Potential capacity of Senegalese sole (Solea senegalensis) to use carbohydrates: Metabolic responses to hypo- and hyper-glycaemia

Glucose tolerance in fish is species-dependent and closely related to feeding habits. The capacity of each species to regulate glucose homeostasis is indicative of its potential to utilize dietary carbohydrates (CH). Senegalese sole is a carnivorous species but its nutrient requirements are still under debate. In the present study, we aimed to evaluate the capacity of Senegalese sole (20±4g) reared at 20°C to cope with marked changes in circulating levels of glucose through assessment of glucose tolerance by an oral glucose tolerance test and metabolic responses after induction of hyper-glycaemic and hypo-glycaemic conditions by intraperitoneal injections of D-glucose (600mgkg−X1 body mass) or insulin (5mgkg−1 body mass), respectively. Changes observed in the levels of metabolites and enzyme activities at hepatic level show a metabolic response to counter-regulate acute changes in circulating glucose levels. Thus, glycogen levels in liver decreased markedly in hypo-glycaemic fish (16-fold change) and increased in hyper-glycaemic fish (1.3-fold change) compared with normo-glycaemic fish 24h after treatment. Furthermore, activities of G6Pase (involved in gluconeogenesis) and GPase (involved in glycogenolysis) were higher in hypo- than in hyper-glycaemic fish after 24h of treatment (2.9-fold change for G6Pase and 7.1-fold change for GPase). The present results indicate that Senegalese sole has a fast plasma clearance rate of glucose compared with other carnivorous fish species and show a good capacity to deal with different glycaemic conditions by undertaking metabolic changes able to restore glucose homeostasis. These results suggest that Senegalese sole may be able to use dietary CH efficiently, allowing the incorporation of more sustainable and cheaper energy sources in aquafeeds for this species.