BUOYANCY STUDIES AND MICROSCOPY OF SKIN AND SUBDERMAL EXTRACELLULAR-MATRIX OF THE ANTARCTIC SNAILFISH, PARALIPARIS-DEVRIESI

The Antarctic snailfish Paraliparis devriesi (Liparididae) occupies an epibenthic habitat at a depth of 500-650 m in the subzero waters of M cMurdo Sound, Antarctica. Although lacking a swim bladder, this specie s is neutrally buoyant through the combined effects of reduced skeleta l ossification and expansion of a watery gelatinous subdermal extracel lular matrix (SECM). The SECM serves as a low density buoyancy agent. It comprises a mean of 33.8% of the body weight, the largest known pro portion of any adult fish. The SECM is loose connective tissue dominat ed by ground substance consisting of glycosaminoglycans, especially hy aluronic acid, and immobilized water. Although the SECM is 97% water, elevated levels of NaCl provide an osmotic strength greater than that of other body fluids. Only small amounts of antifreeze compounds have been identified in P. devriesi; therefore, freezing avoidance may resu lt from the combined effects of antifreezes and the elevated osmolalit y of body fluids. The skin overlying the SECM is thin (85-200 mum) and loose, and unlike most other fishes, the epidermis is several times t hicker than the dermis. The midepidermis, has a distinctive layer of v acuolated club cells of unknown function. Light and electron microscop y indicate that the skin. is unspecialized for protection against entr y of ice. (C) 1994 Wiley-Liss, Inc.