High Ratio of Dietary Palmitic Acid to DHA + EPA Induces Glucose Metabolic Disorder Through Endocrine and Transcriptional Regulation in Large Yellow Croaker (Larimichthys crocea)

Background/Objectives: Replacing fish oil with vegetable oil is an important measure for aquaculture to relieve the pressure of fish oil, but it is also easy to cause the growth decline and metabolic disorder of farmed animals, mainly due to the change in dietary fatty acids. This study investigated the regulatory effects of dietary fatty acid composition on glucose metabolism in large yellow croaker (Larimichthys crocea) with an initial weight of 30.51 ± 0.16 g. Methods: Three isonitrogenous (~43% crude protein) and isolipid (~11% crude lipid) diets were formulated as follows: control (CON, DHA/EPA-rich oil as primary lipid), moderate palmitic acid (MPA, 50% of DHA+EPA-rich oil was replaced by glyceryl palmitate), and high palmitic acid (HPA, 100% of DHA+EPA-rich oil was replaced by glyceryl palmitate). Results: After 10 weeks of feeding, the HPA significantly reduced the liver/muscle glycogen contents, increased the liver lipid content, decreased the serum leptin/insulin level, and increased the adiponectin level. The levels of DHA and EPA in liver were decreased significantly. Transcriptionally, HPA upregulated hepatic glucokinase (gk, glycolysis) but down-regulated glycogen synthase (gys) and insulin/irs2 (insulin pathway) while inhibiting muscle ampk and leptin receptor (lepr). Conclusions: This study showed that high dietary PA/(DHA + EPA) impacted glycolipid homeostasis through endocrine and transcriptional regulation, leading to increased crude lipid and decreased glycogen levels, which provides a theoretical basis for scientific aquatic feed fatty acid formulation.