Metabolic responses to short starvation and refeeding in Dicentrarchus labrax. Effect of dietary composition

A study was conducted to assess the particular metabolic strategies of the European sea bass (Dicentrarchus labrax) to face a short starvation period and subsequent refeeding, and to evaluate the influence of the past nutritional history on such responses. With this purpose, two isoenergetic diets containing 42% and 50% of protein were formulated. Each diet was supplied to triplicate groups of European sea bass (I.W. 71.4 g.) for 22 days; then fish were starved for 9 days and later refed for 12 days with the same diet fed prior to starvation. Liver and blood were sampled at the end of the first feeding period (control point, 22F), at the first, third and ninth day of starvation (1S, 3S and 9S) and at the first, third and twelfth day of refeeding (1R, 3R and 12R). Growth performance, feed efficiency, plasma metabolite levels, liver composition, and hepatic activity of key enzymes of intermediary metabolism were evaluated. Prior to starvation, fish fed on diet 42P showed plasma triglyceride and total lipid levels and liver glycogen content higher and total amino acids lower than fish fed on diet 50P. Liver FBPase, GPT and GOT activities were also lower in 42P group. This may be due to a protein sparing effect and lower gluconeogenesis in that group, associated to the higher carbohydrate and lower protein intakes. Starvation induced a decrease in plasma metabolites and liver glycogen in both groups. After 9 days of starvation, plasma glucose in 42P group remained higher than in 50P group. During starvation, activities of FAS and HK significantly decreased in both groups. FPBase, G6PDH and GPT activities significantly decreased and GDH significantly increased only in group fed on diet 50P, whereas in 42P group the activity of these enzymes was not significantly different from the pre-starvation values. After 12 days of refeeding, most parameters evaluated returned to pre-starvation levels, except for 42P group in which values for enzymes involved in lipogenesis (FAS, G6PDH), glycaemia and cholesterolaemia were lower and GDH activity was higher than observed prior to starvation. In conclusion, results of this study showed that sea bass experience rapid metabolic adjustments to both short starvation and refeeding and that diet composition significantly influences the metabolic responses to these nutritional challenges.