Besides growth performance, another exciting observation in the present study was that the whole-body and tissue lipid accumulation
in turbot was significantly modulated by the dietary inclusion of FPH.
This is the first study comprehensively evaluating the modulatory effects
of FPH on lipid accumulation in various fish tissues. The influence
of dietary FPH on lipid metabolism was first observed in murine
research. The FPH fed rats/mice had reduced TAG levels in liver and
plasma. In another fish
study on Atlantic salmon fed high plant-protein-based diets, as well as
in our previous studies on turbot and Japanese flounder, itwas observed
that certain levels of dietary FPH reduced the viscerosomatic index or
whole-body lipid content. These results are in agreement with the present study,
which showed reduced viscerosomatic index, gut lipid concentration, and
whole-body lipid concentration in treatments with high dietary FPH
levels. The TAG and cholesterol concentrations in serum were also
reduced by dietary FPH supplementations. This provided growing
evidence for the lipid-reducing effects of dietary FPH. Regarding the
involved mechanisms, the rodent studies suggested that dietary FPH
could reduce the fatty acid synthesis and induced the lipid oxidation
and energy expenditure .
In the present study, with respect to the lipid fraction affected in the
tissues stated above, dietary FPH reduced the neutral lipid concentrations
but did not affect the polar lipid concentrations. This may provide new
evidence for the speculation that dietary FPH reduces lipid accumulation
through inducing lipid oxidation and energy expenditure since neutral
lipids are primarily used as energy source. However, on the other hand,
the fatty acid analysis also showed that C16:0 was the predominantly
reduced fatty acid in gut. This indicates that FPH may also modulate the
fatty acid synthesis since C16:0 was the terminal product of denovo
lipogenesis.