EFFECTS OF SALINITY ON BLOOD OXYGEN CARRYING CAPACITY AND CHLORIDE CELL PROLIFERATION IN CYPRINODON VARIEGATUS

Cyprinodon variegatus is an extremely euryhaline and common coastal resident of the western Atlantic Ocean and Gulf of Mexico that in the wild has been found in ambient salinities ranging from freshwater (0 ppt) to salinities in excess of 140 ppt. The effects of salinity on chloride cell proliferation and growth, erythrocyte count, hemoglobin concentration, and hematocrit of individuals acclimated in the laboratory to salinities from 0 to 80 ppt was explored. Chloride cell density and height increased dramatically as salinity increased. Mean cell height increased from 7.25 μm in fish acclimated to 0 ppt to 18.4 μm in fishes acclimated to 80 ppt salinity. Similarly, chloride cell number (as measured by the number of chloride cells per 250 μm segment of gill filament) increased from a low of 1.1 cells in 0 ppt acclimated fish to 14.7 cells in fish acclimated to 80 ppt. These results correlated well with previously observed reductions in metabolism under hypersaline conditions. Salinity also had a significant effect on blood oxygen carrying capacity in C. variegatus, although differences were only noted at the very highest (60 to 80 ppt) and lowest (0 ppt) salinities tested. Salinity exerted the greatest influence on erythrocyte count and hemoglobin concentration, with values at 0 ppt and 60 through 80 ppt elevated in comparison to all other salinities. Hematocrit measurements were less dependent upon salinity, with highest values recorded in fish acclimated to a salinity of 0 ppt. Overall oxygen carrying capacity and all blood indices were also highest in fishes acclimated to 0 ppt salinity. Cyprinodon variegatus exhibited little change in erythrocyte count, hemoglobin concentration, and hematocrit over the range of salinities between 2 and 50 ppt, salinities that are most commonly seen in the Cedar Key salt marsh.