Comparative lipid class analysis of fall and spring Pacific herring (Clupea pallasi)

Pacific herring (Clupea pallasi) must cope with challenges posed by the extreme seasonal environment of the North Pacific. These include dramatic seasonal variation in light, temperature, and plankton biomass. One of the most taxing challenges for herring is the lack of prey, primarily plankton, during winter. C. pallasi have adapted to survive this period of scarcity by building up energy reserves in the form of stored lipids during the productive summer months. Reduction of prey biomass in winter marks the beginning of a starvation period for C. pallasi during which catabolism of stored lipids replaces foraging as the primary source of energy. As a result of this shift in energy source, the herring undergo a general restructuring of metabolism wherein fatty acid, mainly derived from triacylglycerol, replaces glucose as the primary metabolite. In extreme starvation energy can also be derived from phospholipid and protein breakdown. To further explore bioenergetic survival strategies of herring, this study analyzed lipid concentrations in juvenile C. pallasi caught in Alaska’s Prince William Sound in the fall of 2009 and spring of 2010. Lipid content, body mass, and heart mass were compared between fall and spring herring. From fall to spring, body mass decreased 14% while total lipid content decreased 61%. Triacylglycerol, phospholipid, and cholesterol decreased by 74%, 64%, and 24%, respectively. The disproportionate decrease in specific lipids suggests that triacylglycerol, phospholipid, and cholesterol were catabolized or otherwise degraded during winter. In addition to loss of lipid, this study documented a 23% decrease in heart mass that suggests protein catabolism coincided with lipid catabolism. Remarkably, C. pallasi survive the winter despite these dramatic losses in lipid and protein. This suggests that precise metabolic allocation allows C. pallasi to minimize fitness consequences of starvation to survive in the challenging ecosystem of Prince William Sound.