Relationship between body density and feeding habit among flatfishes

The body density of 16 species of flatfish was measured. Their density varied, ranging from 1.011 to 1.074 g cm^-3, with benthic feeders tending to have the highest values, followed by mixed feeders and then pelagic feeders. Greenland halibut, Reinhardtius hippoglossoides, had the lowest value (1.022 ± 0.0052 g cm^-3), below the density of seawater (1.026 g cm^-3), indicating that this species can swim away from the sea floor with low-energy costs. In this manner, low body density may contribute to pelagic feeding. Further study of lipid content and other body characteristics of each flatfish is expected to elucidate their evolutionary traits more clearly.