Role of adipocytes in the muscle tissue of Atlantic salmon (Salmo salar ) in the uptake, release and retention of water-soluble fraction of crude oil hydrocarbons

Abstract

The uptake and depuration of the water-sol‐uble fraction (WSF) of hydrocarbons of crude petroleum by Atlantic salmon (Salmosalar) has previously been examined in terms of whole muscle. The hypothesis that the tainting WSF in the muscle was retained primarily by adipocytes has been investigated by the isolation of adipocytes and the subsequent analysis for hydrocarbons in adipocytes. After 96 h exposure of market-sized Atlantic salmon to 0.2 ppm WSF, adipocytes isolated from the belly flap region of the muscle tissue accumulated 14.3 times more WSF (59.4 ppm) than the dorsal white muscle (4.2 ppm), while 54% of the tainting WSF in the dorsal white muscle was found to be stored in associated adipocytes. When returned to clean seawater, WSF accumulated in the dorsal white muscle was released much faster than that in the adipocytes. These results indicated that the loose association of WSF with the nonlipid portion of white muscle, mainly muscle cells and intercellular fluid, is responsible for the rapid discharge of WSF from the dorsal muscle tissue in the early stages of depuration. After 4 d of depuration, the adipocytes became the principal storage site of residual WSF in white muscle and the depuration of WSF from muscle tissue then reflected the release of WSF from adipocytes in the muscle tissue. After 20 d of depuration, 10.7 ppm of tainting WSF in the form of high molecular weight aromatic hydrocarbons (mainly C₄-benzenes, naphthalene and alkylated naphthalenes) were still present in adipocytes, while in the dorsal white muscle only a trace of total WSF was detected. Increases in the number of aromatic rings and the alkylations on the rings enhanced the accumulation and retention of individual hydrocarbons in both adipocytes and white muscle. From these studies we conclude that it is the adipocytes in the muscle tissue which control the actual accumulation and release of hydrocarbons in the whole muscle tissue of Atlantic salmon.