P2.120 Thursday, Jan. 5 Proximate chemistry of buoyant gel tissues in benthopelagic and benthic deep-sea fishes GERRINGER, M.E.**; FRIEDMAN, J.; DRAZEN, J.C.; YANCEY, P.H.; Whitman College, Walla Walla; Univ. of Hawai'i, Honolulu; Univ. of Hawai'i, Honolulu; Whitman College, Walla Walla firstname.lastname@example.org
It has long been known that the muscles of some deep-sea animals have high water and low protein contents, hypothesized to be an adaptation to low food availability or reduced intensity of visual predator-prey interactions. Some mesopelagic fishes also have a gelatinous layer beneath the skin and/or around the spine, hypothesized to be a buoyancy adaptation. Several demersal species also have similar layers, though their composition and function have not yet been fully described. This study characterized these layers in seven species from Monterey Bay Canyon (1,000 to 3,000 m): 4 benthopelagic (Bothrocara brunneum, Careproctus melanurus, Careproctus cypselurus, Spectrunculus grandis), 2 benthic (flatfishes Embassichthys bathybius, Microstomus pacificus), and a new species of eelpout Pachycara n sp. A (habitat uncertain). We determined osmolalities and tissue buoyancies and conducted proximate chemistry analyses for contents of water, sodium, potassium, protein, carbohydrate, lipid and organic osmolytes including trimethylamine oxide (TMAO). We found that gel in all species had high water content, 94.8-98.7%. Sodium, potassium and TMAO concentrations were similar to plasma (rather than muscle) of similar species. Protein (average 0.5%), carbohydrate (average 0.6%) and lipid contents were low in all species. All gel tissues floated in cold seawater while muscle tissues sank for all but the new eelpout species, in which both gel and muscle floated. These results are consistent with the buoyancy hypothesis. Lift may benefit flatfishes during burst swimming. The composition may also be a way to increase body size with low energy costs. The low nutritive content of this tissue may have commercial implications for the fishing industry.