Effect of dietary carbohydrates on growth performance, feed efficiency and glucose metabolism in common snook (Centropomus undecimalis) and yellowtail snapper (Ocyurus chrysurus) juveniles

In recent years, interest in commercial farming of the common snook Centropomus undecimalis and yellowtail snapper Ocyurus chrysurus has been increasing in the Atlantic West; however, these species are carnivorous with a high protein requirement in the diet. A 75-day feeding trial was conducted to evaluate the effect of dietary carbohydrates on growth performance, feed efficiency, glycemic response, digestive and key liver enzymes of intermediary metabolism of C. undecimalis and O. chrysurus. Two diets were formulated to contain 51.6% protein, 7.9% lipid and 20% corn starch (High digestive carbohydrates diet, HC) or 20% wheat bran (Control diet, C). Growth performance was not affected by dietary carbohydrates in both species. The feed efficiency (FE) and protein efficiency ratio (PER) improved in C. undecimalis fed the HC diet; however, for O. chrysurus, FE and PER were not affected by the HC diet. The hepatic glycogen and whole-body lipid content increased in C. undecimalis fed the HC diet, but this did not occur in O. chrysurus. Intestinal amylase activity increased in both species with the HC diet. Blood glucose peaked in C. undecimalis six hours after being fed with the HC diet (7.8 mmol L−1), whereas the glucose peak in O. chrysurus occurred until nine hours (14.1 mmol L−1). Hepatic glucokinase (GK) activity increased with the HC diet in both fish species. However, at the molecular level, GK mRNA expression was higher in C. undecimalis fed the HC diet, but for O. chrysurus, GK mRNA expression did not differ between diets. Glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) activities increased only in C. undecimalis fed the HC diet. Pyruvate kinase (PK) increased and fructose-1, 6-bisphosphatase (FBPase) decreased in both species fed the HC diet. Alanine aminotransferase (ALT) activity was unaffected by experimental diets, but O. chrysurus showed higher activity than C. undecimalis. These results suggest that both fish species are able to adapt to a high-carbohydrate diet by reorganization carbohydrate metabolism. However, C. undecimalis showed a greater capacity to utilize and store carbohydrates than O. chrysurus.