Daily changes in parameters of energy metabolism in liver, white muscle, and gills of rainbow trout: Dependence on feeding

We assessed the daily patterns of parameters involved in energy metabolism in liver, white muscle, and gills of rainbow trout. Where daily rhythms were found, we analyzed the potential influence of feeding. Immature rainbow trout were randomly distributed in 3 groups: fish fed for 7 days, fish fasted for 7 days, and fish fasted for 7 days and refed for 4 days. On sampling day, fish of fed and refed groups were fed at 11.00 h, and all fish were sampled from each treatment group using the following time schedule: 14.00, 18.00, 21.00, 00.00, 04.00, 07.00, 10.00 and 14.00 h. The results obtained from metabolic parameters can be grouped into four different categories, such as i) those displaying no daily changes in any group assessed in liver (acetoacetate and lactate levels), white muscle (protein levels, and low Km (glucose) hexokinase (HK) and HK-IV activities) and gills (protein levels), ii) those displaying no 24 h changes in fed fish but in refed or fasted fish in liver (glucose, glycogen, amino acid and protein levels, and HK-IV activity), white muscle (glycogen and amino acid levels) and gills (glucose levels), iii) those displaying 24 h changes that were apparently dependent on feeding since they disappear in fasted fish in liver (Low Km (glucose) HK, lactate dehydrogenase (LDH-O), glucose 6-phosphatase (G6Pase), fructose 1,6-bisphosphatase (FBPase) , α-glycerophosphate dehydrogenase (G3PDH), glutamate dehydrogenase (GDH) and aspartate aminotransferase (Asp-AT) activities), white muscle (glucose levels, and pyruvate kinase (PK), LDH-O, G3PDH and Asp-AT activities) and gills (glycogen and lactate levels, and Low Km (glucose) HK, HK-IV, LDH-O and Asp-AT activities), and iv) those parameters displaying 24 h changes apparently not dependent on feeding in liver (lactate levels and PK activity) and gills (amino acid levels, and PK and GDH activities). In general, most 24 h changes observed were dependent on feeding and can be also related to daily changes in activity.