| Summary: | The role of muscle adipocytes in Atlantic salmon (Salmo salar) exposed to the water-soluble fraction-hydrocarbons (WSF-HC) of crude oil was thoroughly investigated by histologically examining the adipocyte and lipid distribution in different parts of muscle tissues, and by analyzing the WSF-HC in tainted adipocytes isolated from the muscle tissue and by analyzing the WSF-HC in different muscle tissues exposed to a series of WSF-HC concentrations. Belly flaps, subcutaneous fat layer, and myosepta in the muscle tissue were found to be the main sites for adipocytes. In muscle tissue proper, adipocytes were mainly distributed in myosepta and to a lesser extent in connective tissues surrounding bundles of white muscle fibers. Lipid droplets occurred in the connective tissue around bundles and individual dark muscle fibers, but were only occasionally occurred around individual white muscle fiber. Finely dispersed intracellular lipid droplets were present in dark muscle cells but were not observed in dorsal white muscle cells. Small adipocytes (20-40 $\mu$m) predominate in the adipocyte population in tissues of Atlantic salmon. Exposures of Atlantic salmon to both high levels of WSF-HC for a short period of time (8 h) and low levels of WSF-HC for a prolonged period (96 h) were carried out by using WSF-HC of Flotta North Sea crude oil rich in alkylated benzenes and by employing WSF-HC of K-D diluent, a commercial petroleum product rich in polycyclic aromatic hydrocarbons (PAHs). Atlantic salmon rapidly took up the WSF-HC in exposure water during both the 8 h and the 96 h exposure periods. Maximum concentrations of WSF-HC were reached after only 12 h of exposure in tissues having relatively lower lipid reserves (dorsal white muscle and dark muscle). It would take much more time (beyond 24 h) for tissues rich in lipids (subdermal fat tissue, mesenteric adipose tissue and belly flap) to attain equilibrium of WSF-HC between the tissue lipids and the exposure water. WSF-HC recovered from various tainted tissues were similar to those in the exposure water with respect to their relative abundance. Atlantic salmon were rapidly freed of most of the tainting WSF-HC (mainly alkylated benzenes of lower molecular weights) during the first 10 days of depuration in clean seawater, but the complete discharge of the remaining WSF-HC (mostly PAHs) from muscle tissue would take months. The depuration rates of accumulated WSF-HC were highly correlated with the lipid content of different muscle tissues and decreased as the molecular weights of individual WSF-HC increased. WSF-HC accumulated in the muscle tissue through the short-term exposure were depurated much faster than those accumulated through the long-term exposure. Prolonged starvation of the exposed Atlantic salmon did not help to accelerate the clearance of the accumulated tainting hydrocarbons from either whole muscle tissue or the subcutaneous fat tissue. After 96 h exposure of market-sized Atlantic salmon to 0.2 ppm WSF-HC, adipocytes isolated from the muscle tissue accumulated 14.3 times more WSF-HC (59.4 ppm) than the dorsal white muscle (4.2 ppm), while 54% of the tainting WSF-HC in the dorsal white muscle was found to be stored in associated adipocytes. (Abstract shortened by UMI.) Thesis (Ph.D.)--DalTech - Dalhousie University (Canada), 1996.
|
|---|