 species from 12 genera. Of these specimens, five bones were measured for density by calculating relative mean pixel brightness to hydroxyapatite phantoms: the lower jaw, for purposes of feeding mechanics; the third vertebrae, as a control; the first left pelvic pterygiophore, for studying the suction disk; the hypural plate, to study swimming and movement trends, and the sagittal otoliths. Taking into consideration the phylogeny of the specimens, we observed a decrease in bone density with increasing depth. The degree of change in density with depth differed among the structures that we measured, with evolutionary implications for functional performance of structures in the deep sea.
