Taking into consideration the data related to the total liver lipid and glycogen contents obtained in the present study, it could be assumed that the intermediary metabolism of carp is characterized by the use of lipids, mainly, for their energy requirements.
This hypothesis is supported by the lowest total liver lipid levels observed in black-adapted fish, which also showed the highest plasma total lipid levels and cortisol as well.
Catabolic action of cortisol on lipids metabolism reducing total liver content and promoting plasma free fatty acids (FFA) metabolism, has been observed in a number of both fresh and seawater teleost species (Pickering and Pottinger, 1995; Sheridan, 1986)