COMPOSITION OF THE BLOOD SERUM OF DEEP-SEA FISHES

¹ Department of Biology, Southeastern Massachusetts University, North Dartmouth, Massachusetts 02747

Serum osmolarity, chloride, urea, protein, and trimethylamine oxide were measured in 15 shallow water marine teleosts, 6 elasmobranchs, 9 deep benthic teleosts, and 24 midwater teleosts. Amino acids, carbohydrates, phosphate, and hematocrits were determined for some species from these four groups. Elasmobranchs had high osmolarity (1035 mOsm/l) because of high serum urea (363 mM/l), TMAO (66 mM/l), and chloride (295 mM/l). Shallow water teleosts had low osmolarity (444 mOsm/l), chloride (176 mM/l), urea (4 mM/l), and TMAO (14 mM/l). Deep benthic teleosts had higher osmolarities and chloride levels (576 mOsm/l, 242 mM/1) than shallow water teleosts, as did midwater teleosts (561 mOsm/l, 267 mM/1). Serum TMAO was high in benthic (51 mM/l), but not midwater (12 mM/l) teleosts, and urea was low in midwater (1.0 mM/l) and benthic (1.5 mM/l) groups. Stress and morbidity raise osmolarity and chloride in marine teleosts and may account for high values in midwater and benthic fishes, which were sampled after considerable trauma. The data suggest that deep-sea teleosts osmoregulate as do shallow water species, and do not support the notion that osmoregulatory specializations, such as ureosmotic regulation, evolve more rapidly in the deep sea. Very low serum proteins (0.8 g/100 ml) and hematocrits (< 10%) in midwater teleosts possibly relate to buoyancy or low metabolism.

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