How Fish Live Under High Pressure

Many deep-sea fish can live under high pressure not because pressure “does not act” on them, but because their water-rich tissues lack large gas cavities that would compress strongly with depth. Pressure inside fluids and tissues largely balances the outside pressure. Gas-filled swim bladders are often absent in deep-sea species or replaced by other buoyancy strategies—gelatinous tissue, lipids, or specially adapted bladders. In some groups, bones are less mineralized; this can lower body density and help with buoyancy, but it is not a universal “armor” against pressure.